| /* |
| * Read-Copy Update mechanism for mutual exclusion (tree-based version) |
| * Internal non-public definitions that provide either classic |
| * or preemptible semantics. |
| * |
| * 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, write to the Free Software |
| * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| * |
| * Copyright Red Hat, 2009 |
| * Copyright IBM Corporation, 2009 |
| * |
| * Author: Ingo Molnar <mingo@elte.hu> |
| * Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| */ |
| |
| #include <linux/delay.h> |
| #include <linux/gfp.h> |
| #include <linux/oom.h> |
| #include <linux/smpboot.h> |
| #include <linux/tick.h> |
| |
| #define RCU_KTHREAD_PRIO 1 |
| |
| #ifdef CONFIG_RCU_BOOST |
| #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO |
| #else |
| #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO |
| #endif |
| |
| #ifdef CONFIG_RCU_NOCB_CPU |
| static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ |
| static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ |
| static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
| static char __initdata nocb_buf[NR_CPUS * 5]; |
| #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ |
| |
| /* |
| * Check the RCU kernel configuration parameters and print informative |
| * messages about anything out of the ordinary. If you like #ifdef, you |
| * will love this function. |
| */ |
| static void __init rcu_bootup_announce_oddness(void) |
| { |
| #ifdef CONFIG_RCU_TRACE |
| printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); |
| #endif |
| #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) |
| printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
| CONFIG_RCU_FANOUT); |
| #endif |
| #ifdef CONFIG_RCU_FANOUT_EXACT |
| printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); |
| #endif |
| #ifdef CONFIG_RCU_FAST_NO_HZ |
| printk(KERN_INFO |
| "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); |
| #endif |
| #ifdef CONFIG_PROVE_RCU |
| printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); |
| #endif |
| #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE |
| printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); |
| #endif |
| #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
| printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n"); |
| #endif |
| #if defined(CONFIG_RCU_CPU_STALL_INFO) |
| printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n"); |
| #endif |
| #if NUM_RCU_LVL_4 != 0 |
| printk(KERN_INFO "\tFour-level hierarchy is enabled.\n"); |
| #endif |
| if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) |
| printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); |
| if (nr_cpu_ids != NR_CPUS) |
| printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); |
| #ifdef CONFIG_RCU_NOCB_CPU |
| #ifndef CONFIG_RCU_NOCB_CPU_NONE |
| if (!have_rcu_nocb_mask) { |
| zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL); |
| have_rcu_nocb_mask = true; |
| } |
| #ifdef CONFIG_RCU_NOCB_CPU_ZERO |
| pr_info("\tExperimental no-CBs CPU 0\n"); |
| cpumask_set_cpu(0, rcu_nocb_mask); |
| #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ |
| #ifdef CONFIG_RCU_NOCB_CPU_ALL |
| pr_info("\tExperimental no-CBs for all CPUs\n"); |
| cpumask_setall(rcu_nocb_mask); |
| #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ |
| #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ |
| if (have_rcu_nocb_mask) { |
| cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); |
| pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf); |
| if (rcu_nocb_poll) |
| pr_info("\tExperimental polled no-CBs CPUs.\n"); |
| } |
| #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ |
| } |
| |
| #ifdef CONFIG_TREE_PREEMPT_RCU |
| |
| struct rcu_state rcu_preempt_state = |
| RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); |
| DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); |
| static struct rcu_state *rcu_state = &rcu_preempt_state; |
| |
| static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
| |
| /* |
| * Tell them what RCU they are running. |
| */ |
| static void __init rcu_bootup_announce(void) |
| { |
| printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n"); |
| rcu_bootup_announce_oddness(); |
| } |
| |
| /* |
| * Return the number of RCU-preempt batches processed thus far |
| * for debug and statistics. |
| */ |
| long rcu_batches_completed_preempt(void) |
| { |
| return rcu_preempt_state.completed; |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); |
| |
| /* |
| * Return the number of RCU batches processed thus far for debug & stats. |
| */ |
| long rcu_batches_completed(void) |
| { |
| return rcu_batches_completed_preempt(); |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_completed); |
| |
| /* |
| * Force a quiescent state for preemptible RCU. |
| */ |
| void rcu_force_quiescent_state(void) |
| { |
| force_quiescent_state(&rcu_preempt_state); |
| } |
| EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
| |
| /* |
| * Record a preemptible-RCU quiescent state for the specified CPU. Note |
| * that this just means that the task currently running on the CPU is |
| * not in a quiescent state. There might be any number of tasks blocked |
| * while in an RCU read-side critical section. |
| * |
| * Unlike the other rcu_*_qs() functions, callers to this function |
| * must disable irqs in order to protect the assignment to |
| * ->rcu_read_unlock_special. |
| */ |
| static void rcu_preempt_qs(int cpu) |
| { |
| struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); |
| |
| if (rdp->passed_quiesce == 0) |
| trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); |
| rdp->passed_quiesce = 1; |
| current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
| } |
| |
| /* |
| * We have entered the scheduler, and the current task might soon be |
| * context-switched away from. If this task is in an RCU read-side |
| * critical section, we will no longer be able to rely on the CPU to |
| * record that fact, so we enqueue the task on the blkd_tasks list. |
| * The task will dequeue itself when it exits the outermost enclosing |
| * RCU read-side critical section. Therefore, the current grace period |
| * cannot be permitted to complete until the blkd_tasks list entries |
| * predating the current grace period drain, in other words, until |
| * rnp->gp_tasks becomes NULL. |
| * |
| * Caller must disable preemption. |
| */ |
| static void rcu_preempt_note_context_switch(int cpu) |
| { |
| struct task_struct *t = current; |
| unsigned long flags; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp; |
| |
| if (t->rcu_read_lock_nesting > 0 && |
| (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
| |
| /* Possibly blocking in an RCU read-side critical section. */ |
| rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
| rnp = rdp->mynode; |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
| t->rcu_blocked_node = rnp; |
| |
| /* |
| * If this CPU has already checked in, then this task |
| * will hold up the next grace period rather than the |
| * current grace period. Queue the task accordingly. |
| * If the task is queued for the current grace period |
| * (i.e., this CPU has not yet passed through a quiescent |
| * state for the current grace period), then as long |
| * as that task remains queued, the current grace period |
| * cannot end. Note that there is some uncertainty as |
| * to exactly when the current grace period started. |
| * We take a conservative approach, which can result |
| * in unnecessarily waiting on tasks that started very |
| * slightly after the current grace period began. C'est |
| * la vie!!! |
| * |
| * But first, note that the current CPU must still be |
| * on line! |
| */ |
| WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
| WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
| if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
| list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); |
| rnp->gp_tasks = &t->rcu_node_entry; |
| #ifdef CONFIG_RCU_BOOST |
| if (rnp->boost_tasks != NULL) |
| rnp->boost_tasks = rnp->gp_tasks; |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| } else { |
| list_add(&t->rcu_node_entry, &rnp->blkd_tasks); |
| if (rnp->qsmask & rdp->grpmask) |
| rnp->gp_tasks = &t->rcu_node_entry; |
| } |
| trace_rcu_preempt_task(rdp->rsp->name, |
| t->pid, |
| (rnp->qsmask & rdp->grpmask) |
| ? rnp->gpnum |
| : rnp->gpnum + 1); |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } else if (t->rcu_read_lock_nesting < 0 && |
| t->rcu_read_unlock_special) { |
| |
| /* |
| * Complete exit from RCU read-side critical section on |
| * behalf of preempted instance of __rcu_read_unlock(). |
| */ |
| rcu_read_unlock_special(t); |
| } |
| |
| /* |
| * Either we were not in an RCU read-side critical section to |
| * begin with, or we have now recorded that critical section |
| * globally. Either way, we can now note a quiescent state |
| * for this CPU. Again, if we were in an RCU read-side critical |
| * section, and if that critical section was blocking the current |
| * grace period, then the fact that the task has been enqueued |
