| /* |
| * Read-Copy Update mechanism for mutual exclusion |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; either version 2 of the License, or |
| * (at your option) any later version. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| * GNU General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with this program; if not, you can access it online at |
| * http://www.gnu.org/licenses/gpl-2.0.html. |
| * |
| * Copyright IBM Corporation, 2008 |
| * |
| * Authors: Dipankar Sarma <dipankar@in.ibm.com> |
| * Manfred Spraul <manfred@colorfullife.com> |
| * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version |
| * |
| * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
| * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
| * |
| * For detailed explanation of Read-Copy Update mechanism see - |
| * Documentation/RCU |
| */ |
| #include <linux/types.h> |
| #include <linux/kernel.h> |
| #include <linux/init.h> |
| #include <linux/spinlock.h> |
| #include <linux/smp.h> |
| #include <linux/rcupdate_wait.h> |
| #include <linux/interrupt.h> |
| #include <linux/sched.h> |
| #include <linux/sched/debug.h> |
| #include <linux/nmi.h> |
| #include <linux/atomic.h> |
| #include <linux/bitops.h> |
| #include <linux/export.h> |
| #include <linux/completion.h> |
| #include <linux/moduleparam.h> |
| #include <linux/percpu.h> |
| #include <linux/notifier.h> |
| #include <linux/cpu.h> |
| #include <linux/mutex.h> |
| #include <linux/time.h> |
| #include <linux/kernel_stat.h> |
| #include <linux/wait.h> |
| #include <linux/kthread.h> |
| #include <uapi/linux/sched/types.h> |
| #include <linux/prefetch.h> |
| #include <linux/delay.h> |
| #include <linux/stop_machine.h> |
| #include <linux/random.h> |
| #include <linux/trace_events.h> |
| #include <linux/suspend.h> |
| #include <linux/ftrace.h> |
| |
| #include "tree.h" |
| #include "rcu.h" |
| |
| #ifdef MODULE_PARAM_PREFIX |
| #undef MODULE_PARAM_PREFIX |
| #endif |
| #define MODULE_PARAM_PREFIX "rcutree." |
| |
| /* Data structures. */ |
| |
| /* |
| * In order to export the rcu_state name to the tracing tools, it |
| * needs to be added in the __tracepoint_string section. |
| * This requires defining a separate variable tp_<sname>_varname |
| * that points to the string being used, and this will allow |
| * the tracing userspace tools to be able to decipher the string |
| * address to the matching string. |
| */ |
| #ifdef CONFIG_TRACING |
| # define DEFINE_RCU_TPS(sname) \ |
| static char sname##_varname[] = #sname; \ |
| static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; |
| # define RCU_STATE_NAME(sname) sname##_varname |
| #else |
| # define DEFINE_RCU_TPS(sname) |
| # define RCU_STATE_NAME(sname) __stringify(sname) |
| #endif |
| |
| #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \ |
| DEFINE_RCU_TPS(sname) \ |
| static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \ |
| struct rcu_state sname##_state = { \ |
| .level = { &sname##_state.node[0] }, \ |
| .rda = &sname##_data, \ |
| .call = cr, \ |
| .gp_state = RCU_GP_IDLE, \ |
| .gpnum = 0UL - 300UL, \ |
| .completed = 0UL - 300UL, \ |
| .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ |
| .name = RCU_STATE_NAME(sname), \ |
| .abbr = sabbr, \ |
| .exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \ |
| .exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \ |
| } |
| |
| RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched); |
| RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh); |
| |
| static struct rcu_state *const rcu_state_p; |
| LIST_HEAD(rcu_struct_flavors); |
| |
| /* Dump rcu_node combining tree at boot to verify correct setup. */ |
| static bool dump_tree; |
| module_param(dump_tree, bool, 0444); |
| /* Control rcu_node-tree auto-balancing at boot time. */ |
| static bool rcu_fanout_exact; |
| module_param(rcu_fanout_exact, bool, 0444); |
| /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */ |
| static int rcu_fanout_leaf = RCU_FANOUT_LEAF; |
| module_param(rcu_fanout_leaf, int, 0444); |
| int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; |
| /* Number of rcu_nodes at specified level. */ |
| int num_rcu_lvl[] = NUM_RCU_LVL_INIT; |
| int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ |
| /* panic() on RCU Stall sysctl. */ |
| int sysctl_panic_on_rcu_stall __read_mostly; |
| |
| /* |
| * The rcu_scheduler_active variable is initialized to the value |
| * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the |
| * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE, |
| * RCU can assume that there is but one task, allowing RCU to (for example) |
| * optimize synchronize_rcu() to a simple barrier(). When this variable |
| * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required |
| * to detect real grace periods. This variable is also used to suppress |
| * boot-time false positives from lockdep-RCU error checking. Finally, it |
| * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU |
| * is fully initialized, including all of its kthreads having been spawned. |
| */ |
| int rcu_scheduler_active __read_mostly; |
| EXPORT_SYMBOL_GPL(rcu_scheduler_active); |
| |
| /* |
| * The rcu_scheduler_fully_active variable transitions from zero to one |
| * during the early_initcall() processing, which is after the scheduler |
| * is capable of creating new tasks. So RCU processing (for example, |
| * creating tasks for RCU priority boosting) must be delayed until after |
| * rcu_scheduler_fully_active transitions from zero to one. We also |
| * currently delay invocation of any RCU callbacks until after this point. |
| * |
| * It might later prove better for people registering RCU callbacks during |
| * early boot to take responsibility for these callbacks, but one step at |
| * a time. |
| */ |
| static int rcu_scheduler_fully_active __read_mostly; |
| |
| static void rcu_init_new_rnp(struct rcu_node *rnp_leaf); |
| static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf); |
| static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); |
| static void invoke_rcu_core(void); |
| static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); |
| static void rcu_report_exp_rdp(struct rcu_state *rsp, |
| struct rcu_data *rdp, bool wake); |
| static void sync_sched_exp_online_cleanup(int cpu); |
| |
| /* rcuc/rcub kthread realtime priority */ |
| static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; |
| module_param(kthread_prio, int, 0644); |
| |
| /* Delay in jiffies for grace-period initialization delays, debug only. */ |
| |
| static int gp_preinit_delay; |
| module_param(gp_preinit_delay, int, 0444); |
| static int gp_init_delay; |
| module_param(gp_init_delay, int, 0444); |
| static int gp_cleanup_delay; |
| module_param(gp_cleanup_delay, int, 0444); |
| |
| /* |
| * Number of grace periods between delays, normalized by the duration of |
| * the delay. The longer the delay, the more the grace periods between |
| * each delay. The reason for this normalization is that it means that, |
| * for non-zero delays, the overall slowdown of grace periods is constant |
| * regardless of the duration of the delay. This arrangement balances |
| * the need for long delays to increase some race probabilities with the |
| * need for fast grace periods to increase other race probabilities. |
| */ |
| #define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */ |
| |
| /* |
| * Track the rcutorture test sequence number and the update version |
| * number within a given test. The rcutorture_testseq is incremented |
| * on every rcutorture module load and unload, so has an odd value |
| * when a test is running. The rcutorture_vernum is set to zero |
| * when rcutorture starts and is incremented on each rcutorture update. |
| * These variables enable correlating rcutorture output with the |
| * RCU tracing information. |
| */ |
| unsigned long rcutorture_testseq; |
| unsigned long rcutorture_vernum; |
| |
| /* |
| * Compute the mask of online CPUs for the specified rcu_node structure. |
| * This will not be stable unless the rcu_node structure's ->lock is |
| * held, but the bit corresponding to the current CPU will be stable |
| * in most contexts. |
| */ |
| unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp) |
| { |
| return READ_ONCE(rnp->qsmaskinitnext); |
| } |
| |
| /* |
| * Return true if an RCU grace period is in progress. The READ_ONCE()s |
| * permit this function to be invoked without holding the root rcu_node |
| * structure's ->lock, but of course results can be subject to change. |
| */ |
| static int rcu_gp_in_progress(struct rcu_state *rsp) |
| { |
| return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum); |
| } |
| |
| /* |
| * Note a quiescent state. Because we do not need to know |
| * how many quiescent states passed, just if there was at least |
| * one since the start of the grace period, this just sets a flag. |
| * The caller must have disabled preemption. |
| */ |
| void rcu_sched_qs(void) |
| { |
| RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!"); |
| if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s)) |
| return; |
| trace_rcu_grace_period(TPS("rcu_sched"), |
| __this_cpu_read(rcu_sched_data.gpnum), |
| TPS("cpuqs")); |
| __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false); |
| if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) |
| return; |
| __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false); |
| rcu_report_exp_rdp(&rcu_sched_state, |
| this_cpu_ptr(&rcu_sched_data), true); |
| } |
| |
| void rcu_bh_qs(void) |
| { |
| RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!"); |
| if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) { |
| trace_rcu_grace_period(TPS("rcu_bh"), |
| __this_cpu_read(rcu_bh_data.gpnum), |
| TPS("cpuqs")); |
| __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false); |
| } |
| } |
| |
| /* |
| * Steal a bit from the bottom of ->dynticks for idle entry/exit |
| * control. Initially this is for TLB flushing. |
| */ |
| #define RCU_DYNTICK_CTRL_MASK 0x1 |
| #define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1) |
| #ifndef rcu_eqs_special_exit |
| #define rcu_eqs_special_exit() do { } while (0) |
| #endif |
| |
| static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { |
| .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE, |
| .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR), |
| }; |
| |
| /* |
| * There's a few places, currently just in the tracing infrastructure, |
| * that uses rcu_irq_enter() to make sure RCU is watching. But there's |
| * a small location where that will not even work. In those cases |
| * rcu_irq_enter_disabled() needs to be checked to make sure rcu_irq_enter() |
| * can be called. |
| */ |
| static DEFINE_PER_CPU(bool, disable_rcu_irq_enter); |
| |
| bool rcu_irq_enter_disabled(void) |
| { |
| return this_cpu_read(disable_rcu_irq_enter); |
| } |
| |
| /* |
| * Record entry into an extended quiescent state. This is only to be |
| * called when not already in an extended quiescent state. |
| */ |
| static void rcu_dynticks_eqs_enter(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| int seq; |
| |
| /* |
| * CPUs seeing atomic_add_return() must see prior RCU read-side |
| * critical sections, and we also must force ordering with the |
| * next idle sojourn. |
| */ |
| seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks); |
| /* Better be in an extended quiescent state! */ |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| (seq & RCU_DYNTICK_CTRL_CTR)); |
| /* Better not have special action (TLB flush) pending! */ |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| (seq & RCU_DYNTICK_CTRL_MASK)); |
| } |
| |
| /* |
| * Record exit from an extended quiescent state. This is only to be |
| * called from an extended quiescent state. |
| */ |
| static void rcu_dynticks_eqs_exit(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| int seq; |
| |
| /* |
| * CPUs seeing atomic_add_return() must see prior idle sojourns, |
| * and we also must force ordering with the next RCU read-side |
| * critical section. |
| */ |
| seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks); |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| !(seq & RCU_DYNTICK_CTRL_CTR)); |
| if (seq & RCU_DYNTICK_CTRL_MASK) { |
| atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks); |
| smp_mb__after_atomic(); /* _exit after clearing mask. */ |
| /* Prefer duplicate flushes to losing a flush. */ |
| rcu_eqs_special_exit(); |
| } |
| } |
| |
| /* |
| * Reset the current CPU's ->dynticks counter to indicate that the |
| * newly onlined CPU is no longer in an extended quiescent state. |
| * This will either leave the counter unchanged, or increment it |
| * to the next non-quiescent value. |
| * |
| * The non-atomic test/increment sequence works because the upper bits |
| * of the ->dynticks counter are manipulated only by the corresponding CPU, |
| * or when the corresponding CPU is offline. |
| */ |
| static void rcu_dynticks_eqs_online(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| |
| if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR) |
| return; |
| atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks); |
| } |
| |
| /* |
| * Is the current CPU in an extended quiescent state? |
| * |
| * No ordering, as we are sampling CPU-local information. |
| */ |
| bool rcu_dynticks_curr_cpu_in_eqs(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| |
| return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR); |
| } |
| |
| /* |
| * Snapshot the ->dynticks counter with full ordering so as to allow |
| * stable comparison of this counter with past and future snapshots. |
| */ |
| int rcu_dynticks_snap(struct rcu_dynticks *rdtp) |
| { |
| int snap = atomic_add_return(0, &rdtp->dynticks); |
| |
| return snap & ~RCU_DYNTICK_CTRL_MASK; |
| } |
| |
| /* |
| * Return true if the snapshot returned from rcu_dynticks_snap() |
| * indicates that RCU is in an extended quiescent state. |
| */ |
| static bool rcu_dynticks_in_eqs(int snap) |
| { |
| return !(snap & RCU_DYNTICK_CTRL_CTR); |
| } |
| |
| /* |
| * Return true if the CPU corresponding to the specified rcu_dynticks |
| * structure has spent some time in an extended quiescent state since |