| * means that we continue to block the current grace period. |
| */ |
| local_irq_save(flags); |
| rcu_preempt_qs(cpu); |
| local_irq_restore(flags); |
| } |
| |
| /* |
| * Check for preempted RCU readers blocking the current grace period |
| * for the specified rcu_node structure. If the caller needs a reliable |
| * answer, it must hold the rcu_node's ->lock. |
| */ |
| static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
| { |
| return rnp->gp_tasks != NULL; |
| } |
| |
| /* |
| * 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_node *rnp, unsigned long flags) |
| __releases(rnp->lock) |
| { |
| unsigned long mask; |
| struct rcu_node *rnp_p; |
| |
| if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| return; /* Still need more quiescent states! */ |
| } |
| |
| rnp_p = rnp->parent; |
| if (rnp_p == NULL) { |
| /* |
| * Either there is only one rcu_node in the tree, |
| * or tasks were kicked up to root rcu_node due to |
| * CPUs going offline. |
| */ |
| rcu_report_qs_rsp(&rcu_preempt_state, flags); |
| return; |
| } |
| |
| /* Report up the rest of the hierarchy. */ |
| mask = rnp->grpmask; |
| raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
| raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ |
| rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
| } |
| |
| /* |
| * Advance a ->blkd_tasks-list pointer to the next entry, instead |
| * returning NULL if at the end of the list. |
| */ |
| static struct list_head *rcu_next_node_entry(struct task_struct *t, |
| struct rcu_node *rnp) |
| { |
| struct list_head *np; |
| |
| np = t->rcu_node_entry.next; |
| if (np == &rnp->blkd_tasks) |
| np = NULL; |
| return np; |
| } |
| |
| /* |
| * Handle special cases during rcu_read_unlock(), such as needing to |
| * notify RCU core processing or task having blocked during the RCU |
| * read-side critical section. |
| */ |
| void rcu_read_unlock_special(struct task_struct *t) |
| { |
| int empty; |
| int empty_exp; |
| int empty_exp_now; |
| unsigned long flags; |
| struct list_head *np; |
| #ifdef CONFIG_RCU_BOOST |
| struct rt_mutex *rbmp = NULL; |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| struct rcu_node *rnp; |
| int special; |
| |
| /* NMI handlers cannot block and cannot safely manipulate state. */ |
| if (in_nmi()) |
| return; |
| |
| local_irq_save(flags); |
| |
| /* |
| * If RCU core is waiting for this CPU to exit critical section, |
| * let it know that we have done so. |
| */ |
| special = t->rcu_read_unlock_special; |
| if (special & RCU_READ_UNLOCK_NEED_QS) { |
| rcu_preempt_qs(smp_processor_id()); |
| } |
| |
| /* Hardware IRQ handlers cannot block. */ |
| if (in_irq() || in_serving_softirq()) { |
| local_irq_restore(flags); |
| return; |
| } |
| |
| /* Clean up if blocked during RCU read-side critical section. */ |
| if (special & RCU_READ_UNLOCK_BLOCKED) { |
| t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; |
| |
| /* |
| * Remove this task from the list it blocked on. The |
| * task can migrate while we acquire the lock, but at |
| * most one time. So at most two passes through loop. |
| */ |
| for (;;) { |
| rnp = t->rcu_blocked_node; |
| raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
| if (rnp == t->rcu_blocked_node) |
| break; |
| raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
| } |
| empty = !rcu_preempt_blocked_readers_cgp(rnp); |
| empty_exp = !rcu_preempted_readers_exp(rnp); |
| smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ |
| np = rcu_next_node_entry(t, rnp); |
| list_del_init(&t->rcu_node_entry); |
| t->rcu_blocked_node = NULL; |
| trace_rcu_unlock_preempted_task("rcu_preempt", |
| rnp->gpnum, t->pid); |
| if (&t->rcu_node_entry == rnp->gp_tasks) |
| rnp->gp_tasks = np; |
| if (&t->rcu_node_entry == rnp->exp_tasks) |
| rnp->exp_tasks = np; |
| #ifdef CONFIG_RCU_BOOST |
| if (&t->rcu_node_entry == rnp->boost_tasks) |
| rnp->boost_tasks = np; |
| /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ |
| if (t->rcu_boost_mutex) { |
| rbmp = t->rcu_boost_mutex; |
| t->rcu_boost_mutex = NULL; |
| } |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| |
| /* |
| * If this was the last task on the current list, and if |
| * we aren't waiting on any CPUs, report the quiescent state. |
| * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
| * so we must take a snapshot of the expedited state. |
| */ |
| empty_exp_now = !rcu_preempted_readers_exp(rnp); |
| if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { |
| trace_rcu_quiescent_state_report("preempt_rcu", |
| rnp->gpnum, |
| 0, rnp->qsmask, |
| rnp->level, |
| rnp->grplo, |
| rnp->grphi, |
| !!rnp->gp_tasks); |
| rcu_report_unblock_qs_rnp(rnp, flags); |
| } else { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| #ifdef CONFIG_RCU_BOOST |
| /* Unboost if we were boosted. */ |
| if (rbmp) |
| rt_mutex_unlock(rbmp); |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| |
| /* |
| * If this was the last task on the expedited lists, |
| * then we need to report up the rcu_node hierarchy. |
| */ |
| if (!empty_exp && empty_exp_now) |
| rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); |
| } else { |
| local_irq_restore(flags); |
| } |
| } |
| |
| #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
| |
| /* |
| * Dump detailed information for all tasks blocking the current RCU |
| * grace period on the specified rcu_node structure. |
| */ |
| static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) |
| { |
| unsigned long flags; |
| struct task_struct *t; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| return; |
| } |
| t = list_entry(rnp->gp_tasks, |
| struct task_struct, rcu_node_entry); |
| list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) |
| sched_show_task(t); |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| /* |
| * Dump detailed information for all tasks blocking the current RCU |
| * grace period. |
| */ |
| static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
| { |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| |
| rcu_print_detail_task_stall_rnp(rnp); |
| rcu_for_each_leaf_node(rsp, rnp) |
| rcu_print_detail_task_stall_rnp(rnp); |
| } |
| |
| #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ |
| |
| static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ |
| |
| #ifdef CONFIG_RCU_CPU_STALL_INFO |
| |
| static void rcu_print_task_stall_begin(struct rcu_node *rnp) |
| { |
| printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
| rnp->level, rnp->grplo, rnp->grphi); |
| } |
| |
| static void rcu_print_task_stall_end(void) |
| { |
| printk(KERN_CONT "\n"); |
| } |
| |
| #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ |
| |
| static void rcu_print_task_stall_begin(struct rcu_node *rnp) |
| { |
| } |
| |
| static void rcu_print_task_stall_end(void) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ |
| |
| /* |
| * Scan the current list of tasks blocked within RCU read-side critical |
| * sections, printing out the tid of each. |
| */ |
| static int rcu_print_task_stall(struct rcu_node *rnp) |
| { |
| struct task_struct *t; |
| int ndetected = 0; |
| |
| if (!rcu_preempt_blocked_readers_cgp(rnp)) |
| return 0; |
| rcu_print_task_stall_begin(rnp); |
| t = list_entry(rnp->gp_tasks, |
| struct task_struct, rcu_node_entry); |
| list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
| printk(KERN_CONT " P%d", t->pid); |
| ndetected++; |
| } |
| rcu_print_task_stall_end(); |
| return ndetected; |
| } |
| |
| /* |
| * Check that the list of blocked tasks for the newly completed grace |
| * period is in fact empty. It is a serious bug to complete a grace |
| * period that still has RCU readers blocked! This function must be |
| * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock |
| * must be held by the caller. |
| * |
| * Also, if there are blocked tasks on the list, they automatically |
| * block the newly created grace period, so set up ->gp_tasks accordingly. |
| */ |
| static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
| { |
| WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
| if (!list_empty(&rnp->blkd_tasks)) |
| rnp->gp_tasks = rnp->blkd_tasks.next; |
| WARN_ON_ONCE(rnp->qsmask); |
| } |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| |
| /* |
| * Handle tasklist migration for case in which all CPUs covered by the |
| * specified rcu_node have gone offline. Move them up to the root |
| * rcu_node. The reason for not just moving them to the immediate |
| * parent is to remove the need for rcu_read_unlock_special() to |
| * make more than two attempts to acquire the target rcu_node's lock. |
| * Returns true if there were tasks blocking the current RCU grace |
| * period. |
| * |
| * Returns 1 if there was previously a task blocking the current grace |
| * period on the specified rcu_node structure. |
| * |
| * The caller must hold rnp->lock with irqs disabled. |
| */ |
| static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
| struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| struct list_head *lp; |
| struct list_head *lp_root; |
| int retval = 0; |
| struct rcu_node *rnp_root = rcu_get_root(rsp); |
| struct task_struct *t; |
| |
| if (rnp == rnp_root) { |
| WARN_ONCE(1, "Last CPU thought to be offlined?"); |
| return 0; /* Shouldn't happen: at least one CPU online. */ |
| } |
| |
| /* If we are on an internal node, complain bitterly. */ |
| WARN_ON_ONCE(rnp != rdp->mynode); |
| |
| /* |
| * Move tasks up to root rcu_node. Don't try to get fancy for |
| * this corner-case operation -- just put this node's tasks |
| * at the head of the root node's list, and update the root node's |
| * ->gp_tasks and ->exp_tasks pointers to those of this node's, |
| * if non-NULL. This might result in waiting for more tasks than |
| * absolutely necessary, but this is a good performance/complexity |
| * tradeoff. |
| */ |
| if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) |
| retval |= RCU_OFL_TASKS_NORM_GP; |
| if (rcu_preempted_readers_exp(rnp)) |
| retval |= RCU_OFL_TASKS_EXP_GP; |
| lp = &rnp->blkd_tasks; |
| lp_root = &rnp_root->blkd_tasks; |
| while (!list_empty(lp)) { |
| t = list_entry(lp->next, typeof(*t), rcu_node_entry); |
| raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
| list_del(&t->rcu_node_entry); |
| t->rcu_blocked_node = rnp_root; |
| list_add(&t->rcu_node_entry, lp_root); |
| if (&t->rcu_node_entry == rnp->gp_tasks) |
| rnp_root->gp_tasks = rnp->gp_tasks; |
| if (&t->rcu_node_entry == rnp->exp_tasks) |
| rnp_root->exp_tasks = rnp->exp_tasks; |
| #ifdef CONFIG_RCU_BOOST |
| if (&t->rcu_node_entry == rnp->boost_tasks) |
| rnp_root->boost_tasks = rnp->boost_tasks; |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
| } |
| |
| rnp->gp_tasks = NULL; |
| rnp->exp_tasks = NULL; |
| #ifdef CONFIG_RCU_BOOST |
| rnp->boost_tasks = NULL; |
| /* |
| * In case root is being boosted and leaf was not. Make sure |
| * that we boost the tasks blocking the current grace period |
| * in this case. |
| */ |
| raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
| if (rnp_root->boost_tasks != NULL && |
| rnp_root->boost_tasks != rnp_root->gp_tasks && |
| rnp_root->boost_tasks != rnp_root->exp_tasks) |
| rnp_root->boost_tasks = rnp_root->gp_tasks; |
| raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| |
| return retval; |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| /* |
| * Check for a quiescent state from the current CPU. When a task blocks, |
| * the task is recorded in the corresponding CPU's rcu_node structure, |
| * which is checked elsewhere. |
| * |
| * Caller must disable hard irqs. |
| */ |
| static void rcu_preempt_check_callbacks(int cpu) |
| { |
| struct task_struct *t = current; |
| |
| if (t->rcu_read_lock_nesting == 0) { |
| rcu_preempt_qs(cpu); |
| return; |
| } |
| if (t->rcu_read_lock_nesting > 0 && |
| per_cpu(rcu_preempt_data, cpu).qs_pending) |
| t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
| } |
| |
| #ifdef CONFIG_RCU_BOOST |
| |
| static void rcu_preempt_do_callbacks(void) |
| { |
| rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); |
| } |
| |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| |
| /* |
| * Queue a preemptible-RCU callback for invocation after a grace period. |
| */ |
| void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
| { |
| __call_rcu(head, func, &rcu_preempt_state, -1, 0); |
| } |
| EXPORT_SYMBOL_GPL(call_rcu); |
| |
| /* |
| * 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, |
| void (*func)(struct rcu_head *rcu)) |
| { |
| __call_rcu(head, func, &rcu_preempt_state, -1, 1); |
| } |
| EXPORT_SYMBOL_GPL(kfree_call_rcu); |
| |
| /** |
| * synchronize_rcu - wait until a grace period has elapsed. |
| * |
| * Control will return to the caller some time after a full grace |
| * period has elapsed, in other words after all currently executing RCU |
| * read-side critical sections have completed. Note, however, that |
| * upon return from synchronize_rcu(), the caller might well be executing |
| * concurrently with new RCU read-side critical sections that began while |
| * synchronize_rcu() was waiting. RCU read-side critical sections are |
| * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. |
| * |
| * See the description of synchronize_sched() for more detailed information |
| * on memory ordering guarantees. |
| */ |
| void synchronize_rcu(void) |
| { |
| rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
| !lock_is_held(&rcu_lock_map) && |
| !lock_is_held(&rcu_sched_lock_map), |
| "Illegal synchronize_rcu() in RCU read-side critical section"); |
| if (!rcu_scheduler_active) |
| return; |
| if (rcu_expedited) |
| synchronize_rcu_expedited(); |
| else |
| wait_rcu_gp(call_rcu); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_rcu); |
| |
| static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
| static unsigned long sync_rcu_preempt_exp_count; |
| static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
| |
| /* |
| * Return non-zero if there are any tasks in RCU read-side critical |
| * sections blocking the current preemptible-RCU expedited grace period. |
| * If there is no preemptible-RCU expedited grace period currently in |
| * progress, returns zero unconditionally. |
| */ |
| static int rcu_preempted_readers_exp(struct rcu_node *rnp) |
| { |
| return rnp->exp_tasks != NULL; |
| } |
| |
| /* |
| * return non-zero if there is no RCU expedited grace period in progress |
| * for the specified rcu_node structure, in other words, if all CPUs and |
| * tasks covered by the specified rcu_node structure have done their bit |
| * for the current expedited grace period. Works only for preemptible |
| * RCU -- other RCU implementation use other means. |
| * |
| * Caller must hold sync_rcu_preempt_exp_mutex. |
| */ |
| static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) |
| { |
| return !rcu_preempted_readers_exp(rnp) && |
| ACCESS_ONCE(rnp->expmask) == 0; |
| } |
| |
| /* |
| * Report the exit from RCU read-side critical section for the last task |
| * that queued itself during or before the current expedited preemptible-RCU |
| * grace period. This event is reported either to the rcu_node structure on |
| * which the task was queued or to one of that rcu_node structure's ancestors, |
| * recursively up the tree. (Calm down, calm down, we do the recursion |
| * iteratively!) |
| * |
| * Most callers will set the "wake" flag, but the task initiating the |
| * expedited grace period need not wake itself. |
| * |
| * Caller must hold sync_rcu_preempt_exp_mutex. |
| */ |
| static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
| bool wake) |
| { |
| unsigned long flags; |
| unsigned long mask; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| for (;;) { |
| if (!sync_rcu_preempt_exp_done(rnp)) { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| break; |
| } |
| if (rnp->parent == NULL) { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| if (wake) |
| wake_up(&sync_rcu_preempt_exp_wq); |
| break; |
| } |
| mask = rnp->grpmask; |
| raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
| rnp = rnp->parent; |
| raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
| rnp->expmask &= ~mask; |
| } |
| } |
| |
| /* |
| * Snapshot the tasks blocking the newly started preemptible-RCU expedited |
| * grace period for the specified rcu_node structure. If there are no such |
| * tasks, report it up the rcu_node hierarchy. |
| * |
| * Caller must hold sync_rcu_preempt_exp_mutex and must exclude |
| * CPU hotplug operations. |
| */ |
| static void |
| sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) |
| { |
| unsigned long flags; |
| int must_wait = 0; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| if (list_empty(&rnp->blkd_tasks)) { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } else { |
| rnp->exp_tasks = rnp->blkd_tasks.next; |
| rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
| must_wait = 1; |
| } |
| if (!must_wait) |
| rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ |
| } |
| |
| /** |
| * synchronize_rcu_expedited - Brute-force RCU grace period |
| * |
| * Wait for an RCU-preempt grace period, but expedite it. The basic |
| * idea is to invoke synchronize_sched_expedited() to push all the tasks to |
| * the ->blkd_tasks lists and wait for this list to drain. This consumes |
| * significant time on all CPUs and is unfriendly to real-time workloads, |
| * so is thus not recommended for any sort of common-case code. |
| * In fact, if you are using synchronize_rcu_expedited() in a loop, |
| * please restructure your code to batch your updates, and then Use a |
| * single synchronize_rcu() instead. |
| * |
| * Note that it is illegal to call this function while holding any lock |
| * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal |
| * to call this function from a CPU-hotplug notifier. Failing to observe |
| * these restriction will result in deadlock. |
| */ |
| void synchronize_rcu_expedited(void) |
| { |
| unsigned long flags; |
| struct rcu_node *rnp; |
| struct rcu_state *rsp = &rcu_preempt_state; |
| unsigned long snap; |
| int trycount = 0; |
| |
| smp_mb(); /* Caller's modifications seen first by other CPUs. */ |
| snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; |