| * rcu_dynticks_snap() returned the specified snapshot. |
| */ |
| static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap) |
| { |
| return snap != rcu_dynticks_snap(rdtp); |
| } |
| |
| /* |
| * Do a double-increment of the ->dynticks counter to emulate a |
| * momentary idle-CPU quiescent state. |
| */ |
| static void rcu_dynticks_momentary_idle(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR, |
| &rdtp->dynticks); |
| |
| /* It is illegal to call this from idle state. */ |
| WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR)); |
| } |
| |
| /* |
| * Set the special (bottom) bit of the specified CPU so that it |
| * will take special action (such as flushing its TLB) on the |
| * next exit from an extended quiescent state. Returns true if |
| * the bit was successfully set, or false if the CPU was not in |
| * an extended quiescent state. |
| */ |
| bool rcu_eqs_special_set(int cpu) |
| { |
| int old; |
| int new; |
| struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
| |
| do { |
| old = atomic_read(&rdtp->dynticks); |
| if (old & RCU_DYNTICK_CTRL_CTR) |
| return false; |
| new = old | RCU_DYNTICK_CTRL_MASK; |
| } while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old); |
| return true; |
| } |
| |
| /* |
| * Let the RCU core know that this CPU has gone through the scheduler, |
| * which is a quiescent state. This is called when the need for a |
| * quiescent state is urgent, so we burn an atomic operation and full |
| * memory barriers to let the RCU core know about it, regardless of what |
| * this CPU might (or might not) do in the near future. |
| * |
| * We inform the RCU core by emulating a zero-duration dyntick-idle period. |
| * |
| * The caller must have disabled interrupts. |
| */ |
| static void rcu_momentary_dyntick_idle(void) |
| { |
| raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false); |
| rcu_dynticks_momentary_idle(); |
| } |
| |
| /* |
| * Note a context switch. This is a quiescent state for RCU-sched, |
| * and requires special handling for preemptible RCU. |
| * The caller must have disabled interrupts. |
| */ |
| void rcu_note_context_switch(bool preempt) |
| { |
| barrier(); /* Avoid RCU read-side critical sections leaking down. */ |
| trace_rcu_utilization(TPS("Start context switch")); |
| rcu_sched_qs(); |
| rcu_preempt_note_context_switch(preempt); |
| /* Load rcu_urgent_qs before other flags. */ |
| if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) |
| goto out; |
| this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); |
| if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) |
| rcu_momentary_dyntick_idle(); |
| this_cpu_inc(rcu_dynticks.rcu_qs_ctr); |
| if (!preempt) |
| rcu_note_voluntary_context_switch_lite(current); |
| out: |
| trace_rcu_utilization(TPS("End context switch")); |
| barrier(); /* Avoid RCU read-side critical sections leaking up. */ |
| } |
| EXPORT_SYMBOL_GPL(rcu_note_context_switch); |
| |
| /* |
| * Register a quiescent state for all RCU flavors. If there is an |
| * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight |
| * dyntick-idle quiescent state visible to other CPUs (but only for those |
| * RCU flavors in desperate need of a quiescent state, which will normally |
| * be none of them). Either way, do a lightweight quiescent state for |
| * all RCU flavors. |
| * |
| * The barrier() calls are redundant in the common case when this is |
| * called externally, but just in case this is called from within this |
| * file. |
| * |
| */ |
| void rcu_all_qs(void) |
| { |
| unsigned long flags; |
| |
| if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs)) |
| return; |
| preempt_disable(); |
| /* Load rcu_urgent_qs before other flags. */ |
| if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) { |
| preempt_enable(); |
| return; |
| } |
| this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); |
| barrier(); /* Avoid RCU read-side critical sections leaking down. */ |
| if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) { |
| local_irq_save(flags); |
| rcu_momentary_dyntick_idle(); |
| local_irq_restore(flags); |
| } |
| if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))) |
| rcu_sched_qs(); |
| this_cpu_inc(rcu_dynticks.rcu_qs_ctr); |
| barrier(); /* Avoid RCU read-side critical sections leaking up. */ |
| preempt_enable(); |
| } |
| EXPORT_SYMBOL_GPL(rcu_all_qs); |
| |
| #define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch. */ |
| static long blimit = DEFAULT_RCU_BLIMIT; |
| #define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */ |
| static long qhimark = DEFAULT_RCU_QHIMARK; |
| #define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */ |
| static long qlowmark = DEFAULT_RCU_QLOMARK; |
| |
| module_param(blimit, long, 0444); |
| module_param(qhimark, long, 0444); |
| module_param(qlowmark, long, 0444); |
| |
| static ulong jiffies_till_first_fqs = ULONG_MAX; |
| static ulong jiffies_till_next_fqs = ULONG_MAX; |
| static bool rcu_kick_kthreads; |
| |
| module_param(jiffies_till_first_fqs, ulong, 0644); |
| module_param(jiffies_till_next_fqs, ulong, 0644); |
| module_param(rcu_kick_kthreads, bool, 0644); |
| |
| /* |
| * How long the grace period must be before we start recruiting |
| * quiescent-state help from rcu_note_context_switch(). |
| */ |
| static ulong jiffies_till_sched_qs = HZ / 20; |
| module_param(jiffies_till_sched_qs, ulong, 0644); |
| |
| static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, |
| struct rcu_data *rdp); |
| static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp)); |
| static void force_quiescent_state(struct rcu_state *rsp); |
| static int rcu_pending(void); |
| |
| /* |
| * Return the number of RCU batches started thus far for debug & stats. |
| */ |
| unsigned long rcu_batches_started(void) |
| { |
| return rcu_state_p->gpnum; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_started); |
| |
| /* |
| * Return the number of RCU-sched batches started thus far for debug & stats. |
| */ |
| unsigned long rcu_batches_started_sched(void) |
| { |
| return rcu_sched_state.gpnum; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_started_sched); |
| |
| /* |
| * Return the number of RCU BH batches started thus far for debug & stats. |
| */ |
| unsigned long rcu_batches_started_bh(void) |
| { |
| return rcu_bh_state.gpnum; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_started_bh); |
| |
| /* |
| * Return the number of RCU batches completed thus far for debug & stats. |
| */ |
| unsigned long rcu_batches_completed(void) |
| { |
| return rcu_state_p->completed; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_completed); |
| |
| /* |
| * Return the number of RCU-sched batches completed thus far for debug & stats. |
| */ |
| unsigned long rcu_batches_completed_sched(void) |
| { |
| return rcu_sched_state.completed; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_completed_sched); |
| |
| /* |
| * Return the number of RCU BH batches completed thus far for debug & stats. |
| */ |
| unsigned long rcu_batches_completed_bh(void) |
| { |
| return rcu_bh_state.completed; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); |
| |
| /* |
| * Return the number of RCU expedited batches completed thus far for |
| * debug & stats. Odd numbers mean that a batch is in progress, even |
| * numbers mean idle. The value returned will thus be roughly double |
| * the cumulative batches since boot. |
| */ |
| unsigned long rcu_exp_batches_completed(void) |
| { |
| return rcu_state_p->expedited_sequence; |
| } |
| EXPORT_SYMBOL_GPL(rcu_exp_batches_completed); |
| |
| /* |
| * Return the number of RCU-sched expedited batches completed thus far |
| * for debug & stats. Similar to rcu_exp_batches_completed(). |
| */ |
| unsigned long rcu_exp_batches_completed_sched(void) |
| { |
| return rcu_sched_state.expedited_sequence; |
| } |
| EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched); |
| |
| /* |
| * Force a quiescent state. |
| */ |
| void rcu_force_quiescent_state(void) |
| { |
| force_quiescent_state(rcu_state_p); |
| } |
| EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
| |
| /* |
| * Force a quiescent state for RCU BH. |
| */ |
| void rcu_bh_force_quiescent_state(void) |
| { |
| force_quiescent_state(&rcu_bh_state); |
| } |
| EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); |
| |
| /* |
| * Force a quiescent state for RCU-sched. |
| */ |
| void rcu_sched_force_quiescent_state(void) |
| { |
| force_quiescent_state(&rcu_sched_state); |
| } |
| EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); |
| |
| /* |
| * Show the state of the grace-period kthreads. |
| */ |
| void show_rcu_gp_kthreads(void) |
| { |
| struct rcu_state *rsp; |
| |
| for_each_rcu_flavor(rsp) { |
| pr_info("%s: wait state: %d ->state: %#lx\n", |
| rsp->name, rsp->gp_state, rsp->gp_kthread->state); |
| /* sched_show_task(rsp->gp_kthread); */ |
| } |
| } |
| EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); |
| |
| /* |
| * Record the number of times rcutorture tests have been initiated and |
| * terminated. This information allows the debugfs tracing stats to be |
| * correlated to the rcutorture messages, even when the rcutorture module |
| * is being repeatedly loaded and unloaded. In other words, we cannot |
| * store this state in rcutorture itself. |
| */ |
| void rcutorture_record_test_transition(void) |
| { |
| rcutorture_testseq++; |
| rcutorture_vernum = 0; |
| } |
| EXPORT_SYMBOL_GPL(rcutorture_record_test_transition); |
| |
| /* |
| * Send along grace-period-related data for rcutorture diagnostics. |
| */ |
| void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, |
| unsigned long *gpnum, unsigned long *completed) |
| { |
| struct rcu_state *rsp = NULL; |
| |
| switch (test_type) { |
| case RCU_FLAVOR: |
| rsp = rcu_state_p; |
| break; |
| case RCU_BH_FLAVOR: |
| rsp = &rcu_bh_state; |
| break; |
| case RCU_SCHED_FLAVOR: |
| rsp = &rcu_sched_state; |
| break; |
| default: |
| break; |
| } |
| if (rsp == NULL) |
| return; |
| *flags = READ_ONCE(rsp->gp_flags); |
| *gpnum = READ_ONCE(rsp->gpnum); |
| *completed = READ_ONCE(rsp->completed); |
| } |
| EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); |
| |
| /* |
| * Record the number of writer passes through the current rcutorture test. |
| * This is also used to correlate debugfs tracing stats with the rcutorture |
| * messages. |
| */ |
| void rcutorture_record_progress(unsigned long vernum) |
| { |
| rcutorture_vernum++; |
| } |
| EXPORT_SYMBOL_GPL(rcutorture_record_progress); |
| |
| /* |
| * Return the root node of the specified rcu_state structure. |
| */ |
| static struct rcu_node *rcu_get_root(struct rcu_state *rsp) |
| { |
| return &rsp->node[0]; |
| } |
| |
| /* |
| * Is there any need for future grace periods? |
| * Interrupts must be disabled. If the caller does not hold the root |
| * rnp_node structure's ->lock, the results are advisory only. |
| */ |
| static int rcu_future_needs_gp(struct rcu_state *rsp) |
| { |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| int idx = (READ_ONCE(rnp->completed) + 1) & 0x1; |
| int *fp = &rnp->need_future_gp[idx]; |
| |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_future_needs_gp() invoked with irqs enabled!!!"); |
| return READ_ONCE(*fp); |
| } |
| |
| /* |
| * Does the current CPU require a not-yet-started grace period? |
| * The caller must have disabled interrupts to prevent races with |
| * normal callback registry. |
| */ |
| static bool |
| cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "cpu_needs_another_gp() invoked with irqs enabled!!!"); |
| if (rcu_gp_in_progress(rsp)) |
| return false; /* No, a grace period is already in progress. */ |
| if (rcu_future_needs_gp(rsp)) |
| return true; /* Yes, a no-CBs CPU needs one. */ |
| if (!rcu_segcblist_is_enabled(&rdp->cblist)) |
| return false; /* No, this is a no-CBs (or offline) CPU. */ |
| if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) |
| return true; /* Yes, CPU has newly registered callbacks. */ |
| if (rcu_segcblist_future_gp_needed(&rdp->cblist, |
| READ_ONCE(rsp->completed))) |
| return true; /* Yes, CBs for future grace period. */ |
| return false; /* No grace period needed. */ |
| } |
| |
| /* |
| * rcu_eqs_enter_common - current CPU is entering an extended quiescent state |
| * |
| * Enter idle, doing appropriate accounting. The caller must have |
| * disabled interrupts. |
| */ |
| static void rcu_eqs_enter_common(bool user) |
| { |
| struct rcu_state *rsp; |
| struct rcu_data *rdp; |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_eqs_enter_common() invoked with irqs enabled!!!"); |
| trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0); |
| if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| !user && !is_idle_task(current)) { |
| struct task_struct *idle __maybe_unused = |
| idle_task(smp_processor_id()); |
| |
| trace_rcu_dyntick(TPS("Error on entry: not idle task"), rdtp->dynticks_nesting, 0); |
| rcu_ftrace_dump(DUMP_ORIG); |
| WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", |
| current->pid, current->comm, |
| idle->pid, idle->comm); /* must be idle task! */ |
| } |
| for_each_rcu_flavor(rsp) { |
| rdp = this_cpu_ptr(rsp->rda); |
| do_nocb_deferred_wakeup(rdp); |
| } |
| rcu_prepare_for_idle(); |
| __this_cpu_inc(disable_rcu_irq_enter); |
| rdtp->dynticks_nesting = 0; /* Breaks tracing momentarily. */ |
| rcu_dynticks_eqs_enter(); /* After this, tracing works again. */ |
| __this_cpu_dec(disable_rcu_irq_enter); |
| rcu_dynticks_task_enter(); |
| |
| /* |
| * It is illegal to enter an extended quiescent state while |
| * in an RCU read-side critical section. |
| */ |
| RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), |
| "Illegal idle entry in RCU read-side critical section."); |
| RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), |
| "Illegal idle entry in RCU-bh read-side critical section."); |
| RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), |
| "Illegal idle entry in RCU-sched read-side critical section."); |
| } |
| |
| /* |
| * Enter an RCU extended quiescent state, which can be either the |
| * idle loop or adaptive-tickless usermode execution. |
| */ |
| static void rcu_eqs_enter(bool user) |