| smp_mb(); /* Above access cannot bleed into critical section. */ |
| |
| /* |
| * Block CPU-hotplug operations. This means that any CPU-hotplug |
| * operation that finds an rcu_node structure with tasks in the |
| * process of being boosted will know that all tasks blocking |
| * this expedited grace period will already be in the process of |
| * being boosted. This simplifies the process of moving tasks |
| * from leaf to root rcu_node structures. |
| */ |
| get_online_cpus(); |
| |
| /* |
| * Acquire lock, falling back to synchronize_rcu() if too many |
| * lock-acquisition failures. Of course, if someone does the |
| * expedited grace period for us, just leave. |
| */ |
| while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { |
| if (ULONG_CMP_LT(snap, |
| ACCESS_ONCE(sync_rcu_preempt_exp_count))) { |
| put_online_cpus(); |
| goto mb_ret; /* Others did our work for us. */ |
| } |
| if (trycount++ < 10) { |
| udelay(trycount * num_online_cpus()); |
| } else { |
| put_online_cpus(); |
| wait_rcu_gp(call_rcu); |
| return; |
| } |
| } |
| if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { |
| put_online_cpus(); |
| goto unlock_mb_ret; /* Others did our work for us. */ |
| } |
| |
| /* force all RCU readers onto ->blkd_tasks lists. */ |
| synchronize_sched_expedited(); |
| |
| /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
| rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| rnp->expmask = rnp->qsmaskinit; |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| /* Snapshot current state of ->blkd_tasks lists. */ |
| rcu_for_each_leaf_node(rsp, rnp) |
| sync_rcu_preempt_exp_init(rsp, rnp); |
| if (NUM_RCU_NODES > 1) |
| sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); |
| |
| put_online_cpus(); |
| |
| /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
| rnp = rcu_get_root(rsp); |
| wait_event(sync_rcu_preempt_exp_wq, |
| sync_rcu_preempt_exp_done(rnp)); |
| |
| /* Clean up and exit. */ |
| smp_mb(); /* ensure expedited GP seen before counter increment. */ |
| ACCESS_ONCE(sync_rcu_preempt_exp_count)++; |
| unlock_mb_ret: |
| mutex_unlock(&sync_rcu_preempt_exp_mutex); |
| mb_ret: |
| smp_mb(); /* ensure subsequent action seen after grace period. */ |
| } |
| EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
| |
| /** |
| * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. |
| * |
| * Note that this primitive does not necessarily wait for an RCU grace period |
| * to complete. For example, if there are no RCU callbacks queued anywhere |
| * in the system, then rcu_barrier() is within its rights to return |
| * immediately, without waiting for anything, much less an RCU grace period. |
| */ |
| void rcu_barrier(void) |
| { |
| _rcu_barrier(&rcu_preempt_state); |
| } |
| EXPORT_SYMBOL_GPL(rcu_barrier); |
| |
| /* |
| * Initialize preemptible RCU's state structures. |
| */ |
| static void __init __rcu_init_preempt(void) |
| { |
| rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
| } |
| |
| #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
| |
| static struct rcu_state *rcu_state = &rcu_sched_state; |
| |
| /* |
| * Tell them what RCU they are running. |
| */ |
| static void __init rcu_bootup_announce(void) |
| { |
| printk(KERN_INFO "Hierarchical RCU implementation.\n"); |
| rcu_bootup_announce_oddness(); |
| } |
| |
| /* |
| * Return the number of RCU batches processed thus far for debug & stats. |
| */ |
| long rcu_batches_completed(void) |
| { |
| return rcu_batches_completed_sched(); |
| } |
| EXPORT_SYMBOL_GPL(rcu_batches_completed); |
| |
| /* |
| * Force a quiescent state for RCU, which, because there is no preemptible |
| * RCU, becomes the same as rcu-sched. |
| */ |
| void rcu_force_quiescent_state(void) |
| { |
| rcu_sched_force_quiescent_state(); |
| } |
| EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
| |
| /* |
| * Because preemptible RCU does not exist, we never have to check for |
| * CPUs being in quiescent states. |
| */ |
| static void rcu_preempt_note_context_switch(int cpu) |
| { |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, there are never any preempted |
| * RCU readers. |
| */ |
| static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
| { |
| return 0; |
| } |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| |
| /* Because preemptible RCU does not exist, no quieting of tasks. */ |
| static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
| { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| /* |
| * Because preemptible RCU does not exist, we never have to check for |
| * tasks blocked within RCU read-side critical sections. |
| */ |
| static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
| { |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, we never have to check for |
| * tasks blocked within RCU read-side critical sections. |
| */ |
| static int rcu_print_task_stall(struct rcu_node *rnp) |
| { |
| return 0; |
| } |
| |
| /* |
| * Because there is no preemptible RCU, there can be no readers blocked, |
| * so there is no need to check for blocked tasks. So check only for |
| * bogus qsmask values. |
| */ |
| static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
| { |
| WARN_ON_ONCE(rnp->qsmask); |
| } |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| |
| /* |
| * Because preemptible RCU does not exist, it never needs to migrate |
| * tasks that were blocked within RCU read-side critical sections, and |
| * such non-existent tasks cannot possibly have been blocking the current |
| * grace period. |
| */ |
| static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
| struct rcu_node *rnp, |
| struct rcu_data *rdp) |
| { |
| return 0; |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| /* |
| * Because preemptible RCU does not exist, it never has any callbacks |
| * to check. |
| */ |
| static void rcu_preempt_check_callbacks(int cpu) |
| { |
| } |
| |
| /* |
| * 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(). |
| * |
| * Because there is no preemptible RCU, we use RCU-sched instead. |
| */ |
| void kfree_call_rcu(struct rcu_head *head, |
| void (*func)(struct rcu_head *rcu)) |
| { |
| __call_rcu(head, func, &rcu_sched_state, -1, 1); |
| } |
| EXPORT_SYMBOL_GPL(kfree_call_rcu); |
| |
| /* |
| * Wait for an rcu-preempt grace period, but make it happen quickly. |
| * But because preemptible RCU does not exist, map to rcu-sched. |
| */ |
| void synchronize_rcu_expedited(void) |
| { |
| synchronize_sched_expedited(); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| |
| /* |
| * Because preemptible RCU does not exist, there is never any need to |
| * report on tasks preempted in RCU read-side critical sections during |
| * expedited RCU grace periods. |
| */ |
| static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
| bool wake) |
| { |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| /* |
| * Because preemptible RCU does not exist, rcu_barrier() is just |
| * another name for rcu_barrier_sched(). |
| */ |
| void rcu_barrier(void) |
| { |
| rcu_barrier_sched(); |
| } |
| EXPORT_SYMBOL_GPL(rcu_barrier); |
| |
| /* |
| * Because preemptible RCU does not exist, it need not be initialized. |
| */ |
| static void __init __rcu_init_preempt(void) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
| |
| #ifdef CONFIG_RCU_BOOST |
| |
| #include "rtmutex_common.h" |
| |
| #ifdef CONFIG_RCU_TRACE |
| |
| static void rcu_initiate_boost_trace(struct rcu_node *rnp) |
| { |
| if (list_empty(&rnp->blkd_tasks)) |
| rnp->n_balk_blkd_tasks++; |
| else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) |
| rnp->n_balk_exp_gp_tasks++; |
| else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) |
| rnp->n_balk_boost_tasks++; |
| else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) |
| rnp->n_balk_notblocked++; |
| else if (rnp->gp_tasks != NULL && |
| ULONG_CMP_LT(jiffies, rnp->boost_time)) |
| rnp->n_balk_notyet++; |
| else |
| rnp->n_balk_nos++; |
| } |
| |
| #else /* #ifdef CONFIG_RCU_TRACE */ |
| |
| static void rcu_initiate_boost_trace(struct rcu_node *rnp) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_TRACE */ |
| |
| static void rcu_wake_cond(struct task_struct *t, int status) |
| { |
| /* |
| * If the thread is yielding, only wake it when this |
| * is invoked from idle |
| */ |
| if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) |
| wake_up_process(t); |
| } |
| |
| /* |
| * Carry out RCU priority boosting on the task indicated by ->exp_tasks |
| * or ->boost_tasks, advancing the pointer to the next task in the |
| * ->blkd_tasks list. |
| * |
| * Note that irqs must be enabled: boosting the task can block. |
| * Returns 1 if there are more tasks needing to be boosted. |
| */ |
| static int rcu_boost(struct rcu_node *rnp) |
| { |
| unsigned long flags; |
| struct rt_mutex mtx; |
| struct task_struct *t; |
| struct list_head *tb; |
| |
| if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) |
| return 0; /* Nothing left to boost. */ |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| |
| /* |
| * Recheck under the lock: all tasks in need of boosting |
| * might exit their RCU read-side critical sections on their own. |
| */ |