| { |
| struct rcu_dynticks *rdtp; |
| |
| rdtp = this_cpu_ptr(&rcu_dynticks); |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| (rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); |
| if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) |
| rcu_eqs_enter_common(user); |
| else |
| rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; |
| } |
| |
| /** |
| * rcu_idle_enter - inform RCU that current CPU is entering idle |
| * |
| * Enter idle mode, in other words, -leave- the mode in which RCU |
| * read-side critical sections can occur. (Though RCU read-side |
| * critical sections can occur in irq handlers in idle, a possibility |
| * handled by irq_enter() and irq_exit().) |
| * |
| * We crowbar the ->dynticks_nesting field to zero to allow for |
| * the possibility of usermode upcalls having messed up our count |
| * of interrupt nesting level during the prior busy period. |
| */ |
| void rcu_idle_enter(void) |
| { |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_idle_enter() invoked with irqs enabled!!!"); |
| rcu_eqs_enter(false); |
| } |
| |
| #ifdef CONFIG_NO_HZ_FULL |
| /** |
| * rcu_user_enter - inform RCU that we are resuming userspace. |
| * |
| * Enter RCU idle mode right before resuming userspace. No use of RCU |
| * is permitted between this call and rcu_user_exit(). This way the |
| * CPU doesn't need to maintain the tick for RCU maintenance purposes |
| * when the CPU runs in userspace. |
| */ |
| void rcu_user_enter(void) |
| { |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_user_enter() invoked with irqs enabled!!!"); |
| rcu_eqs_enter(true); |
| } |
| #endif /* CONFIG_NO_HZ_FULL */ |
| |
| /** |
| * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle |
| * |
| * Exit from an interrupt handler, which might possibly result in entering |
| * idle mode, in other words, leaving the mode in which read-side critical |
| * sections can occur. The caller must have disabled interrupts. |
| * |
| * This code assumes that the idle loop never does anything that might |
| * result in unbalanced calls to irq_enter() and irq_exit(). If your |
| * architecture violates this assumption, RCU will give you what you |
| * deserve, good and hard. But very infrequently and irreproducibly. |
| * |
| * Use things like work queues to work around this limitation. |
| * |
| * You have been warned. |
| */ |
| void rcu_irq_exit(void) |
| { |
| struct rcu_dynticks *rdtp; |
| |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!"); |
| rdtp = this_cpu_ptr(&rcu_dynticks); |
| |
| /* Page faults can happen in NMI handlers, so check... */ |
| if (rdtp->dynticks_nmi_nesting) |
| return; |
| |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| rdtp->dynticks_nesting < 1); |
| if (rdtp->dynticks_nesting <= 1) { |
| rcu_eqs_enter_common(true); |
| } else { |
| trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nesting, rdtp->dynticks_nesting - 1); |
| rdtp->dynticks_nesting--; |
| } |
| } |
| |
| /* |
| * Wrapper for rcu_irq_exit() where interrupts are enabled. |
| */ |
| void rcu_irq_exit_irqson(void) |
| { |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| rcu_irq_exit(); |
| local_irq_restore(flags); |
| } |
| |
| /* |
| * rcu_eqs_exit_common - current CPU moving away from extended quiescent state |
| * |
| * If the new value of the ->dynticks_nesting counter was previously zero, |
| * we really have exited idle, and must do the appropriate accounting. |
| * The caller must have disabled interrupts. |
| */ |
| static void rcu_eqs_exit_common(long long oldval, int user) |
| { |
| RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);) |
| |
| rcu_dynticks_task_exit(); |
| rcu_dynticks_eqs_exit(); |
| rcu_cleanup_after_idle(); |
| trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting); |
| if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| !user && !is_idle_task(current)) { |
| struct task_struct *idle __maybe_unused = |
| idle_task(smp_processor_id()); |
| |
| trace_rcu_dyntick(TPS("Error on exit: not idle task"), |
| oldval, rdtp->dynticks_nesting); |
| rcu_ftrace_dump(DUMP_ORIG); |
| WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", |
| current->pid, current->comm, |
| idle->pid, idle->comm); /* must be idle task! */ |
| } |
| } |
| |
| /* |
| * Exit an RCU extended quiescent state, which can be either the |
| * idle loop or adaptive-tickless usermode execution. |
| */ |
| static void rcu_eqs_exit(bool user) |
| { |
| struct rcu_dynticks *rdtp; |
| long long oldval; |
| |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_eqs_exit() invoked with irqs enabled!!!"); |
| rdtp = this_cpu_ptr(&rcu_dynticks); |
| oldval = rdtp->dynticks_nesting; |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); |
| if (oldval & DYNTICK_TASK_NEST_MASK) { |
| rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; |
| } else { |
| __this_cpu_inc(disable_rcu_irq_enter); |
| rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; |
| rcu_eqs_exit_common(oldval, user); |
| __this_cpu_dec(disable_rcu_irq_enter); |
| } |
| } |
| |
| /** |
| * rcu_idle_exit - inform RCU that current CPU is leaving idle |
| * |
| * Exit idle mode, in other words, -enter- the mode in which RCU |
| * read-side critical sections can occur. |
| * |
| * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to |
| * allow for the possibility of usermode upcalls messing up our count |
| * of interrupt nesting level during the busy period that is just |
| * now starting. |
| */ |
| void rcu_idle_exit(void) |
| { |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| rcu_eqs_exit(false); |
| local_irq_restore(flags); |
| } |
| |
| #ifdef CONFIG_NO_HZ_FULL |
| /** |
| * rcu_user_exit - inform RCU that we are exiting userspace. |
| * |
| * Exit RCU idle mode while entering the kernel because it can |
| * run a RCU read side critical section anytime. |
| */ |
| void rcu_user_exit(void) |
| { |
| rcu_eqs_exit(1); |
| } |
| #endif /* CONFIG_NO_HZ_FULL */ |
| |
| /** |
| * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle |
| * |
| * Enter an interrupt handler, which might possibly result in exiting |
| * idle mode, in other words, entering the mode in which read-side critical |
| * sections can occur. The caller must have disabled interrupts. |
| * |
| * Note that the Linux kernel is fully capable of entering an interrupt |
| * handler that it never exits, for example when doing upcalls to |
| * user mode! This code assumes that the idle loop never does upcalls to |
| * user mode. If your architecture does do upcalls from the idle loop (or |
| * does anything else that results in unbalanced calls to the irq_enter() |
| * and irq_exit() functions), RCU will give you what you deserve, good |
| * and hard. But very infrequently and irreproducibly. |
| * |
| * Use things like work queues to work around this limitation. |
| * |
| * You have been warned. |
| */ |
| void rcu_irq_enter(void) |
| { |
| struct rcu_dynticks *rdtp; |
| long long oldval; |
| |
| RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!"); |
| rdtp = this_cpu_ptr(&rcu_dynticks); |
| |
| /* Page faults can happen in NMI handlers, so check... */ |
| if (rdtp->dynticks_nmi_nesting) |
| return; |
| |
| oldval = rdtp->dynticks_nesting; |
| rdtp->dynticks_nesting++; |
| WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |
| rdtp->dynticks_nesting == 0); |
| if (oldval) |
| trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting); |
| else |
| rcu_eqs_exit_common(oldval, true); |
| } |
| |
| /* |
| * Wrapper for rcu_irq_enter() where interrupts are enabled. |
| */ |
| void rcu_irq_enter_irqson(void) |
| { |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| rcu_irq_enter(); |
| local_irq_restore(flags); |
| } |
| |
| /** |
| * rcu_nmi_enter - inform RCU of entry to NMI context |
| * |
| * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and |
| * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know |
| * that the CPU is active. This implementation permits nested NMIs, as |
| * long as the nesting level does not overflow an int. (You will probably |
| * run out of stack space first.) |
| */ |
| void rcu_nmi_enter(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| int incby = 2; |
| |
| /* Complain about underflow. */ |
| WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0); |
| |
| /* |
| * If idle from RCU viewpoint, atomically increment ->dynticks |
| * to mark non-idle and increment ->dynticks_nmi_nesting by one. |
| * Otherwise, increment ->dynticks_nmi_nesting by two. This means |
| * if ->dynticks_nmi_nesting is equal to one, we are guaranteed |
| * to be in the outermost NMI handler that interrupted an RCU-idle |
| * period (observation due to Andy Lutomirski). |
| */ |
| if (rcu_dynticks_curr_cpu_in_eqs()) { |
| rcu_dynticks_eqs_exit(); |
| incby = 1; |
| } |
| rdtp->dynticks_nmi_nesting += incby; |
| barrier(); |
| } |
| |
| /** |
| * rcu_nmi_exit - inform RCU of exit from NMI context |
| * |
| * If we are returning from the outermost NMI handler that interrupted an |
| * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting |
| * to let the RCU grace-period handling know that the CPU is back to |
| * being RCU-idle. |
| */ |
| void rcu_nmi_exit(void) |
| { |
| struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
| |
| /* |
| * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. |
| * (We are exiting an NMI handler, so RCU better be paying attention |
| * to us!) |
| */ |
| WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0); |
| WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs()); |
| |
| /* |
| * If the nesting level is not 1, the CPU wasn't RCU-idle, so |
| * leave it in non-RCU-idle state. |
| */ |
| if (rdtp->dynticks_nmi_nesting != 1) { |
| rdtp->dynticks_nmi_nesting -= 2; |
| return; |
| } |
| |
| /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ |
| rdtp->dynticks_nmi_nesting = 0; |
| rcu_dynticks_eqs_enter(); |
| } |
| |
| /** |
| * rcu_is_watching - see if RCU thinks that the current CPU is idle |
| * |
| * Return true if RCU is watching the running CPU, which means that this |
| * CPU can safely enter RCU read-side critical sections. In other words, |
| * if the current CPU is in its idle loop and is neither in an interrupt |
| * or NMI handler, return true. |
| */ |
| bool notrace rcu_is_watching(void) |
| { |
| bool ret; |
| |
| preempt_disable_notrace(); |
| ret = !rcu_dynticks_curr_cpu_in_eqs(); |
| preempt_enable_notrace(); |
| return ret; |
| } |
| EXPORT_SYMBOL_GPL(rcu_is_watching); |
| |
| /* |
| * If a holdout task is actually running, request an urgent quiescent |
| * state from its CPU. This is unsynchronized, so migrations can cause |
| * the request to go to the wrong CPU. Which is OK, all that will happen |
| * is that the CPU's next context switch will be a bit slower and next |
| * time around this task will generate another request. |
| */ |
| void rcu_request_urgent_qs_task(struct task_struct *t) |
| { |
| int cpu; |
| |
| barrier(); |
| cpu = task_cpu(t); |
| if (!task_curr(t)) |
| return; /* This task is not running on that CPU. */ |
| smp_store_release(per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, cpu), true); |
| } |
| |
| #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) |
| |
| /* |
| * Is the current CPU online? Disable preemption to avoid false positives |
| * that could otherwise happen due to the current CPU number being sampled, |
| * this task being preempted, its old CPU being taken offline, resuming |
| * on some other CPU, then determining that its old CPU is now offline. |
| * It is OK to use RCU on an offline processor during initial boot, hence |
| * the check for rcu_scheduler_fully_active. Note also that it is OK |
| * for a CPU coming online to use RCU for one jiffy prior to marking itself |
| * online in the cpu_online_mask. Similarly, it is OK for a CPU going |
| * offline to continue to use RCU for one jiffy after marking itself |
| * offline in the cpu_online_mask. This leniency is necessary given the |
| * non-atomic nature of the online and offline processing, for example, |
| * the fact that a CPU enters the scheduler after completing the teardown |
| * of the CPU. |
| * |
| * This is also why RCU internally marks CPUs online during in the |
| * preparation phase and offline after the CPU has been taken down. |
| * |
| * Disable checking if in an NMI handler because we cannot safely report |
| * errors from NMI handlers anyway. |
| */ |
| bool rcu_lockdep_current_cpu_online(void) |
| { |
| struct rcu_data *rdp; |
| struct rcu_node *rnp; |
| bool ret; |
| |
| if (in_nmi()) |
| return true; |
| preempt_disable(); |
| rdp = this_cpu_ptr(&rcu_sched_data); |
| rnp = rdp->mynode; |
| ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) || |
| !rcu_scheduler_fully_active; |
| preempt_enable(); |
| return ret; |
| } |
| EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); |
| |
| #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ |
| |
| /** |
| * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle |
| * |
| * If the current CPU is idle or running at a first-level (not nested) |
| * interrupt from idle, return true. The caller must have at least |
| * disabled preemption. |
| */ |
| static int rcu_is_cpu_rrupt_from_idle(void) |
| { |
| return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1; |
| } |
| |
| /* |
| * Snapshot the specified CPU's dynticks counter so that we can later |
| * credit them with an implicit quiescent state. Return 1 if this CPU |
| * is in dynticks idle mode, which is an extended quiescent state. |
| */ |
| static int dyntick_save_progress_counter(struct rcu_data *rdp) |
| { |
| rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks); |
| if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) { |
| trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); |
| if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4, |
| rdp->mynode->gpnum)) |
| WRITE_ONCE(rdp->gpwrap, true); |
| return 1; |
| } |
| return 0; |
| } |
| |
| /* |
| * Return true if the specified CPU has passed through a quiescent |
| * state by virtue of being in or having passed through an dynticks |
| * idle state since the last call to dyntick_save_progress_counter() |
| * for this same CPU, or by virtue of having been offline. |
| */ |
| static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) |
| { |
| unsigned long jtsq; |
| bool *rnhqp; |
| bool *ruqp; |
| unsigned long rjtsc; |
| struct rcu_node *rnp; |
| |
| /* |
| * If the CPU passed through or entered a dynticks idle phase with |
| * no active irq/NMI handlers, then we can safely pretend that the CPU |
| * already acknowledged the request to pass through a quiescent |
| * state. Either way, that CPU cannot possibly be in an RCU |
| * read-side critical section that started before the beginning |
| * of the current RCU grace period. |
| */ |
| if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) { |
| trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); |
| rdp->dynticks_fqs++; |
| return 1; |
| } |
| |
| /* Compute and saturate jiffies_till_sched_qs. */ |
| jtsq = jiffies_till_sched_qs; |
| rjtsc = rcu_jiffies_till_stall_check(); |
| if (jtsq > rjtsc / 2) { |
| WRITE_ONCE(jiffies_till_sched_qs, rjtsc); |
| jtsq = rjtsc / 2; |
| } else if (jtsq < 1) { |
| WRITE_ONCE(jiffies_till_sched_qs, 1); |
| jtsq = 1; |
| } |
| |
| /* |
| * Has this CPU encountered a cond_resched_rcu_qs() since the |
| * beginning of the grace period? For this to be the case, |
| * the CPU has to have noticed the current grace period. This |
| * might not be the case for nohz_full CPUs looping in the kernel. |
| */ |
| rnp = rdp->mynode; |
| ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu); |
| if (time_after(jiffies, rdp->rsp->gp_start + jtsq) && |
| READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) && |
| READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) { |
| trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc")); |
| return 1; |
| } else { |
| /* Load rcu_qs_ctr before store to rcu_urgent_qs. */ |
| smp_store_release(ruqp, true); |
| } |
| |
| /* Check for the CPU being offline. */ |
| if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) { |
| trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl")); |
| rdp->offline_fqs++; |
| return 1; |
| } |
| |
| /* |
| * A CPU running for an extended time within the kernel can |
| * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode, |
| * even context-switching back and forth between a pair of |
| * in-kernel CPU-bound tasks cannot advance grace periods. |
| * So if the grace period is old enough, make the CPU pay attention. |
| * Note that the unsynchronized assignments to the per-CPU |
| * rcu_need_heavy_qs variable are safe. Yes, setting of |
| * bits can be lost, but they will be set again on the next |
| * force-quiescent-state pass. So lost bit sets do not result |
| * in incorrect behavior, merely in a grace period lasting |
| * a few jiffies longer than it might otherwise. Because |
| * there are at most four threads involved, and because the |
| * updates are only once every few jiffies, the probability of |
| * lossage (and thus of slight grace-period extension) is |
| * quite low. |
| * |
| * Note that if the jiffies_till_sched_qs boot/sysfs parameter |
| * is set too high, we override with half of the RCU CPU stall |
| * warning delay. |
| */ |
| rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu); |
| if (!READ_ONCE(*rnhqp) && |
| (time_after(jiffies, rdp->rsp->gp_start + jtsq) || |
| time_after(jiffies, rdp->rsp->jiffies_resched))) { |
| WRITE_ONCE(*rnhqp, true); |
| /* Store rcu_need_heavy_qs before rcu_urgent_qs. */ |
| smp_store_release(ruqp, true); |
| rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */ |
| } |
| |
| /* |
| * If more than halfway to RCU CPU stall-warning time, do |
| * a resched_cpu() to try to loosen things up a bit. |
| */ |
| if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) |
| resched_cpu(rdp->cpu); |
| |
| return 0; |
| } |
| |
| static void record_gp_stall_check_time(struct rcu_state *rsp) |
| { |
| unsigned long j = jiffies; |
| unsigned long j1; |
| |
| rsp->gp_start = j; |
| smp_wmb(); /* Record start time before stall time. */ |
| j1 = rcu_jiffies_till_stall_check(); |
| WRITE_ONCE(rsp->jiffies_stall, j + j1); |
| rsp->jiffies_resched = j + j1 / 2; |
| rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs); |
| } |
| |
| /* |
| * Convert a ->gp_state value to a character string. |
| */ |
| static const char *gp_state_getname(short gs) |
| { |
| if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) |
| return "???"; |
| return gp_state_names[gs]; |
| } |
| |
| /* |
| * Complain about starvation of grace-period kthread. |
| */ |
| static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp) |
| { |
| unsigned long gpa; |
| unsigned long j; |
| |
| j = jiffies; |
| gpa = READ_ONCE(rsp->gp_activity); |
| if (j - gpa > 2 * HZ) { |
| pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx ->cpu=%d\n", |
| rsp->name, j - gpa, |
| rsp->gpnum, rsp->completed, |
| rsp->gp_flags, |
| gp_state_getname(rsp->gp_state), rsp->gp_state, |
| rsp->gp_kthread ? rsp->gp_kthread->state : ~0, |
| rsp->gp_kthread ? task_cpu(rsp->gp_kthread) : -1); |
| if (rsp->gp_kthread) { |
| sched_show_task(rsp->gp_kthread); |
| wake_up_process(rsp->gp_kthread); |
| } |
| } |
| } |
| |
| /* |
| * Dump stacks of all tasks running on stalled CPUs. First try using |
| * NMIs, but fall back to manual remote stack tracing on architectures |
| * that don't support NMI-based stack dumps. The NMI-triggered stack |
| * traces are more accurate because they are printed by the target CPU. |
| */ |
| static void rcu_dump_cpu_stacks(struct rcu_state *rsp) |
| { |
| int cpu; |
| unsigned long flags; |
| struct rcu_node *rnp; |
| |
| rcu_for_each_leaf_node(rsp, rnp) { |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| for_each_leaf_node_possible_cpu(rnp, cpu) |
| if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) |
| if (!trigger_single_cpu_backtrace(cpu)) |
| dump_cpu_task(cpu); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| } |
| |
| /* |
| * If too much time has passed in the current grace period, and if |
| * so configured, go kick the relevant kthreads. |
| */ |
| static void rcu_stall_kick_kthreads(struct rcu_state *rsp) |
| { |
| unsigned long j; |
| |
| if (!rcu_kick_kthreads) |
| return; |
| j = READ_ONCE(rsp->jiffies_kick_kthreads); |
| if (time_after(jiffies, j) && rsp->gp_kthread && |
| (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) { |
| WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name); |
| rcu_ftrace_dump(DUMP_ALL); |
| wake_up_process(rsp->gp_kthread); |
| WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ); |
| } |
| } |
| |
| static inline void panic_on_rcu_stall(void) |
| { |
| if (sysctl_panic_on_rcu_stall) |
| panic("RCU Stall\n"); |
| } |
| |
| static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum) |
| { |
| int cpu; |
| long delta; |
| unsigned long flags; |
| unsigned long gpa; |
| unsigned long j; |
| int ndetected = 0; |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| long totqlen = 0; |
| |
| /* Kick and suppress, if so configured. */ |
| rcu_stall_kick_kthreads(rsp); |
| if (rcu_cpu_stall_suppress) |
| return; |
| |
| /* Only let one CPU complain about others per time interval. */ |
| |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| delta = jiffies - READ_ONCE(rsp->jiffies_stall); |
| if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| WRITE_ONCE(rsp->jiffies_stall, |
| jiffies + 3 * rcu_jiffies_till_stall_check() + 3); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| |
| /* |
| * OK, time to rat on our buddy... |
| * See Documentation/RCU/stallwarn.txt for info on how to debug |
| * RCU CPU stall warnings. |
| */ |
| pr_err("INFO: %s detected stalls on CPUs/tasks:", |
| rsp->name); |
| print_cpu_stall_info_begin(); |
| rcu_for_each_leaf_node(rsp, rnp) { |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| ndetected += rcu_print_task_stall(rnp); |
| if (rnp->qsmask != 0) { |
| for_each_leaf_node_possible_cpu(rnp, cpu) |
| if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { |
| print_cpu_stall_info(rsp, cpu); |
| ndetected++; |
| } |
| } |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| |
| print_cpu_stall_info_end(); |
| for_each_possible_cpu(cpu) |
| totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda, |
| cpu)->cblist); |
| pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n", |
| smp_processor_id(), (long)(jiffies - rsp->gp_start), |
| (long)rsp->gpnum, (long)rsp->completed, totqlen); |
| if (ndetected) { |
| rcu_dump_cpu_stacks(rsp); |
| |
| /* Complain about tasks blocking the grace period. */ |
| rcu_print_detail_task_stall(rsp); |
| } else { |
| if (READ_ONCE(rsp->gpnum) != gpnum || |
| READ_ONCE(rsp->completed) == gpnum) { |
| pr_err("INFO: Stall ended before state dump start\n"); |
| } else { |
| j = jiffies; |
| gpa = READ_ONCE(rsp->gp_activity); |
| pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", |
| rsp->name, j - gpa, j, gpa, |
| jiffies_till_next_fqs, |
| rcu_get_root(rsp)->qsmask); |
| /* In this case, the current CPU might be at fault. */ |
| sched_show_task(current); |
| } |
| } |
| |
| rcu_check_gp_kthread_starvation(rsp); |
| |
| panic_on_rcu_stall(); |
| |
| force_quiescent_state(rsp); /* Kick them all. */ |
| } |
| |
| static void print_cpu_stall(struct rcu_state *rsp) |
| { |
| int cpu; |
| unsigned long flags; |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| long totqlen = 0; |
| |
| /* Kick and suppress, if so configured. */ |
| rcu_stall_kick_kthreads(rsp); |
| if (rcu_cpu_stall_suppress) |
| return; |
| |
| /* |
| * OK, time to rat on ourselves... |
| * See Documentation/RCU/stallwarn.txt for info on how to debug |
| * RCU CPU stall warnings. |
| */ |
| pr_err("INFO: %s self-detected stall on CPU", rsp->name); |
| print_cpu_stall_info_begin(); |
| print_cpu_stall_info(rsp, smp_processor_id()); |
| print_cpu_stall_info_end(); |
| for_each_possible_cpu(cpu) |
| totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda, |
| cpu)->cblist); |
| pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n", |
| jiffies - rsp->gp_start, |
| (long)rsp->gpnum, (long)rsp->completed, totqlen); |
| |
| rcu_check_gp_kthread_starvation(rsp); |
| |
| rcu_dump_cpu_stacks(rsp); |
| |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall))) |
| WRITE_ONCE(rsp->jiffies_stall, |
| jiffies + 3 * rcu_jiffies_till_stall_check() + 3); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| |
| panic_on_rcu_stall(); |
| |
| /* |
| * Attempt to revive the RCU machinery by forcing a context switch. |
| * |
| * A context switch would normally allow the RCU state machine to make |
| * progress and it could be we're stuck in kernel space without context |
| * switches for an entirely unreasonable amount of time. |
| */ |
| resched_cpu(smp_processor_id()); |
| } |
| |
| static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| unsigned long completed; |
| unsigned long gpnum; |
| unsigned long gps; |
| unsigned long j; |
| unsigned long js; |
| struct rcu_node *rnp; |
| |
| if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) || |
| !rcu_gp_in_progress(rsp)) |
| return; |
| rcu_stall_kick_kthreads(rsp); |
| j = jiffies; |
| |
| /* |
| * Lots of memory barriers to reject false positives. |
| * |
| * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall, |
| * then rsp->gp_start, and finally rsp->completed. These values |
| * are updated in the opposite order with memory barriers (or |
| * equivalent) during grace-period initialization and cleanup. |
| * Now, a false positive can occur if we get an new value of |
| * rsp->gp_start and a old value of rsp->jiffies_stall. But given |
| * the memory barriers, the only way that this can happen is if one |
| * grace period ends and another starts between these two fetches. |
| * Detect this by comparing rsp->completed with the previous fetch |
| * from rsp->gpnum. |
| * |
| * Given this check, comparisons of jiffies, rsp->jiffies_stall, |
| * and rsp->gp_start suffice to forestall false positives. |
| */ |
| gpnum = READ_ONCE(rsp->gpnum); |
| smp_rmb(); /* Pick up ->gpnum first... */ |
| js = READ_ONCE(rsp->jiffies_stall); |
| smp_rmb(); /* ...then ->jiffies_stall before the rest... */ |
| gps = READ_ONCE(rsp->gp_start); |
| smp_rmb(); /* ...and finally ->gp_start before ->completed. */ |
| completed = READ_ONCE(rsp->completed); |
| if (ULONG_CMP_GE(completed, gpnum) || |
| ULONG_CMP_LT(j, js) || |
| ULONG_CMP_GE(gps, js)) |
| return; /* No stall or GP completed since entering function. */ |
| rnp = rdp->mynode; |
| if (rcu_gp_in_progress(rsp) && |
| (READ_ONCE(rnp->qsmask) & rdp->grpmask)) { |
| |
| /* We haven't checked in, so go dump stack. */ |
| print_cpu_stall(rsp); |
| |
| } else if (rcu_gp_in_progress(rsp) && |
| ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) { |
| |
| /* They had a few time units to dump stack, so complain. */ |
| print_other_cpu_stall(rsp, gpnum); |
| } |
| } |
| |
| /** |
| * rcu_cpu_stall_reset - prevent further stall warnings in current grace period |
| * |
| * Set the stall-warning timeout way off into the future, thus preventing |
| * any RCU CPU stall-warning messages from appearing in the current set of |
| * RCU grace periods. |
| * |
| * The caller must disable hard irqs. |
| */ |
| void rcu_cpu_stall_reset(void) |
| { |
| struct rcu_state *rsp; |
| |
| for_each_rcu_flavor(rsp) |
| WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2); |
| } |
| |
| /* |
| * Determine the value that ->completed will have at the end of the |
| * next subsequent grace period. This is used to tag callbacks so that |
| * a CPU can invoke callbacks in a timely fashion even if that CPU has |
| * been dyntick-idle for an extended period with callbacks under the |
| * influence of RCU_FAST_NO_HZ. |
| * |
| * The caller must hold rnp->lock with interrupts disabled. |
| */ |
| static unsigned long rcu_cbs_completed(struct rcu_state *rsp, |
| struct rcu_node *rnp) |
| { |
| lockdep_assert_held(&rnp->lock); |
| |
| /* |
| * If RCU is idle, we just wait for the next grace period. |
| * But we can only be sure that RCU is idle if we are looking |
| * at the root rcu_node structure -- otherwise, a new grace |
| * period might have started, but just not yet gotten around |