| if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| return 0; |
| } |
| |
| /* |
| * Preferentially boost tasks blocking expedited grace periods. |
| * This cannot starve the normal grace periods because a second |
| * expedited grace period must boost all blocked tasks, including |
| * those blocking the pre-existing normal grace period. |
| */ |
| if (rnp->exp_tasks != NULL) { |
| tb = rnp->exp_tasks; |
| rnp->n_exp_boosts++; |
| } else { |
| tb = rnp->boost_tasks; |
| rnp->n_normal_boosts++; |
| } |
| rnp->n_tasks_boosted++; |
| |
| /* |
| * We boost task t by manufacturing an rt_mutex that appears to |
| * be held by task t. We leave a pointer to that rt_mutex where |
| * task t can find it, and task t will release the mutex when it |
| * exits its outermost RCU read-side critical section. Then |
| * simply acquiring this artificial rt_mutex will boost task |
| * t's priority. (Thanks to tglx for suggesting this approach!) |
| * |
| * Note that task t must acquire rnp->lock to remove itself from |
| * the ->blkd_tasks list, which it will do from exit() if from |
| * nowhere else. We therefore are guaranteed that task t will |
| * stay around at least until we drop rnp->lock. Note that |
| * rnp->lock also resolves races between our priority boosting |
| * and task t's exiting its outermost RCU read-side critical |
| * section. |
| */ |
| t = container_of(tb, struct task_struct, rcu_node_entry); |
| rt_mutex_init_proxy_locked(&mtx, t); |
| t->rcu_boost_mutex = &mtx; |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ |
| rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ |
| |
| return ACCESS_ONCE(rnp->exp_tasks) != NULL || |
| ACCESS_ONCE(rnp->boost_tasks) != NULL; |
| } |
| |
| /* |
| * Priority-boosting kthread. One per leaf rcu_node and one for the |
| * root rcu_node. |
| */ |
| static int rcu_boost_kthread(void *arg) |
| { |
| struct rcu_node *rnp = (struct rcu_node *)arg; |
| int spincnt = 0; |
| int more2boost; |
| |
| trace_rcu_utilization("Start boost kthread@init"); |
| for (;;) { |
| rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
| trace_rcu_utilization("End boost kthread@rcu_wait"); |
| rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
| trace_rcu_utilization("Start boost kthread@rcu_wait"); |
| rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
| more2boost = rcu_boost(rnp); |
| if (more2boost) |
| spincnt++; |
| else |
| spincnt = 0; |
| if (spincnt > 10) { |
| rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
| trace_rcu_utilization("End boost kthread@rcu_yield"); |
| schedule_timeout_interruptible(2); |
| trace_rcu_utilization("Start boost kthread@rcu_yield"); |
| spincnt = 0; |
| } |
| } |
| /* NOTREACHED */ |
| trace_rcu_utilization("End boost kthread@notreached"); |
| return 0; |
| } |
| |
| /* |
| * Check to see if it is time to start boosting RCU readers that are |
| * blocking the current grace period, and, if so, tell the per-rcu_node |
| * kthread to start boosting them. If there is an expedited grace |
| * period in progress, it is always time to boost. |
| * |
| * The caller must hold rnp->lock, which this function releases. |
| * The ->boost_kthread_task is immortal, so we don't need to worry |
| * about it going away. |
| */ |
| static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
| { |
| struct task_struct *t; |
| |
| if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
| rnp->n_balk_exp_gp_tasks++; |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| return; |
| } |
| if (rnp->exp_tasks != NULL || |
| (rnp->gp_tasks != NULL && |
| rnp->boost_tasks == NULL && |
| rnp->qsmask == 0 && |
| ULONG_CMP_GE(jiffies, rnp->boost_time))) { |
| if (rnp->exp_tasks == NULL) |
| rnp->boost_tasks = rnp->gp_tasks; |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| t = rnp->boost_kthread_task; |
| if (t) |
| rcu_wake_cond(t, rnp->boost_kthread_status); |
| } else { |
| rcu_initiate_boost_trace(rnp); |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| } |
| |
| /* |
| * Wake up the per-CPU kthread to invoke RCU callbacks. |
| */ |
| static void invoke_rcu_callbacks_kthread(void) |
| { |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| __this_cpu_write(rcu_cpu_has_work, 1); |
| if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
| current != __this_cpu_read(rcu_cpu_kthread_task)) { |
| rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), |
| __this_cpu_read(rcu_cpu_kthread_status)); |
| } |
| local_irq_restore(flags); |
| } |
| |
| /* |
| * Is the current CPU running the RCU-callbacks kthread? |
| * Caller must have preemption disabled. |
| */ |
| static bool rcu_is_callbacks_kthread(void) |
| { |
| return __get_cpu_var(rcu_cpu_kthread_task) == current; |
| } |
| |
| #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
| |
| /* |
| * Do priority-boost accounting for the start of a new grace period. |
| */ |
| static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
| { |
| rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; |
| } |
| |
| /* |
| * Create an RCU-boost kthread for the specified node if one does not |
| * already exist. We only create this kthread for preemptible RCU. |
| * Returns zero if all is well, a negated errno otherwise. |
| */ |
| static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
| struct rcu_node *rnp) |
| { |
| int rnp_index = rnp - &rsp->node[0]; |
| unsigned long flags; |
| struct sched_param sp; |
| struct task_struct *t; |
| |
| if (&rcu_preempt_state != rsp) |
| return 0; |
| |
| if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) |
| return 0; |
| |
| rsp->boost = 1; |
| if (rnp->boost_kthread_task != NULL) |
| return 0; |
| t = kthread_create(rcu_boost_kthread, (void *)rnp, |
| "rcub/%d", rnp_index); |
| if (IS_ERR(t)) |
| return PTR_ERR(t); |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| rnp->boost_kthread_task = t; |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| sp.sched_priority = RCU_BOOST_PRIO; |
| sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
| wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
| return 0; |
| } |
| |
| static void rcu_kthread_do_work(void) |
| { |
| rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); |
| rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); |
| rcu_preempt_do_callbacks(); |
| } |
| |
| static void rcu_cpu_kthread_setup(unsigned int cpu) |
| { |
| struct sched_param sp; |
| |
| sp.sched_priority = RCU_KTHREAD_PRIO; |
| sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
| } |
| |
| static void rcu_cpu_kthread_park(unsigned int cpu) |
| { |
| per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
| } |
| |
| static int rcu_cpu_kthread_should_run(unsigned int cpu) |
| { |
| return __get_cpu_var(rcu_cpu_has_work); |
| } |
| |
| /* |
| * Per-CPU kernel thread that invokes RCU callbacks. This replaces the |
| * RCU softirq used in flavors and configurations of RCU that do not |
| * support RCU priority boosting. |
| */ |
| static void rcu_cpu_kthread(unsigned int cpu) |
| { |
| unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status); |
| char work, *workp = &__get_cpu_var(rcu_cpu_has_work); |
| int spincnt; |
| |
| for (spincnt = 0; spincnt < 10; spincnt++) { |
| trace_rcu_utilization("Start CPU kthread@rcu_wait"); |
| local_bh_disable(); |
| *statusp = RCU_KTHREAD_RUNNING; |
| this_cpu_inc(rcu_cpu_kthread_loops); |
| local_irq_disable(); |
| work = *workp; |
| *workp = 0; |
| local_irq_enable(); |
| if (work) |
| rcu_kthread_do_work(); |
| local_bh_enable(); |
| if (*workp == 0) { |
| trace_rcu_utilization("End CPU kthread@rcu_wait"); |
| *statusp = RCU_KTHREAD_WAITING; |
| return; |
| } |
| } |
| *statusp = RCU_KTHREAD_YIELDING; |
| trace_rcu_utilization("Start CPU kthread@rcu_yield"); |
| schedule_timeout_interruptible(2); |
| trace_rcu_utilization("End CPU kthread@rcu_yield"); |
| *statusp = RCU_KTHREAD_WAITING; |
| } |
| |
| /* |
| * Set the per-rcu_node kthread's affinity to cover all CPUs that are |
| * served by the rcu_node in question. The CPU hotplug lock is still |
| * held, so the value of rnp->qsmaskinit will be stable. |
| * |
| * We don't include outgoingcpu in the affinity set, use -1 if there is |
| * no outgoing CPU. If there are no CPUs left in the affinity set, |
| * this function allows the kthread to execute on any CPU. |
| */ |
| static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
| { |
| struct task_struct *t = rnp->boost_kthread_task; |
| unsigned long mask = rnp->qsmaskinit; |
| cpumask_var_t cm; |
| int cpu; |
| |
| if (!t) |
| return; |
| if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
| return; |
| for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
| if ((mask & 0x1) && cpu != outgoingcpu) |
| cpumask_set_cpu(cpu, cm); |
| if (cpumask_weight(cm) == 0) { |
| cpumask_setall(cm); |
| for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) |
| cpumask_clear_cpu(cpu, cm); |
| WARN_ON_ONCE(cpumask_weight(cm) == 0); |
| } |
| set_cpus_allowed_ptr(t, cm); |
| free_cpumask_var(cm); |
| } |
| |
| static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
| .store = &rcu_cpu_kthread_task, |
| .thread_should_run = rcu_cpu_kthread_should_run, |