| * to initializing the current non-root rcu_node structure. |
| */ |
| if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed) |
| return rnp->completed + 1; |
| |
| /* |
| * Otherwise, wait for a possible partial grace period and |
| * then the subsequent full grace period. |
| */ |
| return rnp->completed + 2; |
| } |
| |
| /* |
| * Trace-event helper function for rcu_start_future_gp() and |
| * rcu_nocb_wait_gp(). |
| */ |
| static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, |
| unsigned long c, const char *s) |
| { |
| trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, |
| rnp->completed, c, rnp->level, |
| rnp->grplo, rnp->grphi, s); |
| } |
| |
| /* |
| * Start some future grace period, as needed to handle newly arrived |
| * callbacks. The required future grace periods are recorded in each |
| * rcu_node structure's ->need_future_gp field. Returns true if there |
| * is reason to awaken the grace-period kthread. |
| * |
| * The caller must hold the specified rcu_node structure's ->lock. |
| */ |
| static bool __maybe_unused |
| rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, |
| unsigned long *c_out) |
| { |
| unsigned long c; |
| bool ret = false; |
| struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); |
| |
| lockdep_assert_held(&rnp->lock); |
| |
| /* |
| * Pick up grace-period number for new callbacks. If this |
| * grace period is already marked as needed, return to the caller. |
| */ |
| c = rcu_cbs_completed(rdp->rsp, rnp); |
| trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf")); |
| if (rnp->need_future_gp[c & 0x1]) { |
| trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf")); |
| goto out; |
| } |
| |
| /* |
| * If either this rcu_node structure or the root rcu_node structure |
| * believe that a grace period is in progress, then we must wait |
| * for the one following, which is in "c". Because our request |
| * will be noticed at the end of the current grace period, we don't |
| * need to explicitly start one. We only do the lockless check |
| * of rnp_root's fields if the current rcu_node structure thinks |
| * there is no grace period in flight, and because we hold rnp->lock, |
| * the only possible change is when rnp_root's two fields are |
| * equal, in which case rnp_root->gpnum might be concurrently |
| * incremented. But that is OK, as it will just result in our |
| * doing some extra useless work. |
| */ |
| if (rnp->gpnum != rnp->completed || |
| READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) { |
| rnp->need_future_gp[c & 0x1]++; |
| trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf")); |
| goto out; |
| } |
| |
| /* |
| * There might be no grace period in progress. If we don't already |
| * hold it, acquire the root rcu_node structure's lock in order to |
| * start one (if needed). |
| */ |
| if (rnp != rnp_root) |
| raw_spin_lock_rcu_node(rnp_root); |
| |
| /* |
| * Get a new grace-period number. If there really is no grace |
| * period in progress, it will be smaller than the one we obtained |
| * earlier. Adjust callbacks as needed. |
| */ |
| c = rcu_cbs_completed(rdp->rsp, rnp_root); |
| if (!rcu_is_nocb_cpu(rdp->cpu)) |
| (void)rcu_segcblist_accelerate(&rdp->cblist, c); |
| |
| /* |
| * If the needed for the required grace period is already |
| * recorded, trace and leave. |
| */ |
| if (rnp_root->need_future_gp[c & 0x1]) { |
| trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot")); |
| goto unlock_out; |
| } |
| |
| /* Record the need for the future grace period. */ |
| rnp_root->need_future_gp[c & 0x1]++; |
| |
| /* If a grace period is not already in progress, start one. */ |
| if (rnp_root->gpnum != rnp_root->completed) { |
| trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot")); |
| } else { |
| trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot")); |
| ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp); |
| } |
| unlock_out: |
| if (rnp != rnp_root) |
| raw_spin_unlock_rcu_node(rnp_root); |
| out: |
| if (c_out != NULL) |
| *c_out = c; |
| return ret; |
| } |
| |
| /* |
| * Clean up any old requests for the just-ended grace period. Also return |
| * whether any additional grace periods have been requested. |
| */ |
| static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
| { |
| int c = rnp->completed; |
| int needmore; |
| struct rcu_data *rdp = this_cpu_ptr(rsp->rda); |
| |
| rnp->need_future_gp[c & 0x1] = 0; |
| needmore = rnp->need_future_gp[(c + 1) & 0x1]; |
| trace_rcu_future_gp(rnp, rdp, c, |
| needmore ? TPS("CleanupMore") : TPS("Cleanup")); |
| return needmore; |
| } |
| |
| /* |
| * Awaken the grace-period kthread for the specified flavor of RCU. |
| * Don't do a self-awaken, and don't bother awakening when there is |
| * nothing for the grace-period kthread to do (as in several CPUs |
| * raced to awaken, and we lost), and finally don't try to awaken |
| * a kthread that has not yet been created. |
| */ |
| static void rcu_gp_kthread_wake(struct rcu_state *rsp) |
| { |
| if (current == rsp->gp_kthread || |
| !READ_ONCE(rsp->gp_flags) || |
| !rsp->gp_kthread) |
| return; |
| swake_up(&rsp->gp_wq); |
| } |
| |
| /* |
| * If there is room, assign a ->completed number to any callbacks on |
| * this CPU that have not already been assigned. Also accelerate any |
| * callbacks that were previously assigned a ->completed number that has |
| * since proven to be too conservative, which can happen if callbacks get |
| * assigned a ->completed number while RCU is idle, but with reference to |
| * a non-root rcu_node structure. This function is idempotent, so it does |
| * not hurt to call it repeatedly. Returns an flag saying that we should |
| * awaken the RCU grace-period kthread. |
| * |
| * The caller must hold rnp->lock with interrupts disabled. |
| */ |
| static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| bool ret = false; |
| |
| lockdep_assert_held(&rnp->lock); |
| |
| /* If no pending (not yet ready to invoke) callbacks, nothing to do. */ |
| if (!rcu_segcblist_pend_cbs(&rdp->cblist)) |
| return false; |
| |
| /* |
| * Callbacks are often registered with incomplete grace-period |
| * information. Something about the fact that getting exact |
| * information requires acquiring a global lock... RCU therefore |
| * makes a conservative estimate of the grace period number at which |
| * a given callback will become ready to invoke. The following |
| * code checks this estimate and improves it when possible, thus |
| * accelerating callback invocation to an earlier grace-period |
| * number. |
| */ |
| if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp))) |
| ret = rcu_start_future_gp(rnp, rdp, NULL); |
| |
| /* Trace depending on how much we were able to accelerate. */ |
| if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL)) |
| trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB")); |
| else |
| trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB")); |
| return ret; |
| } |
| |
| /* |
| * Move any callbacks whose grace period has completed to the |
| * RCU_DONE_TAIL sublist, then compact the remaining sublists and |
| * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL |
| * sublist. This function is idempotent, so it does not hurt to |
| * invoke it repeatedly. As long as it is not invoked -too- often... |
| * Returns true if the RCU grace-period kthread needs to be awakened. |
| * |
| * The caller must hold rnp->lock with interrupts disabled. |
| */ |
| static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| lockdep_assert_held(&rnp->lock); |
| |
| /* If no pending (not yet ready to invoke) callbacks, nothing to do. */ |
| if (!rcu_segcblist_pend_cbs(&rdp->cblist)) |
| return false; |
| |
| /* |
| * Find all callbacks whose ->completed numbers indicate that they |
| * are ready to invoke, and put them into the RCU_DONE_TAIL sublist. |
| */ |
| rcu_segcblist_advance(&rdp->cblist, rnp->completed); |
| |
| /* Classify any remaining callbacks. */ |
| return rcu_accelerate_cbs(rsp, rnp, rdp); |
| } |
| |
| /* |
| * Update CPU-local rcu_data state to record the beginnings and ends of |
| * grace periods. The caller must hold the ->lock of the leaf rcu_node |
| * structure corresponding to the current CPU, and must have irqs disabled. |
| * Returns true if the grace-period kthread needs to be awakened. |
| */ |
| static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| bool ret; |
| bool need_gp; |
| |
| lockdep_assert_held(&rnp->lock); |
| |
| /* Handle the ends of any preceding grace periods first. */ |
| if (rdp->completed == rnp->completed && |
| !unlikely(READ_ONCE(rdp->gpwrap))) { |
| |
| /* No grace period end, so just accelerate recent callbacks. */ |
| ret = rcu_accelerate_cbs(rsp, rnp, rdp); |
| |
| } else { |
| |
| /* Advance callbacks. */ |
| ret = rcu_advance_cbs(rsp, rnp, rdp); |
| |
| /* Remember that we saw this grace-period completion. */ |
| rdp->completed = rnp->completed; |
| trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend")); |
| } |
| |
| if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) { |
| /* |
| * If the current grace period is waiting for this CPU, |
| * set up to detect a quiescent state, otherwise don't |
| * go looking for one. |
| */ |
| rdp->gpnum = rnp->gpnum; |
| trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart")); |
| need_gp = !!(rnp->qsmask & rdp->grpmask); |
| rdp->cpu_no_qs.b.norm = need_gp; |
| rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr); |
| rdp->core_needs_qs = need_gp; |
| zero_cpu_stall_ticks(rdp); |
| WRITE_ONCE(rdp->gpwrap, false); |
| } |
| return ret; |
| } |
| |
| static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| unsigned long flags; |
| bool needwake; |
| struct rcu_node *rnp; |
| |
| local_irq_save(flags); |
| rnp = rdp->mynode; |
| if ((rdp->gpnum == READ_ONCE(rnp->gpnum) && |
| rdp->completed == READ_ONCE(rnp->completed) && |
| !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */ |
| !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */ |
| local_irq_restore(flags); |
| return; |
| } |
| needwake = __note_gp_changes(rsp, rnp, rdp); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| if (needwake) |
| rcu_gp_kthread_wake(rsp); |
| } |
| |
| static void rcu_gp_slow(struct rcu_state *rsp, int delay) |
| { |
| if (delay > 0 && |
| !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) |
| schedule_timeout_uninterruptible(delay); |
| } |
| |
| /* |
| * Initialize a new grace period. Return false if no grace period required. |
| */ |
| static bool rcu_gp_init(struct rcu_state *rsp) |
| { |
| unsigned long oldmask; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| raw_spin_lock_irq_rcu_node(rnp); |
| if (!READ_ONCE(rsp->gp_flags)) { |
| /* Spurious wakeup, tell caller to go back to sleep. */ |
| raw_spin_unlock_irq_rcu_node(rnp); |
| return false; |
| } |
| WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */ |
| |
| if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) { |
| /* |
| * Grace period already in progress, don't start another. |
| * Not supposed to be able to happen. |
| */ |
| raw_spin_unlock_irq_rcu_node(rnp); |
| return false; |
| } |
| |
| /* Advance to a new grace period and initialize state. */ |
| record_gp_stall_check_time(rsp); |
| /* Record GP times before starting GP, hence smp_store_release(). */ |
| smp_store_release(&rsp->gpnum, rsp->gpnum + 1); |
| trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start")); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| |
| /* |
| * Apply per-leaf buffered online and offline operations to the |
| * rcu_node tree. Note that this new grace period need not wait |
| * for subsequent online CPUs, and that quiescent-state forcing |
| * will handle subsequent offline CPUs. |
| */ |
| rcu_for_each_leaf_node(rsp, rnp) { |
| rcu_gp_slow(rsp, gp_preinit_delay); |
| raw_spin_lock_irq_rcu_node(rnp); |
| if (rnp->qsmaskinit == rnp->qsmaskinitnext && |
| !rnp->wait_blkd_tasks) { |
| /* Nothing to do on this leaf rcu_node structure. */ |
| raw_spin_unlock_irq_rcu_node(rnp); |
| continue; |
| } |
| |
| /* Record old state, apply changes to ->qsmaskinit field. */ |
| oldmask = rnp->qsmaskinit; |
| rnp->qsmaskinit = rnp->qsmaskinitnext; |
| |
| /* If zero-ness of ->qsmaskinit changed, propagate up tree. */ |
| if (!oldmask != !rnp->qsmaskinit) { |
| if (!oldmask) /* First online CPU for this rcu_node. */ |
| rcu_init_new_rnp(rnp); |
| else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */ |
| rnp->wait_blkd_tasks = true; |
| else /* Last offline CPU and can propagate. */ |
| rcu_cleanup_dead_rnp(rnp); |
| } |
| |
| /* |
| * If all waited-on tasks from prior grace period are |
| * done, and if all this rcu_node structure's CPUs are |
| * still offline, propagate up the rcu_node tree and |
| * clear ->wait_blkd_tasks. Otherwise, if one of this |
| * rcu_node structure's CPUs has since come back online, |
| * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp() |
| * checks for this, so just call it unconditionally). |
| */ |
| if (rnp->wait_blkd_tasks && |
| (!rcu_preempt_has_tasks(rnp) || |
| rnp->qsmaskinit)) { |
| rnp->wait_blkd_tasks = false; |
| rcu_cleanup_dead_rnp(rnp); |
| } |
| |
| raw_spin_unlock_irq_rcu_node(rnp); |
| } |
| |
| /* |
| * Set the quiescent-state-needed bits in all the rcu_node |
| * structures for all currently online CPUs in breadth-first order, |
| * starting from the root rcu_node structure, relying on the layout |
| * of the tree within the rsp->node[] array. Note that other CPUs |
| * will access only the leaves of the hierarchy, thus seeing that no |
| * grace period is in progress, at least until the corresponding |
| * leaf node has been initialized. |
| * |
| * The grace period cannot complete until the initialization |
| * process finishes, because this kthread handles both. |
| */ |
| rcu_for_each_node_breadth_first(rsp, rnp) { |
| rcu_gp_slow(rsp, gp_init_delay); |
| raw_spin_lock_irq_rcu_node(rnp); |
| rdp = this_cpu_ptr(rsp->rda); |
| rcu_preempt_check_blocked_tasks(rnp); |
| rnp->qsmask = rnp->qsmaskinit; |
| WRITE_ONCE(rnp->gpnum, rsp->gpnum); |
| if (WARN_ON_ONCE(rnp->completed != rsp->completed)) |
| WRITE_ONCE(rnp->completed, rsp->completed); |
| if (rnp == rdp->mynode) |