| .thread_fn = rcu_cpu_kthread, |
| .thread_comm = "rcuc/%u", |
| .setup = rcu_cpu_kthread_setup, |
| .park = rcu_cpu_kthread_park, |
| }; |
| |
| /* |
| * Spawn all kthreads -- called as soon as the scheduler is running. |
| */ |
| static int __init rcu_spawn_kthreads(void) |
| { |
| struct rcu_node *rnp; |
| int cpu; |
| |
| rcu_scheduler_fully_active = 1; |
| for_each_possible_cpu(cpu) |
| per_cpu(rcu_cpu_has_work, cpu) = 0; |
| BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
| rnp = rcu_get_root(rcu_state); |
| (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
| if (NUM_RCU_NODES > 1) { |
| rcu_for_each_leaf_node(rcu_state, rnp) |
| (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
| } |
| return 0; |
| } |
| early_initcall(rcu_spawn_kthreads); |
| |
| static void __cpuinit rcu_prepare_kthreads(int cpu) |
| { |
| struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); |
| struct rcu_node *rnp = rdp->mynode; |
| |
| /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ |
| if (rcu_scheduler_fully_active) |
| (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); |
| } |
| |
| #else /* #ifdef CONFIG_RCU_BOOST */ |
| |
| static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
| { |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| static void invoke_rcu_callbacks_kthread(void) |
| { |
| WARN_ON_ONCE(1); |
| } |
| |
| static bool rcu_is_callbacks_kthread(void) |
| { |
| return false; |
| } |
| |
| static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
| { |
| } |
| |
| static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
| { |
| } |
| |
| static int __init rcu_scheduler_really_started(void) |
| { |
| rcu_scheduler_fully_active = 1; |
| return 0; |
| } |
| early_initcall(rcu_scheduler_really_started); |
| |
| static void __cpuinit rcu_prepare_kthreads(int cpu) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
| |
| #if !defined(CONFIG_RCU_FAST_NO_HZ) |
| |
| /* |
| * Check to see if any future RCU-related work will need to be done |
| * by the current CPU, even if none need be done immediately, returning |
| * 1 if so. This function is part of the RCU implementation; it is -not- |
| * an exported member of the RCU API. |
| * |
| * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
| * any flavor of RCU. |
| */ |
| int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) |
| { |
| *delta_jiffies = ULONG_MAX; |
| return rcu_cpu_has_callbacks(cpu, NULL); |
| } |
| |
| /* |
| * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up |
| * after it. |
| */ |
| static void rcu_cleanup_after_idle(int cpu) |
| { |
| } |
| |
| /* |
| * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
| * is nothing. |
| */ |
| static void rcu_prepare_for_idle(int cpu) |
| { |
| } |
| |
| /* |
| * Don't bother keeping a running count of the number of RCU callbacks |
| * posted because CONFIG_RCU_FAST_NO_HZ=n. |
| */ |
| static void rcu_idle_count_callbacks_posted(void) |
| { |
| } |
| |
| #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
| |
| /* |
| * This code is invoked when a CPU goes idle, at which point we want |
| * to have the CPU do everything required for RCU so that it can enter |
| * the energy-efficient dyntick-idle mode. This is handled by a |
| * state machine implemented by rcu_prepare_for_idle() below. |
| * |
| * The following three proprocessor symbols control this state machine: |
| * |
| * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted |
| * to sleep in dyntick-idle mode with RCU callbacks pending. This |
| * is sized to be roughly one RCU grace period. Those energy-efficiency |
| * benchmarkers who might otherwise be tempted to set this to a large |
| * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your |
| * system. And if you are -that- concerned about energy efficiency, |
| * just power the system down and be done with it! |
| * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
| * permitted to sleep in dyntick-idle mode with only lazy RCU |
| * callbacks pending. Setting this too high can OOM your system. |
| * |
| * The values below work well in practice. If future workloads require |
| * adjustment, they can be converted into kernel config parameters, though |
| * making the state machine smarter might be a better option. |
| */ |
| #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
| #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
| |
| static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; |
| module_param(rcu_idle_gp_delay, int, 0644); |
| static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; |
| module_param(rcu_idle_lazy_gp_delay, int, 0644); |
| |
| extern int tick_nohz_enabled; |
| |
| /* |
| * Try to advance callbacks for all flavors of RCU on the current CPU. |
| * Afterwards, if there are any callbacks ready for immediate invocation, |
| * return true. |
| */ |
| static bool rcu_try_advance_all_cbs(void) |
| { |
| bool cbs_ready = false; |
| struct rcu_data *rdp; |
| struct rcu_node *rnp; |
| struct rcu_state *rsp; |
| |
| for_each_rcu_flavor(rsp) { |
| rdp = this_cpu_ptr(rsp->rda); |
| rnp = rdp->mynode; |
| |
| /* |
| * Don't bother checking unless a grace period has |
| * completed since we last checked and there are |
| * callbacks not yet ready to invoke. |
| */ |
| if (rdp->completed != rnp->completed && |
| rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) |
| rcu_process_gp_end(rsp, rdp); |
| |
| if (cpu_has_callbacks_ready_to_invoke(rdp)) |
| cbs_ready = true; |
| } |
| return cbs_ready; |
| } |
| |
| /* |
| * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
| * to invoke. If the CPU has callbacks, try to advance them. Tell the |
| * caller to set the timeout based on whether or not there are non-lazy |
| * callbacks. |
| * |
| * The caller must have disabled interrupts. |
| */ |
| int rcu_needs_cpu(int cpu, unsigned long *dj) |
| { |
| struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
| |
| /* Snapshot to detect later posting of non-lazy callback. */ |
| rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; |
| |
| /* If no callbacks, RCU doesn't need the CPU. */ |
| if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) { |
| *dj = ULONG_MAX; |
| return 0; |
| } |
| |
| /* Attempt to advance callbacks. */ |
| if (rcu_try_advance_all_cbs()) { |
| /* Some ready to invoke, so initiate later invocation. */ |
| invoke_rcu_core(); |
| return 1; |
| } |
| rdtp->last_accelerate = jiffies; |
| |
| /* Request timer delay depending on laziness, and round. */ |
| if (!rdtp->all_lazy) { |
| *dj = round_up(rcu_idle_gp_delay + jiffies, |
| rcu_idle_gp_delay) - jiffies; |
| } else { |
| *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; |
| } |
| return 0; |
| } |
| |
| /* |
| * Prepare a CPU for idle from an RCU perspective. The first major task |
| * is to sense whether nohz mode has been enabled or disabled via sysfs. |
| * The second major task is to check to see if a non-lazy callback has |
| * arrived at a CPU that previously had only lazy callbacks. The third |
| * major task is to accelerate (that is, assign grace-period numbers to) |
| * any recently arrived callbacks. |
| * |
| * The caller must have disabled interrupts. |
| */ |
| static void rcu_prepare_for_idle(int cpu) |
| { |
| struct rcu_data *rdp; |
| struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
| struct rcu_node *rnp; |
| struct rcu_state *rsp; |
| int tne; |
| |
| /* Handle nohz enablement switches conservatively. */ |
| tne = ACCESS_ONCE(tick_nohz_enabled); |
| if (tne != rdtp->tick_nohz_enabled_snap) { |
| if (rcu_cpu_has_callbacks(cpu, NULL)) |
| invoke_rcu_core(); /* force nohz to see update. */ |
| rdtp->tick_nohz_enabled_snap = tne; |
| return; |
| } |
| if (!tne) |
| return; |
| |
| /* If this is a no-CBs CPU, no callbacks, just return. */ |
| if (rcu_is_nocb_cpu(cpu)) |
| return; |
| |
| /* |
| * If a non-lazy callback arrived at a CPU having only lazy |
| * callbacks, invoke RCU core for the side-effect of recalculating |
| * idle duration on re-entry to idle. |
| */ |
| if (rdtp->all_lazy && |
| rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { |
| invoke_rcu_core(); |
| return; |
| } |
| |
| /* |
| * If we have not yet accelerated this jiffy, accelerate all |
| * callbacks on this CPU. |
| */ |
| if (rdtp->last_accelerate == jiffies) |
| return; |
| rdtp->last_accelerate = jiffies; |
| for_each_rcu_flavor(rsp) { |
| rdp = per_cpu_ptr(rsp->rda, cpu); |
| if (!*rdp->nxttail[RCU_DONE_TAIL]) |
| continue; |
| rnp = rdp->mynode; |
| raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
| rcu_accelerate_cbs(rsp, rnp, rdp); |
| raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
| } |
| } |
| |
| /* |
| * Clean up for exit from idle. Attempt to advance callbacks based on |
| * any grace periods that elapsed while the CPU was idle, and if any |
| * callbacks are now ready to invoke, initiate invocation. |
| */ |
| static void rcu_cleanup_after_idle(int cpu) |
| { |
| struct rcu_data *rdp; |
| struct rcu_state *rsp; |
| |
| if (rcu_is_nocb_cpu(cpu)) |
| return; |
| rcu_try_advance_all_cbs(); |
| for_each_rcu_flavor(rsp) { |
| rdp = per_cpu_ptr(rsp->rda, cpu); |
| if (cpu_has_callbacks_ready_to_invoke(rdp)) |
| invoke_rcu_core(); |
| } |
| } |
| |
| /* |
| * Keep a running count of the number of non-lazy callbacks posted |
| * on this CPU. This running counter (which is never decremented) allows |
| * rcu_prepare_for_idle() to detect when something out of the idle loop |
| * posts a callback, even if an equal number of callbacks are invoked. |
| * Of course, callbacks should only be posted from within a trace event |
| * designed to be called from idle or from within RCU_NONIDLE(). |
| */ |
| static void rcu_idle_count_callbacks_posted(void) |
| { |
| __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
| } |
| |
| /* |
| * Data for flushing lazy RCU callbacks at OOM time. |
| */ |
| static atomic_t oom_callback_count; |
| static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); |
| |
| /* |
| * RCU OOM callback -- decrement the outstanding count and deliver the |
| * wake-up if we are the last one. |
| */ |
| static void rcu_oom_callback(struct rcu_head *rhp) |
| { |
| if (atomic_dec_and_test(&oom_callback_count)) |
| wake_up(&oom_callback_wq); |
| } |
| |
| /* |
| * Post an rcu_oom_notify callback on the current CPU if it has at |
| * least one lazy callback. This will unnecessarily post callbacks |
| * to CPUs that already have a non-lazy callback at the end of their |
| * callback list, but this is an infrequent operation, so accept some |
| * extra overhead to keep things simple. |
| */ |
| static void rcu_oom_notify_cpu(void *unused) |
| { |
| struct rcu_state *rsp; |
| struct rcu_data *rdp; |
| |
| for_each_rcu_flavor(rsp) { |
| rdp = __this_cpu_ptr(rsp->rda); |
| if (rdp->qlen_lazy != 0) { |
| atomic_inc(&oom_callback_count); |
| rsp->call(&rdp->oom_head, rcu_oom_callback); |
| } |
| } |
| } |
| |
| /* |
| * If low on memory, ensure that each CPU has a non-lazy callback. |
| * This will wake up CPUs that have only lazy callbacks, in turn |
| * ensuring that they free up the corresponding memory in a timely manner. |
| * Because an uncertain amount of memory will be freed in some uncertain |
| * timeframe, we do not claim to have freed anything. |
| */ |
| static int rcu_oom_notify(struct notifier_block *self, |
| unsigned long notused, void *nfreed) |
| { |
| int cpu; |
| |
| /* Wait for callbacks from earlier instance to complete. */ |
| wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); |
| |
| /* |
| * Prevent premature wakeup: ensure that all increments happen |
| * before there is a chance of the counter reaching zero. |
| */ |
| atomic_set(&oom_callback_count, 1); |
| |
| get_online_cpus(); |
| for_each_online_cpu(cpu) { |
| smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); |
| cond_resched(); |
| } |
| put_online_cpus(); |
| |
| /* Unconditionally decrement: no need to wake ourselves up. */ |
| atomic_dec(&oom_callback_count); |
| |
| return NOTIFY_OK; |
| } |
| |
| static struct notifier_block rcu_oom_nb = { |
| .notifier_call = rcu_oom_notify |
| }; |
| |
| static int __init rcu_register_oom_notifier(void) |
| { |
| register_oom_notifier(&rcu_oom_nb); |
| return 0; |
| } |
| early_initcall(rcu_register_oom_notifier); |
| |
| #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
| |
| #ifdef CONFIG_RCU_CPU_STALL_INFO |
| |
| #ifdef CONFIG_RCU_FAST_NO_HZ |
| |
| static void print_cpu_stall_fast_no_hz(char *cp, int cpu) |
| { |
| struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
| unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; |
| |
| sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", |
| rdtp->last_accelerate & 0xffff, jiffies & 0xffff, |
| ulong2long(nlpd), |
| rdtp->all_lazy ? 'L' : '.', |
| rdtp->tick_nohz_enabled_snap ? '.' : 'D'); |
| } |
| |
| #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ |
| |
| static void print_cpu_stall_fast_no_hz(char *cp, int cpu) |
| { |
| *cp = '\0'; |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ |
| |
| /* Initiate the stall-info list. */ |
| static void print_cpu_stall_info_begin(void) |
| { |
| printk(KERN_CONT "\n"); |
| } |
| |
| /* |
| * Print out diagnostic information for the specified stalled CPU. |
| * |
| * If the specified CPU is aware of the current RCU grace period |
| * (flavor specified by rsp), then print the number of scheduling |
| * clock interrupts the CPU has taken during the time that it has |
| * been aware. Otherwise, print the number of RCU grace periods |
| * that this CPU is ignorant of, for example, "1" if the CPU was |
| * aware of the previous grace period. |
| * |
| * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. |
| */ |
| static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) |
| { |
| char fast_no_hz[72]; |
| struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); |
| struct rcu_dynticks *rdtp = rdp->dynticks; |
| char *ticks_title; |
| unsigned long ticks_value; |
| |
| if (rsp->gpnum == rdp->gpnum) { |
| ticks_title = "ticks this GP"; |
| ticks_value = rdp->ticks_this_gp; |
| } else { |
| ticks_title = "GPs behind"; |
| ticks_value = rsp->gpnum - rdp->gpnum; |
| } |
| print_cpu_stall_fast_no_hz(fast_no_hz, cpu); |
| printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n", |
| cpu, ticks_value, ticks_title, |
| atomic_read(&rdtp->dynticks) & 0xfff, |
| rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, |
| rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
| fast_no_hz); |
| } |
| |
| /* Terminate the stall-info list. */ |
| static void print_cpu_stall_info_end(void) |
| { |
| printk(KERN_ERR "\t"); |
| } |
| |
| /* Zero ->ticks_this_gp for all flavors of RCU. */ |
| static void zero_cpu_stall_ticks(struct rcu_data *rdp) |
| { |
| rdp->ticks_this_gp = 0; |
| rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
| } |
| |
| /* Increment ->ticks_this_gp for all flavors of RCU. */ |
| static void increment_cpu_stall_ticks(void) |
| { |
| struct rcu_state *rsp; |
| |
| for_each_rcu_flavor(rsp) |
| __this_cpu_ptr(rsp->rda)->ticks_this_gp++; |
| } |
| |
| #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ |
| |
| static void print_cpu_stall_info_begin(void) |
| { |
| printk(KERN_CONT " {"); |
| } |
| |
| static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) |
| { |
| printk(KERN_CONT " %d", cpu); |
| } |
| |
| static void print_cpu_stall_info_end(void) |
| { |
| printk(KERN_CONT "} "); |
| } |
| |
| static void zero_cpu_stall_ticks(struct rcu_data *rdp) |
| { |
| } |
| |
| static void increment_cpu_stall_ticks(void) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ |
| |
| #ifdef CONFIG_RCU_NOCB_CPU |
| |
| /* |
| * Offload callback processing from the boot-time-specified set of CPUs |
| * specified by rcu_nocb_mask. For each CPU in the set, there is a |
| * kthread created that pulls the callbacks from the corresponding CPU, |
| * waits for a grace period to elapse, and invokes the callbacks. |
| * The no-CBs CPUs do a wake_up() on their kthread when they insert |
| * a callback into any empty list, unless the rcu_nocb_poll boot parameter |
| * has been specified, in which case each kthread actively polls its |
| * CPU. (Which isn't so great for energy efficiency, but which does |
| * reduce RCU's overhead on that CPU.) |
| * |
| * This is intended to be used in conjunction with Frederic Weisbecker's |
| * adaptive-idle work, which would seriously reduce OS jitter on CPUs |
| * running CPU-bound user-mode computations. |
| * |
| * Offloading of callback processing could also in theory be used as |
| * an energy-efficiency measure because CPUs with no RCU callbacks |
| * queued are more aggressive about entering dyntick-idle mode. |
| */ |
| |
| |
| /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ |
| static int __init rcu_nocb_setup(char *str) |
| { |
| alloc_bootmem_cpumask_var(&rcu_nocb_mask); |
| have_rcu_nocb_mask = true; |
| cpulist_parse(str, rcu_nocb_mask); |
| return 1; |
| } |
| __setup("rcu_nocbs=", rcu_nocb_setup); |
| |
| static int __init parse_rcu_nocb_poll(char *arg) |
| { |
| rcu_nocb_poll = 1; |
| return 0; |
| } |
| early_param("rcu_nocb_poll", parse_rcu_nocb_poll); |
| |
| /* |
| * Do any no-CBs CPUs need another grace period? |
| * |
| * 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_nocb_needs_gp(struct rcu_state *rsp) |
| { |
| struct rcu_node *rnp = rcu_get_root(rsp); |
| |
| return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1]; |
| } |
| |
| /* |
| * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended |
| * grace period. |
| */ |
| static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
| { |
| wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); |
| } |
| |
| /* |
| * Set the root rcu_node structure's ->need_future_gp field |
| * based on the sum of those of all rcu_node structures. This does |
| * double-count the root rcu_node structure's requests, but this |
| * is necessary to handle the possibility of a rcu_nocb_kthread() |
| * having awakened during the time that the rcu_node structures |
| * were being updated for the end of the previous grace period. |
| */ |
| static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
| { |
| rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; |
| } |
| |
| static void rcu_init_one_nocb(struct rcu_node *rnp) |
| { |
| init_waitqueue_head(&rnp->nocb_gp_wq[0]); |
| init_waitqueue_head(&rnp->nocb_gp_wq[1]); |
| } |
| |
| /* Is the specified CPU a no-CPUs CPU? */ |
| bool rcu_is_nocb_cpu(int cpu) |
| { |
| if (have_rcu_nocb_mask) |
| return cpumask_test_cpu(cpu, rcu_nocb_mask); |
| return false; |
| } |
| |
| /* |
| * Enqueue the specified string of rcu_head structures onto the specified |
| * CPU's no-CBs lists. The CPU is specified by rdp, the head of the |
| * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy |
| * counts are supplied by rhcount and rhcount_lazy. |
| * |
| * If warranted, also wake up the kthread servicing this CPUs queues. |
| */ |
| static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, |
| struct rcu_head *rhp, |
| struct rcu_head **rhtp, |
| int rhcount, int rhcount_lazy) |
| { |
| int len; |
| struct rcu_head **old_rhpp; |
| struct task_struct *t; |
| |
| /* Enqueue the callback on the nocb list and update counts. */ |
| old_rhpp = xchg(&rdp->nocb_tail, rhtp); |
| ACCESS_ONCE(*old_rhpp) = rhp; |
| atomic_long_add(rhcount, &rdp->nocb_q_count); |
| atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); |
| |
| /* If we are not being polled and there is a kthread, awaken it ... */ |
| t = ACCESS_ONCE(rdp->nocb_kthread); |
| if (rcu_nocb_poll | !t) |
| return; |
| len = atomic_long_read(&rdp->nocb_q_count); |
| if (old_rhpp == &rdp->nocb_head) { |
| wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */ |
| rdp->qlen_last_fqs_check = 0; |
| } else if (len > rdp->qlen_last_fqs_check + qhimark) { |
| wake_up_process(t); /* ... or if many callbacks queued. */ |
| rdp->qlen_last_fqs_check = LONG_MAX / 2; |
| } |
| return; |
| } |
| |
| /* |
| * This is a helper for __call_rcu(), which invokes this when the normal |
| * callback queue is inoperable. If this is not a no-CBs CPU, this |
| * function returns failure back to __call_rcu(), which can complain |
| * appropriately. |
| * |
| * Otherwise, this function queues the callback where the corresponding |
| * "rcuo" kthread can find it. |
| */ |
| static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
| bool lazy) |
| { |
| |
| if (!rcu_is_nocb_cpu(rdp->cpu)) |
| return 0; |
| __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy); |
| if (__is_kfree_rcu_offset((unsigned long)rhp->func)) |
| trace_rcu_kfree_callback(rdp->rsp->name, rhp, |
| (unsigned long)rhp->func, |
| rdp->qlen_lazy, rdp->qlen); |
| else |
| trace_rcu_callback(rdp->rsp->name, rhp, |
| rdp->qlen_lazy, rdp->qlen); |
| return 1; |
| } |
| |
| /* |
| * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is |
| * not a no-CBs CPU. |
| */ |
| static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, |
| struct rcu_data *rdp) |
| { |
| long ql = rsp->qlen; |
| long qll = rsp->qlen_lazy; |
| |
| /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ |
| if (!rcu_is_nocb_cpu(smp_processor_id())) |
| return 0; |
| rsp->qlen = 0; |
| rsp->qlen_lazy = 0; |
| |
| /* First, enqueue the donelist, if any. This preserves CB ordering. */ |
| if (rsp->orphan_donelist != NULL) { |
| __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, |
| rsp->orphan_donetail, ql, qll); |
| ql = qll = 0; |
| rsp->orphan_donelist = NULL; |
| rsp->orphan_donetail = &rsp->orphan_donelist; |
| } |
| if (rsp->orphan_nxtlist != NULL) { |
| __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, |
| rsp->orphan_nxttail, ql, qll); |
| ql = qll = 0; |
| rsp->orphan_nxtlist = NULL; |
| rsp->orphan_nxttail = &rsp->orphan_nxtlist; |
| } |
| return 1; |
| } |
| |
| /* |
| * If necessary, kick off a new grace period, and either way wait |
| * for a subsequent grace period to complete. |
| */ |
| static void rcu_nocb_wait_gp(struct rcu_data *rdp) |
| { |
| unsigned long c; |
| bool d; |
| unsigned long flags; |
| struct rcu_node *rnp = rdp->mynode; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| c = rcu_start_future_gp(rnp, rdp); |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| |
| /* |
| * Wait for the grace period. Do so interruptibly to avoid messing |
| * up the load average. |
| */ |
| trace_rcu_future_gp(rnp, rdp, c, "StartWait"); |
| for (;;) { |
| wait_event_interruptible( |
| rnp->nocb_gp_wq[c & 0x1], |
| (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c))); |
| if (likely(d)) |
| break; |
| flush_signals(current); |
| trace_rcu_future_gp(rnp, rdp, c, "ResumeWait"); |
| } |
| trace_rcu_future_gp(rnp, rdp, c, "EndWait"); |
| smp_mb(); /* Ensure that CB invocation happens after GP end. */ |
| } |
| |
| /* |
| * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes |
| * callbacks queued by the corresponding no-CBs CPU. |
| */ |
| static int rcu_nocb_kthread(void *arg) |
| { |
| int c, cl; |
| struct rcu_head *list; |
| struct rcu_head *next; |
| struct rcu_head **tail; |
| struct rcu_data *rdp = arg; |
| |
| /* Each pass through this loop invokes one batch of callbacks */ |
| for (;;) { |
| /* If not polling, wait for next batch of callbacks. */ |
| if (!rcu_nocb_poll) |
| wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head); |
| list = ACCESS_ONCE(rdp->nocb_head); |
| if (!list) { |
| schedule_timeout_interruptible(1); |
| flush_signals(current); |
| continue; |
| } |
| |
| /* |
| * Extract queued callbacks, update counts, and wait |
| * for a grace period to elapse. |
| */ |
| ACCESS_ONCE(rdp->nocb_head) = NULL; |
| tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); |
| c = atomic_long_xchg(&rdp->nocb_q_count, 0); |
| cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); |
| ACCESS_ONCE(rdp->nocb_p_count) += c; |
| ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl; |
| rcu_nocb_wait_gp(rdp); |
| |
| /* Each pass through the following loop invokes a callback. */ |
| trace_rcu_batch_start(rdp->rsp->name, cl, c, -1); |
| c = cl = 0; |
| while (list) { |
| next = list->next; |
| /* Wait for enqueuing to complete, if needed. */ |
| while (next == NULL && &list->next != tail) { |
| schedule_timeout_interruptible(1); |
| next = list->next; |
| } |
| debug_rcu_head_unqueue(list); |
| local_bh_disable(); |
| if (__rcu_reclaim(rdp->rsp->name, list)) |
| cl++; |
| c++; |
| local_bh_enable(); |
| list = next; |
| } |
| trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); |
| ACCESS_ONCE(rdp->nocb_p_count) -= c; |
| ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl; |
| rdp->n_nocbs_invoked += c; |
| } |
| return 0; |
| } |
| |
| /* Initialize per-rcu_data variables for no-CBs CPUs. */ |
| static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
| { |
| rdp->nocb_tail = &rdp->nocb_head; |
| init_waitqueue_head(&rdp->nocb_wq); |
| } |
| |
| /* Create a kthread for each RCU flavor for each no-CBs CPU. */ |
| static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) |
| { |
| int cpu; |
| struct rcu_data *rdp; |
| struct task_struct *t; |
| |
| if (rcu_nocb_mask == NULL) |
| return; |
| for_each_cpu(cpu, rcu_nocb_mask) { |
| rdp = per_cpu_ptr(rsp->rda, cpu); |
| t = kthread_run(rcu_nocb_kthread, rdp, |
| "rcuo%c/%d", rsp->abbr, cpu); |
| BUG_ON(IS_ERR(t)); |
| ACCESS_ONCE(rdp->nocb_kthread) = t; |
| } |
| } |
| |
| /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ |
| static bool init_nocb_callback_list(struct rcu_data *rdp) |
| { |
| if (rcu_nocb_mask == NULL || |
| !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask)) |
| return false; |
| rdp->nxttail[RCU_NEXT_TAIL] = NULL; |
| return true; |
| } |
| |
| #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
| |
| static int rcu_nocb_needs_gp(struct rcu_state *rsp) |
| { |
| return 0; |
| } |
| |
| static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
| { |
| } |
| |
| static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
| { |
| } |
| |
| static void rcu_init_one_nocb(struct rcu_node *rnp) |
| { |
| } |
| |
| static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
| bool lazy) |
| { |
| return 0; |
| } |
| |
| static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, |
| struct rcu_data *rdp) |
| { |
| return 0; |
| } |
| |
| static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
| { |
| } |
| |
| static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) |
| { |
| } |
| |
| static bool init_nocb_callback_list(struct rcu_data *rdp) |
| { |
| return false; |
| } |
| |
| #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |
| |
| /* |
| * An adaptive-ticks CPU can potentially execute in kernel mode for an |
| * arbitrarily long period of time with the scheduling-clock tick turned |
| * off. RCU will be paying attention to this CPU because it is in the |
| * kernel, but the CPU cannot be guaranteed to be executing the RCU state |
| * machine because the scheduling-clock tick has been disabled. Therefore, |
| * if an adaptive-ticks CPU is failing to respond to the current grace |
| * period and has not be idle from an RCU perspective, kick it. |
| */ |
| static void rcu_kick_nohz_cpu(int cpu) |
| { |
| #ifdef CONFIG_NO_HZ_FULL |
| if (tick_nohz_full_cpu(cpu)) |
| smp_send_reschedule(cpu); |
| #endif /* #ifdef CONFIG_NO_HZ_FULL */ |
| } |