| (void)__note_gp_changes(rsp, rnp, rdp); |
| rcu_preempt_boost_start_gp(rnp); |
| trace_rcu_grace_period_init(rsp->name, rnp->gpnum, |
| rnp->level, rnp->grplo, |
| rnp->grphi, rnp->qsmask); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| cond_resched_rcu_qs(); |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| } |
| |
| return true; |
| } |
| |
| /* |
| * Helper function for swait_event_idle() wakeup at force-quiescent-state |
| * time. |
| */ |
| static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp) |
| { |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| |
| /* Someone like call_rcu() requested a force-quiescent-state scan. */ |
| *gfp = READ_ONCE(rsp->gp_flags); |
| if (*gfp & RCU_GP_FLAG_FQS) |
| return true; |
| |
| /* The current grace period has completed. */ |
| if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) |
| return true; |
| |
| return false; |
| } |
| |
| /* |
| * Do one round of quiescent-state forcing. |
| */ |
| static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time) |
| { |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| rsp->n_force_qs++; |
| if (first_time) { |
| /* Collect dyntick-idle snapshots. */ |
| force_qs_rnp(rsp, dyntick_save_progress_counter); |
| } else { |
| /* Handle dyntick-idle and offline CPUs. */ |
| force_qs_rnp(rsp, rcu_implicit_dynticks_qs); |
| } |
| /* Clear flag to prevent immediate re-entry. */ |
| if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { |
| raw_spin_lock_irq_rcu_node(rnp); |
| WRITE_ONCE(rsp->gp_flags, |
| READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| } |
| } |
| |
| /* |
| * Clean up after the old grace period. |
| */ |
| static void rcu_gp_cleanup(struct rcu_state *rsp) |
| { |
| unsigned long gp_duration; |
| bool needgp = false; |
| int nocb = 0; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| struct swait_queue_head *sq; |
| |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| raw_spin_lock_irq_rcu_node(rnp); |
| gp_duration = jiffies - rsp->gp_start; |
| if (gp_duration > rsp->gp_max) |
| rsp->gp_max = gp_duration; |
| |
| /* |
| * We know the grace period is complete, but to everyone else |
| * it appears to still be ongoing. But it is also the case |
| * that to everyone else it looks like there is nothing that |
| * they can do to advance the grace period. It is therefore |
| * safe for us to drop the lock in order to mark the grace |
| * period as completed in all of the rcu_node structures. |
| */ |
| raw_spin_unlock_irq_rcu_node(rnp); |
| |
| /* |
| * Propagate new ->completed value to rcu_node structures so |
| * that other CPUs don't have to wait until the start of the next |
| * grace period to process their callbacks. This also avoids |
| * some nasty RCU grace-period initialization races by forcing |
| * the end of the current grace period to be completely recorded in |
| * all of the rcu_node structures before the beginning of the next |
| * grace period is recorded in any of the rcu_node structures. |
| */ |
| rcu_for_each_node_breadth_first(rsp, rnp) { |
| raw_spin_lock_irq_rcu_node(rnp); |
| WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
| WARN_ON_ONCE(rnp->qsmask); |
| WRITE_ONCE(rnp->completed, rsp->gpnum); |
| rdp = this_cpu_ptr(rsp->rda); |
| if (rnp == rdp->mynode) |
| needgp = __note_gp_changes(rsp, rnp, rdp) || needgp; |
| /* smp_mb() provided by prior unlock-lock pair. */ |
| nocb += rcu_future_gp_cleanup(rsp, rnp); |
| sq = rcu_nocb_gp_get(rnp); |
| raw_spin_unlock_irq_rcu_node(rnp); |
| rcu_nocb_gp_cleanup(sq); |
| cond_resched_rcu_qs(); |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| rcu_gp_slow(rsp, gp_cleanup_delay); |
| } |
| rnp = rcu_get_root(rsp); |
| raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */ |
| rcu_nocb_gp_set(rnp, nocb); |
| |
| /* Declare grace period done. */ |
| WRITE_ONCE(rsp->completed, rsp->gpnum); |
| trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end")); |
| rsp->gp_state = RCU_GP_IDLE; |
| rdp = this_cpu_ptr(rsp->rda); |
| /* Advance CBs to reduce false positives below. */ |
| needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp; |
| if (needgp || cpu_needs_another_gp(rsp, rdp)) { |
| WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("newreq")); |
| } |
| raw_spin_unlock_irq_rcu_node(rnp); |
| } |
| |
| /* |
| * Body of kthread that handles grace periods. |
| */ |
| static int __noreturn rcu_gp_kthread(void *arg) |
| { |
| bool first_gp_fqs; |
| int gf; |
| unsigned long j; |
| int ret; |
| struct rcu_state *rsp = arg; |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| |
| rcu_bind_gp_kthread(); |
| for (;;) { |
| |
| /* Handle grace-period start. */ |
| for (;;) { |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("reqwait")); |
| rsp->gp_state = RCU_GP_WAIT_GPS; |
| swait_event_idle(rsp->gp_wq, READ_ONCE(rsp->gp_flags) & |
| RCU_GP_FLAG_INIT); |
| rsp->gp_state = RCU_GP_DONE_GPS; |
| /* Locking provides needed memory barrier. */ |
| if (rcu_gp_init(rsp)) |
| break; |
| cond_resched_rcu_qs(); |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| WARN_ON(signal_pending(current)); |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("reqwaitsig")); |
| } |
| |
| /* Handle quiescent-state forcing. */ |
| first_gp_fqs = true; |
| j = jiffies_till_first_fqs; |
| if (j > HZ) { |
| j = HZ; |
| jiffies_till_first_fqs = HZ; |
| } |
| ret = 0; |
| for (;;) { |
| if (!ret) { |
| rsp->jiffies_force_qs = jiffies + j; |
| WRITE_ONCE(rsp->jiffies_kick_kthreads, |
| jiffies + 3 * j); |
| } |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("fqswait")); |
| rsp->gp_state = RCU_GP_WAIT_FQS; |
| ret = swait_event_idle_timeout(rsp->gp_wq, |
| rcu_gp_fqs_check_wake(rsp, &gf), j); |
| rsp->gp_state = RCU_GP_DOING_FQS; |
| /* Locking provides needed memory barriers. */ |
| /* If grace period done, leave loop. */ |
| if (!READ_ONCE(rnp->qsmask) && |
| !rcu_preempt_blocked_readers_cgp(rnp)) |
| break; |
| /* If time for quiescent-state forcing, do it. */ |
| if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) || |
| (gf & RCU_GP_FLAG_FQS)) { |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("fqsstart")); |
| rcu_gp_fqs(rsp, first_gp_fqs); |
| first_gp_fqs = false; |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("fqsend")); |
| cond_resched_rcu_qs(); |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| ret = 0; /* Force full wait till next FQS. */ |
| j = jiffies_till_next_fqs; |
| if (j > HZ) { |
| j = HZ; |
| jiffies_till_next_fqs = HZ; |
| } else if (j < 1) { |
| j = 1; |
| jiffies_till_next_fqs = 1; |
| } |
| } else { |
| /* Deal with stray signal. */ |
| cond_resched_rcu_qs(); |
| WRITE_ONCE(rsp->gp_activity, jiffies); |
| WARN_ON(signal_pending(current)); |
| trace_rcu_grace_period(rsp->name, |
| READ_ONCE(rsp->gpnum), |
| TPS("fqswaitsig")); |
| ret = 1; /* Keep old FQS timing. */ |
| j = jiffies; |
| if (time_after(jiffies, rsp->jiffies_force_qs)) |
| j = 1; |
| else |
| j = rsp->jiffies_force_qs - j; |
| } |
| } |
| |
| /* Handle grace-period end. */ |
| rsp->gp_state = RCU_GP_CLEANUP; |
| rcu_gp_cleanup(rsp); |
| rsp->gp_state = RCU_GP_CLEANED; |
| } |
| } |
| |
| /* |
| * Start a new RCU grace period if warranted, re-initializing the hierarchy |
| * in preparation for detecting the next grace period. The caller must hold |
| * the root node's ->lock and hard irqs must be disabled. |
| * |
| * Note that it is legal for a dying CPU (which is marked as offline) to |
| * invoke this function. This can happen when the dying CPU reports its |
| * quiescent state. |
| * |
| * Returns true if the grace-period kthread must be awakened. |
| */ |
| static bool |
| rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| lockdep_assert_held(&rnp->lock); |
| if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { |
| /* |
| * Either we have not yet spawned the grace-period |
| * task, this CPU does not need another grace period, |
| * or a grace period is already in progress. |
| * Either way, don't start a new grace period. |
| */ |
| return false; |
| } |
| WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); |
| trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), |
| TPS("newreq")); |
| |
| /* |
| * We can't do wakeups while holding the rnp->lock, as that |
| * could cause possible deadlocks with the rq->lock. Defer |
| * the wakeup to our caller. |
| */ |
| return true; |
| } |
| |
| /* |
| * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's |
| * callbacks. Note that rcu_start_gp_advanced() cannot do this because it |
| * is invoked indirectly from rcu_advance_cbs(), which would result in |
| * endless recursion -- or would do so if it wasn't for the self-deadlock |
| * that is encountered beforehand. |
| * |
| * Returns true if the grace-period kthread needs to be awakened. |
| */ |
| static bool rcu_start_gp(struct rcu_state *rsp) |
| { |
| struct rcu_data *rdp = this_cpu_ptr(rsp->rda); |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| bool ret = false; |
| |
| /* |
| * If there is no grace period in progress right now, any |
| * callbacks we have up to this point will be satisfied by the |
| * next grace period. Also, advancing the callbacks reduces the |
| * probability of false positives from cpu_needs_another_gp() |
| * resulting in pointless grace periods. So, advance callbacks |
| * then start the grace period! |
| */ |
| ret = rcu_advance_cbs(rsp, rnp, rdp) || ret; |
| ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret; |
| return ret; |
| } |
| |
| /* |
| * Report a full set of quiescent states to the specified rcu_state data |
| * structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period |
| * kthread if another grace period is required. Whether we wake |
| * the grace-period kthread or it awakens itself for the next round |
| * of quiescent-state forcing, that kthread will clean up after the |
| * just-completed grace period. Note that the caller must hold rnp->lock, |
| * which is released before return. |
| */ |
| static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) |
| __releases(rcu_get_root(rsp)->lock) |
| { |
| lockdep_assert_held(&rcu_get_root(rsp)->lock); |
| WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); |
| WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); |
| raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags); |
| rcu_gp_kthread_wake(rsp); |
| } |
| |
| /* |
| * Similar to rcu_report_qs_rdp(), for which it is a helper function. |
| * Allows quiescent states for a group of CPUs to be reported at one go |
| * to the specified rcu_node structure, though all the CPUs in the group |
| * must be represented by the same rcu_node structure (which need not be a |
| * leaf rcu_node structure, though it often will be). The gps parameter |
| * is the grace-period snapshot, which means that the quiescent states |
| * are valid only if rnp->gpnum is equal to gps. That structure's lock |
| * must be held upon entry, and it is released before return. |
| */ |
| static void |
| rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, |
| struct rcu_node *rnp, unsigned long gps, unsigned long flags) |
| __releases(rnp->lock) |
| { |
| unsigned long oldmask = 0; |
| struct rcu_node *rnp_c; |
| |
| lockdep_assert_held(&rnp->lock); |
| |
| /* Walk up the rcu_node hierarchy. */ |
| for (;;) { |
| if (!(rnp->qsmask & mask) || rnp->gpnum != gps) { |
| |
| /* |
| * Our bit has already been cleared, or the |
| * relevant grace period is already over, so done. |
| */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */ |
| WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1 && |
| rcu_preempt_blocked_readers_cgp(rnp)); |
| rnp->qsmask &= ~mask; |
| trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum, |
| mask, rnp->qsmask, rnp->level, |
| rnp->grplo, rnp->grphi, |
| !!rnp->gp_tasks); |
| if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
| |
| /* Other bits still set at this level, so done. */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| mask = rnp->grpmask; |
| if (rnp->parent == NULL) { |
| |
| /* No more levels. Exit loop holding root lock. */ |
| |
| break; |
| } |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| rnp_c = rnp; |
| rnp = rnp->parent; |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| oldmask = rnp_c->qsmask; |
| } |
| |
| /* |
| * Get here if we are the last CPU to pass through a quiescent |
| * state for this grace period. Invoke rcu_report_qs_rsp() |
| * to clean up and start the next grace period if one is needed. |
| */ |
| rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */ |
| } |
| |
| /* |
| * Record a quiescent state for all tasks that were previously queued |
| * on the specified rcu_node structure and that were blocking the current |
| * RCU grace period. The caller must hold the specified rnp->lock with |
| * irqs disabled, and this lock is released upon return, but irqs remain |
| * disabled. |
| */ |
| static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp, |
| struct rcu_node *rnp, unsigned long flags) |
| __releases(rnp->lock) |
| { |
| unsigned long gps; |
| unsigned long mask; |
| struct rcu_node *rnp_p; |
| |
| lockdep_assert_held(&rnp->lock); |
| if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p || |
| rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; /* Still need more quiescent states! */ |
| } |
| |
| rnp_p = rnp->parent; |
| if (rnp_p == NULL) { |
| /* |
| * Only one rcu_node structure in the tree, so don't |
| * try to report up to its nonexistent parent! |
| */ |
| rcu_report_qs_rsp(rsp, flags); |
| return; |
| } |
| |
| /* Report up the rest of the hierarchy, tracking current ->gpnum. */ |
| gps = rnp->gpnum; |
| mask = rnp->grpmask; |
| raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ |
| raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */ |
| rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags); |
| } |
| |
| /* |
| * Record a quiescent state for the specified CPU to that CPU's rcu_data |
| * structure. This must be called from the specified CPU. |
| */ |
| static void |
| rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| unsigned long flags; |
| unsigned long mask; |
| bool needwake; |
| struct rcu_node *rnp; |
| |
| rnp = rdp->mynode; |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| if (rdp->cpu_no_qs.b.norm || rdp->gpnum != rnp->gpnum || |
| rnp->completed == rnp->gpnum || rdp->gpwrap) { |
| |
| /* |
| * The grace period in which this quiescent state was |
| * recorded has ended, so don't report it upwards. |
| * We will instead need a new quiescent state that lies |
| * within the current grace period. |
| */ |
| rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */ |
| rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr); |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| return; |
| } |
| mask = rdp->grpmask; |
| if ((rnp->qsmask & mask) == 0) { |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } else { |
| rdp->core_needs_qs = false; |
| |
| /* |
| * This GP can't end until cpu checks in, so all of our |
| * callbacks can be processed during the next GP. |
| */ |
| needwake = rcu_accelerate_cbs(rsp, rnp, rdp); |
| |
| rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); |
| /* ^^^ Released rnp->lock */ |
| if (needwake) |
| rcu_gp_kthread_wake(rsp); |
| } |
| } |
| |
| /* |
| * Check to see if there is a new grace period of which this CPU |
| * is not yet aware, and if so, set up local rcu_data state for it. |
| * Otherwise, see if this CPU has just passed through its first |
| * quiescent state for this grace period, and record that fact if so. |
| */ |
| static void |
| rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| /* Check for grace-period ends and beginnings. */ |
| note_gp_changes(rsp, rdp); |
| |
| /* |
| * Does this CPU still need to do its part for current grace period? |
| * If no, return and let the other CPUs do their part as well. |
| */ |
| if (!rdp->core_needs_qs) |
| return; |
| |
| /* |
| * Was there a quiescent state since the beginning of the grace |
| * period? If no, then exit and wait for the next call. |
| */ |
| if (rdp->cpu_no_qs.b.norm) |
| return; |
| |
| /* |
| * Tell RCU we are done (but rcu_report_qs_rdp() will be the |
| * judge of that). |
| */ |
| rcu_report_qs_rdp(rdp->cpu, rsp, rdp); |
| } |
| |
| /* |
| * Trace the fact that this CPU is going offline. |
| */ |
| static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) |
| { |
| RCU_TRACE(unsigned long mask;) |
| RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);) |
| RCU_TRACE(struct rcu_node *rnp = rdp->mynode;) |
| |
| if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) |
| return; |
| |
| RCU_TRACE(mask = rdp->grpmask;) |
| trace_rcu_grace_period(rsp->name, |
| rnp->gpnum + 1 - !!(rnp->qsmask & mask), |
| TPS("cpuofl")); |
| } |
| |
| /* |
| * All CPUs for the specified rcu_node structure have gone offline, |
| * and all tasks that were preempted within an RCU read-side critical |
| * section while running on one of those CPUs have since exited their RCU |
| * read-side critical section. Some other CPU is reporting this fact with |
| * the specified rcu_node structure's ->lock held and interrupts disabled. |
| * This function therefore goes up the tree of rcu_node structures, |
| * clearing the corresponding bits in the ->qsmaskinit fields. Note that |
| * the leaf rcu_node structure's ->qsmaskinit field has already been |
| * updated |
| * |
| * This function does check that the specified rcu_node structure has |
| * all CPUs offline and no blocked tasks, so it is OK to invoke it |
| * prematurely. That said, invoking it after the fact will cost you |
| * a needless lock acquisition. So once it has done its work, don't |
| * invoke it again. |
| */ |
| static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) |
| { |
| long mask; |
| struct rcu_node *rnp = rnp_leaf; |
| |
| lockdep_assert_held(&rnp->lock); |
| if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || |
| rnp->qsmaskinit || rcu_preempt_has_tasks(rnp)) |
| return; |
| for (;;) { |
| mask = rnp->grpmask; |
| rnp = rnp->parent; |
| if (!rnp) |
| break; |
| raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
| rnp->qsmaskinit &= ~mask; |
| rnp->qsmask &= ~mask; |
| if (rnp->qsmaskinit) { |
| raw_spin_unlock_rcu_node(rnp); |
| /* irqs remain disabled. */ |
| return; |
| } |
| raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ |
| } |
| } |
| |
| /* |
| * The CPU has been completely removed, and some other CPU is reporting |
| * this fact from process context. Do the remainder of the cleanup. |
| * There can only be one CPU hotplug operation at a time, so no need for |
| * explicit locking. |
| */ |
| static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) |
| { |
| struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); |
| struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ |
| |
| if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) |
| return; |
| |
| /* Adjust any no-longer-needed kthreads. */ |
| rcu_boost_kthread_setaffinity(rnp, -1); |
| } |
| |
| /* |
| * Invoke any RCU callbacks that have made it to the end of their grace |
| * period. Thottle as specified by rdp->blimit. |
| */ |
| static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| unsigned long flags; |
| struct rcu_head *rhp; |
| struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); |
| long bl, count; |
| |
| /* If no callbacks are ready, just return. */ |
| if (!rcu_segcblist_ready_cbs(&rdp->cblist)) { |
| trace_rcu_batch_start(rsp->name, |
| rcu_segcblist_n_lazy_cbs(&rdp->cblist), |
| rcu_segcblist_n_cbs(&rdp->cblist), 0); |
| trace_rcu_batch_end(rsp->name, 0, |
| !rcu_segcblist_empty(&rdp->cblist), |
| need_resched(), is_idle_task(current), |
| rcu_is_callbacks_kthread()); |
| return; |
| } |
| |
| /* |
| * Extract the list of ready callbacks, disabling to prevent |
| * races with call_rcu() from interrupt handlers. Leave the |
| * callback counts, as rcu_barrier() needs to be conservative. |
| */ |
| local_irq_save(flags); |
| WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); |
| bl = rdp->blimit; |
| trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist), |
| rcu_segcblist_n_cbs(&rdp->cblist), bl); |
| rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl); |
| local_irq_restore(flags); |
| |
| /* Invoke callbacks. */ |
| rhp = rcu_cblist_dequeue(&rcl); |
| for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) { |
| debug_rcu_head_unqueue(rhp); |
| if (__rcu_reclaim(rsp->name, rhp)) |
| rcu_cblist_dequeued_lazy(&rcl); |
| /* |
| * Stop only if limit reached and CPU has something to do. |
| * Note: The rcl structure counts down from zero. |
| */ |
| if (-rcl.len >= bl && |
| (need_resched() || |
| (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) |
| break; |
| } |
| |
| local_irq_save(flags); |
| count = -rcl.len; |
| trace_rcu_batch_end(rsp->name, count, !!rcl.head, need_resched(), |
| is_idle_task(current), rcu_is_callbacks_kthread()); |
| |
| /* Update counts and requeue any remaining callbacks. */ |
| rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl); |
| smp_mb(); /* List handling before counting for rcu_barrier(). */ |
| rdp->n_cbs_invoked += count; |
| rcu_segcblist_insert_count(&rdp->cblist, &rcl); |
| |
| /* Reinstate batch limit if we have worked down the excess. */ |
| count = rcu_segcblist_n_cbs(&rdp->cblist); |
| if (rdp->blimit == LONG_MAX && count <= qlowmark) |
| rdp->blimit = blimit; |
| |
| /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ |
| if (count == 0 && rdp->qlen_last_fqs_check != 0) { |
| rdp->qlen_last_fqs_check = 0; |
| rdp->n_force_qs_snap = rsp->n_force_qs; |
| } else if (count < rdp->qlen_last_fqs_check - qhimark) |
| rdp->qlen_last_fqs_check = count; |
| WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0)); |
| |
| local_irq_restore(flags); |
| |
| /* Re-invoke RCU core processing if there are callbacks remaining. */ |
| if (rcu_segcblist_ready_cbs(&rdp->cblist)) |
| invoke_rcu_core(); |
| } |
| |
| /* |
| * Check to see if this CPU is in a non-context-switch quiescent state |
| * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). |
| * Also schedule RCU core processing. |
| * |
| * This function must be called from hardirq context. It is normally |
| * invoked from the scheduling-clock interrupt. |
| */ |
| void rcu_check_callbacks(int user) |
| { |
| trace_rcu_utilization(TPS("Start scheduler-tick")); |
| increment_cpu_stall_ticks(); |
| if (user || rcu_is_cpu_rrupt_from_idle()) { |
| |
| /* |
| * Get here if this CPU took its interrupt from user |
| * mode or from the idle loop, and if this is not a |
| * nested interrupt. In this case, the CPU is in |
| * a quiescent state, so note it. |
| * |
| * No memory barrier is required here because both |
| * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local |
| * variables that other CPUs neither access nor modify, |
| * at least not while the corresponding CPU is online. |
| */ |
| |
| rcu_sched_qs(); |
| rcu_bh_qs(); |
| |
| } else if (!in_softirq()) { |
| |
| /* |
| * Get here if this CPU did not take its interrupt from |
| * softirq, in other words, if it is not interrupting |
| * a rcu_bh read-side critical section. This is an _bh |
| * critical section, so note it. |
| */ |
| |
| rcu_bh_qs(); |
| } |
| rcu_preempt_check_callbacks(); |
| if (rcu_pending()) |
| invoke_rcu_core(); |
| if (user) |
| rcu_note_voluntary_context_switch(current); |
| trace_rcu_utilization(TPS("End scheduler-tick")); |
| } |
| |
| /* |
| * Scan the leaf rcu_node structures, processing dyntick state for any that |
| * have not yet encountered a quiescent state, using the function specified. |
| * Also initiate boosting for any threads blocked on the root rcu_node. |
| * |
| * The caller must have suppressed start of new grace periods. |
| */ |
| static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp)) |
| { |
| int cpu; |
| unsigned long flags; |
| unsigned long mask; |
| struct rcu_node *rnp; |
| |
| rcu_for_each_leaf_node(rsp, rnp) { |
| cond_resched_rcu_qs(); |
| mask = 0; |
| raw_spin_lock_irqsave_rcu_node(rnp, flags); |
| if (rnp->qsmask == 0) { |
| if (rcu_state_p == &rcu_sched_state || |
| rsp != rcu_state_p || |
| rcu_preempt_blocked_readers_cgp(rnp)) { |
| /* |
| * No point in scanning bits because they |
| * are all zero. But we might need to |
| * priority-boost blocked readers. |
| */ |
| rcu_initiate_boost(rnp, flags); |
| /* rcu_initiate_boost() releases rnp->lock */ |
| continue; |
| } |
| if (rnp->parent && |
| (rnp->parent->qsmask & rnp->grpmask)) { |
| /* |
| * Race between grace-period |
| * initialization and task exiting RCU |
| * read-side critical section: Report. |
| */ |
| rcu_report_unblock_qs_rnp(rsp, rnp, flags); |
| /* rcu_report_unblock_qs_rnp() rlses ->lock */ |
| continue; |
| } |
| } |
| for_each_leaf_node_possible_cpu(rnp, cpu) { |
| unsigned long bit = leaf_node_cpu_bit(rnp, cpu); |
| if ((rnp->qsmask & bit) != 0) { |
| if (f(per_cpu_ptr(rsp->rda, cpu))) |
| mask |= bit; |
| } |
| } |
| if (mask != 0) { |
| /* Idle/offline CPUs, report (releases rnp->lock. */ |
| rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); |
| } else { |
| /* Nothing to do here, so just drop the lock. */ |
| raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
| } |
| } |
| } |
| |
| /* |
| * Force quiescent states on reluctant CPUs, and also detect which |
| * CPUs are in dyntick-idle mode. |
| */ |
| static void force_quiescent_state(struct rcu_state *rsp) |
| { |
| unsigned long flags; |
| bool ret; |
| struct rcu_node *rnp; |
| struct rcu_node *rnp_old = NULL; |
| |
| /* Funnel through hierarchy to reduce memory contention. */ |
| rnp = __this_cpu_read(rsp->rda->mynode); |
| for (; rnp != NULL; rnp = rnp->parent) { |
| ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) || |
| !raw_spin_trylock(&rnp->fqslock); |
| if (rnp_old != NULL) |
| raw_spin_unlock(&rnp_old->fqslock); |
| if (ret) { |
| rsp->n_force_qs_lh++; |
| return; |
| } |
| rnp_old = rnp; |
| } |
| /* rnp_old == rcu_get_root(rsp), rnp == NULL. */ |
| |
| /* Reached the root of the rcu_node tree, acquire lock. */ |
| raw_spin_lock_irqsave_rcu_node(rnp_old, flags); |
| raw_spin_unlock(&rnp_old->fqslock); |
| if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { |
| rsp->n_force_qs_lh++; |
| raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags); |
| return; /* Someone beat us to it. */ |
| } |
| WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); |
| raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags); |
| rcu_gp_kthread_wake(rsp); |
| } |
| |
| /* |
| * This does the RCU core processing work for the specified rcu_state |
| * and rcu_data structures. This may be called only from the CPU to |
| * whom the rdp belongs. |
| */ |
| static void |
| __rcu_process_callbacks(struct rcu_state *rsp) |
| { |
| unsigned long flags; |
| bool needwake; |
| struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); |
| |
| WARN_ON_ONCE(!rdp->beenonline); |
| |
| /* Update RCU state based on any recent quiescent states. */ |
| rcu_check_quiescent_state(rsp, rdp); |
| |
| /* Does this CPU require a not-yet-started grace period? */ |
| local_irq_save(flags); |
| if (cpu_needs_another_gp(rsp, rdp)) { |
| raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */ |
| needwake = rcu_start_gp(rsp); |
| raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags); |
| if (needwake) |
| rcu_gp_kthread_wake(rsp); |
| } else { |
| local_irq_restore(flags); |
| } |
| |
| /* If there are callbacks ready, invoke them. */ |
| if (rcu_segcblist_ready_cbs(&rdp->cblist)) |
| invoke_rcu_callbacks(rsp, rdp); |
| |
| /* Do any needed deferred wakeups of rcuo kthreads. */ |
| do_nocb_deferred_wakeup(rdp); |
| } |
| |
| /* |
| * Do RCU core processing for the current CPU. |
| */ |
| static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) |
| { |
| struct rcu_state *rsp; |
| |
| if (cpu_is_offline(smp_processor_id())) |
| return; |
| trace_rcu_utilization(TPS("Start RCU core")); |
| for_each_rcu_flavor(rsp) |
| __rcu_process_callbacks(rsp); |
| trace_rcu_utilization(TPS("End RCU core")); |
| } |
| |
| /* |
| * Schedule RCU callback invocation. If the specified type of RCU |
| * does not support RCU priority boosting, just do a direct call, |
| * otherwise wake up the per-CPU kernel kthread. Note that because we |
| * are running on the current CPU with softirqs disabled, the |
| * rcu_cpu_kthread_task cannot disappear out from under us. |
| */ |
| static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) |
| { |
| if (unlikely(!READ_ONCE(rcu_scheduler_fully_active))) |
| return; |
| if (likely(!rsp->boost)) { |
| rcu_do_batch(rsp, rdp); |
| return; |
| } |
| invoke_rcu_callbacks_kthread(); |
| } |
| |
| static void invoke_rcu_core(void) |
| { |
| if (cpu_online(smp_processor_id())) |
| raise_softirq(RCU_SOFTIRQ); |
| } |
| |
| /* |
| * Handle any core-RCU processing required by a call_rcu() invocation. |
| */ |
| static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, |
| struct rcu_head *head, unsigned long flags) |
| { |
| bool needwake; |
| |
| /* |
| * If called from an extended quiescent state, invoke the RCU |
| * core in order to force a re-evaluation of RCU's idleness. |
| */ |
| if (!rcu_is_watching()) |
| invoke_rcu_core(); |
| |
| /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ |
| if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) |
| return; |
| |
| /* |
| * Force the grace period if too many callbacks or too long waiting. |
| * Enforce hysteresis, and don't invoke force_quiescent_state() |
| * if some other CPU has recently done so. Also, don't bother |
| * invoking force_quiescent_state() if the newly enqueued callback |
| * is the only one waiting for a grace period to complete. |
| */ |
| if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) > |
| rdp->qlen_last_fqs_check + qhimark)) { |
| |
| /* Are we ignoring a completed grace period? */ |
| note_gp_changes(rsp, rdp); |
| |
| /* Start a new grace period if one not already started. */ |
| if (!rcu_gp_in_progress(rsp)) { |
| struct rcu_node *rnp_root = rcu_get_root(rsp); |
| |
| raw_spin_lock_rcu_node(rnp_root); |
| needwake = rcu_start_gp(rsp); |
| raw_spin_unlock_rcu_node(rnp_root); |
| if (needwake) |
| rcu_gp_kthread_wake(rsp); |
| } else { |
| /* Give the grace period a kick. */ |
| rdp->blimit = LONG_MAX; |
| if (rsp->n_force_qs == rdp->n_force_qs_snap && |
| rcu_segcblist_first_pend_cb(&rdp->cblist) != head) |
| force_quiescent_state(rsp); |
| rdp->n_force_qs_snap = rsp->n_force_qs; |
| rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); |
| } |
| } |
| } |
| |
| /* |
| * RCU callback function to leak a callback. |
| */ |
| static void rcu_leak_callback(struct rcu_head *rhp) |
| { |
| } |
| |
| /* |
| * Helper function for call_rcu() and friends. The cpu argument will |
| * normally be -1, indicating "currently running CPU". It may specify |
| * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier() |
| * is expected to specify a CPU. |
| */ |
| static void |
| __call_rcu(struct rcu_head *head, rcu_callback_t func, |
| struct rcu_state *rsp, int cpu, bool lazy) |
| { |
| unsigned long flags; |
| struct rcu_data *rdp; |
| |
| /* Misaligned rcu_head! */ |
| WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1)); |
| |
| if (debug_rcu_head_queue(head)) { |
| /* |
| * Probable double call_rcu(), so leak the callback. |
| * Use rcu:rcu_callback trace event to find the previous |
| * time callback was passed to __call_rcu(). |
| */ |
| WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pF()!!!\n", |
| head, head->func); |
| WRITE_ONCE(head->func, rcu_leak_callback); |
| return; |
| } |
| head->func = func; |
| head->next = NULL; |
| local_irq_save(flags); |
| rdp = this_cpu_ptr(rsp->rda); |
| |
| /* Add the callback to our list. */ |
| if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) { |
| int offline; |
| |
| if (cpu != -1) |
| rdp = per_cpu_ptr(rsp->rda, cpu); |
| if (likely(rdp->mynode)) { |
| /* Post-boot, so this should be for a no-CBs CPU. */ |
| offline = !__call_rcu_nocb(rdp, head, lazy, flags); |
| WARN_ON_ONCE(offline); |
| /* Offline CPU, _call_rcu() illegal, leak callback. */ |
| local_irq_restore(flags); |
| return; |
| } |
| /* |
| * Very early boot, before rcu_init(). Initialize if needed |
| * and then drop through to queue the callback. |
| */ |
| BUG_ON(cpu != -1); |
| WARN_ON_ONCE(!rcu_is_watching()); |
| if (rcu_segcblist_empty(&rdp->cblist)) |
| rcu_segcblist_init(&rdp->cblist); |
| } |
| rcu_segcblist_enqueue(&rdp->cblist, head, lazy); |
| if (!lazy) |
| rcu_idle_count_callbacks_posted(); |
| |
| if (__is_kfree_rcu_offset((unsigned long)func)) |
| trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func, |
| rcu_segcblist_n_lazy_cbs(&rdp->cblist), |
| rcu_segcblist_n_cbs(&rdp->cblist)); |
| else |
| trace_rcu_callback(rsp->name, head, |
| rcu_segcblist_n_lazy_cbs(&rdp->cblist), |
| rcu_segcblist_n_cbs(&rdp->cblist)); |
| |
| /* Go handle any RCU core processing required. */ |
| __call_rcu_core(rsp, rdp, head, flags); |
| local_irq_restore(flags); |
| } |
| |
| /** |
| * call_rcu_sched() - Queue an RCU for invocation after sched grace period. |
| * @head: structure to be used for queueing the RCU updates. |
| * @func: actual callback function to be invoked after the grace period |
| * |
| * The callback function will be invoked some time after a full grace |
| * period elapses, in other words after all currently executing RCU |
| * read-side critical sections have completed. call_rcu_sched() assumes |
| * that the read-side critical sections end on enabling of preemption |
| * or on voluntary preemption. |
| * RCU read-side critical sections are delimited by : |
| * - rcu_read_lock_sched() and rcu_read_unlock_sched(), OR |
| * - anything that disables preemption. |
| * |
| * These may be nested. |
| * |
| * See the description of call_rcu() for more detailed information on |
| * memory ordering guarantees. |
| */ |
| void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) |
| { |
| __call_rcu(head, func, &rcu_sched_state, -1, 0); |
| } |
| EXPORT_SYMBOL_GPL(call_rcu_sched); |
| |
| /** |
| * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. |
| * @head: structure to be used for queueing the RCU updates. |
| * @func: actual callback function to be invoked after the grace period |
| * |
| * The callback function will be invoked some time after a full grace |
| * period elapses, in other words after all currently executing RCU |
| * read-side critical sections have completed. call_rcu_bh() assumes |
| * that the read-side critical sections end on completion of a softirq |
| * handler. This means that read-side critical sections in process |
| * context must not be interrupted by softirqs. This interface is to be |
| * used when most of the read-side critical sections are in softirq context. |
| * RCU read-side critical sections are delimited by : |
| * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
| * OR |
| * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
| * These may be nested. |
| * |
| * See the description of call_rcu() for more detailed information on |
| * memory ordering guarantees. |
| */ |
| void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) |
| { |
| __call_rcu(head, func, &rcu_bh_state, -1, 0); |
| } |
| EXPORT_SYMBOL_GPL(call_rcu_bh); |
| |
| /* |
| * Queue an RCU callback for lazy invocation after a grace period. |
| * This will likely be later named something like "call_rcu_lazy()", |
| * but this change will require some way of tagging the lazy RCU |
| * callbacks in the list of pending callbacks. Until then, this |
| * function may only be called from __kfree_rcu(). |
| */ |
| void kfree_call_rcu(struct rcu_head *head, |
| rcu_callback_t func) |
| { |
| __call_rcu(head, func, rcu_state_p, -1, 1); |
| } |
| EXPORT_SYMBOL_GPL(kfree_call_rcu); |
| |
| /* |
| * Because a context switch is a grace period for RCU-sched and RCU-bh, |
| * any blocking grace-period wait automatically implies a grace period |
| * if there is only one CPU online at any point time during execution |
| * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to |
| * occasionally incorrectly indicate that there are multiple CPUs online |
| * when there was in fact only one the whole time, as this just adds |
| * some overhead: RCU still operates correctly. |
| */ |
| static inline int rcu_blocking_is_gp(void) |
| { |
| int ret; |
| |
| might_sleep(); /* Check for RCU read-side critical section. */ |
| preempt_disable(); |
| ret = num_online_cpus() <= 1; |
| preempt_enable(); |
| return ret; |
| } |
| |
| /** |
| * synchronize_sched - wait until an rcu-sched grace period has elapsed. |
| * |
| * Control will return to the caller some time after a full rcu-sched |
| * grace period has elapsed, in other words after all currently executing |
| * rcu-sched read-side critical sections have completed. These read-side |
| * critical sections are delimited by rcu_read_lock_sched() and |
| * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(), |
| * local_irq_disable(), and so on may be used in place of |
| * rcu_read_lock_sched(). |
| * |
| * This means that all preempt_disable code sequences, including NMI and |
| * non-threaded hardware-interrupt handlers, in progress on entry will |
| * have completed before this primitive returns. However, this does not |
| * guarantee that softirq handlers will have completed, since in some |
| * kernels, these handlers can run in process context, and can block. |
| * |
| * Note that this guarantee implies further memory-ordering guarantees. |
| * On systems with more than one CPU, when synchronize_sched() returns, |
| * each CPU is guaranteed to have executed a full memory barrier since the |
| * end of its last RCU-sched read-side critical section whose beginning |
| * preceded the call to synchronize_sched(). In addition, each CPU having |
| * an RCU read-side critical section that extends beyond the return from |
| * synchronize_sched() is guaranteed to have executed a full memory barrier |
| * after the beginning of synchronize_sched() and before the beginning of |
| * that RCU read-side critical section. Note that these guarantees include |
| * CPUs that are offline, idle, or executing in user mode, as well as CPUs |
| * that are executing in the kernel. |
| * |
| * Furthermore, if CPU A invoked synchronize_sched(), which returned |
| * to its caller on CPU B, then both CPU A and CPU B are guaranteed |
| * to have executed a full memory barrier during the execution of |
| * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but |
| * again only if the system has more than one CPU). |
| */ |
| void synchronize_sched(void) |
| { |
| RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
| lock_is_held(&rcu_lock_map) || |
| lock_is_held(&rcu_sched_lock_map), |
| "Illegal synchronize_sched() in RCU-sched read-side critical section"); |
| if (rcu_blocking_is_gp()) |
| return; |
| if (rcu_gp_is_expedited()) |
| synchronize_sched_expedited(); |
| else |
| wait_rcu_gp(call_rcu_sched); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_sched); |
| |
| /** |
| * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. |
| * |
| * Control will return to the caller some time after a full rcu_bh grace |
| * period has elapsed, in other words after all currently executing rcu_bh |
| * read-side critical sections have completed. RCU read-side critical |
| * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(), |
| * and may be nested. |
| * |
| * See the description of synchronize_sched() for more detailed information |
| * on memory ordering guarantees. |
| */ |
| void synchronize_rcu_bh(void) |
| { |
| RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
| lock_is_held(&rcu_lock_map) || |
| lock_is_held(&rcu_sched_lock_map), |
| "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section"); |
| if (rcu_blocking_is_gp()) |
| return; |
| if (rcu_gp_is_expedited()) |
| synchronize_rcu_bh_expedited(); |
| else |
| wait_rcu_gp(call_rcu_bh); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_rcu_bh); |
| |
| /** |
| * get_state_synchronize_rcu - Snapshot current RCU state |
| * |
| * Returns a cookie that is used by a later call to cond_synchronize_rcu() |
| * to determine whether or not a full grace period has elapsed in the |
| * meantime. |
| */ |
| unsigned long get_state_synchronize_rcu(void) |
| { |
| /* |
| * Any prior manipulation of RCU-protected data must happen |
| * before the load from ->gpnum. |
| */ |
| smp_mb(); /* ^^^ */ |
| |
| /* |
| * Make sure this load happens before the purportedly |
| * time-consuming work between get_state_synchronize_rcu() |
| * and cond_synchronize_rcu(). |
| */ |
| return smp_load_acquire(&rcu_state_p->gpnum); |
| } |
| EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); |
| |
| /** |
| * cond_synchronize_rcu - Conditionally wait for an RCU grace period |
| * |
| * @oldstate: return value from earlier call to get_state_synchronize_rcu() |
| * |
| * If a full RCU grace period has elapsed since the earlier call to |
| * get_state_synchronize_rcu(), just return. Otherwise, invoke |
| * synchronize_rcu() to wait for a full grace period. |
| * |
| * Yes, this function does not take counter wrap into account. But |
| * counter wrap is harmless. If the counter wraps, we have waited for |
| * more than 2 billion grace periods (and way more on a 64-bit system!), |
| * so waiting for one additional grace period should be just fine. |
| */ |
| void cond_synchronize_rcu(unsigned long oldstate) |
| { |
| unsigned long newstate; |
| |
| /* |
| * Ensure that this load happens before any RCU-destructive |
| * actions the caller might carry out after we return. |
| */ |
| newstate = smp_load_acquire(&rcu_state_p->completed); |
| if (ULONG_CMP_GE(oldstate, newstate)) |
| synchronize_rcu(); |
| } |
| EXPORT_SYMBOL_GPL(cond_synchronize_rcu); |
| |
| /** |
| * get_state_synchronize_sched - Snapshot current RCU-sched state |
| * |
| * Returns a cookie that is used by a later call to cond_synchronize_sched() |
| * to determine whether or not a full grace period has elapsed in the |
| * meantime. |
| */ |
| unsigned long get_state_synchronize_sched(void) |
| { |
| /* |
| * Any prior manipulation of RCU-protected data must happen |
| * before the load from ->gpnum. |
| */ |
| smp_mb(); /* ^^^ */ |
| |
| /* |
| * Make sure this load happens before the purportedly |
| * time-consuming work between get_state_synchronize_sched() |
| * and cond_synchronize_sched(). |
| */ |
| return smp_load_acquire(&rcu_sched_state.gpnum); |
| } |
| EXPORT_SYMBOL_GPL(get_state_synchronize_sched); |
| <