| /* |
| * 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/stop_machine.h> |
| |
| /* |
| * 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 "\tVerbose stalled-CPUs detection is disabled.\n"); |
| #endif |
| #if NUM_RCU_LVL_4 != 0 |
| printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n"); |
| #endif |
| } |
| |
| #ifdef CONFIG_TREE_PREEMPT_RCU |
| |
| struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); |
| 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, 0); |
| } |
| 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); |
| |
| rdp->passed_quiesc_completed = rdp->gpnum - 1; |
| barrier(); |
| rdp->passed_quiesc = 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 && |
| (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; |
| } |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| /* |
| * 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); |
| } |
| |
| /* |
| * Tree-preemptible RCU implementation for rcu_read_lock(). |
| * Just increment ->rcu_read_lock_nesting, shared state will be updated |
| * if we block. |
| */ |
| void __rcu_read_lock(void) |
| { |
| current->rcu_read_lock_nesting++; |
| barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ |
| } |
| EXPORT_SYMBOL_GPL(__rcu_read_lock); |
| |
| /* |
| * 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. |
| */ |
| static void rcu_read_unlock_special(struct task_struct *t) |
| { |
| int empty; |
| int empty_exp; |
| unsigned long flags; |
| struct list_head *np; |
| 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()) { |
| 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); |
| 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; |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| t->rcu_blocked_node = NULL; |
| |
| /* |
| * 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. |
| */ |
| if (empty) |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| else |
| rcu_report_unblock_qs_rnp(rnp, flags); |
| |
| #ifdef CONFIG_RCU_BOOST |
| /* Unboost if we were boosted. */ |
| if (special & RCU_READ_UNLOCK_BOOSTED) { |
| t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; |
| rt_mutex_unlock(t->rcu_boost_mutex); |
| t->rcu_boost_mutex = NULL; |
| } |
| #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 && !rcu_preempted_readers_exp(rnp)) |
| rcu_report_exp_rnp(&rcu_preempt_state, rnp); |
| } else { |
| local_irq_restore(flags); |
| } |
| } |
| |
| /* |
| * Tree-preemptible RCU implementation for rcu_read_unlock(). |
| * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
| * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
| * invoke rcu_read_unlock_special() to clean up after a context switch |
| * in an RCU read-side critical section and other special cases. |
| */ |
| void __rcu_read_unlock(void) |
| { |
| struct task_struct *t = current; |
| |
| barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ |
| --t->rcu_read_lock_nesting; |
| barrier(); /* decrement before load of ->rcu_read_unlock_special */ |
| if (t->rcu_read_lock_nesting == 0 && |
| unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
| rcu_read_unlock_special(t); |
| #ifdef CONFIG_PROVE_LOCKING |
| WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); |
| #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
| } |
| EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
| |
| #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; |
| |
| if (!rcu_preempt_blocked_readers_cgp(rnp)) |
| return; |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| 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 */ |
| |
| /* |
| * Scan the current list of tasks blocked within RCU read-side critical |
| * sections, printing out the tid of each. |
| */ |
| static void rcu_print_task_stall(struct rcu_node *rnp) |
| { |
| struct task_struct *t; |
| |
| if (!rcu_preempt_blocked_readers_cgp(rnp)) |
| 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) |
| printk(" P%d", t->pid); |
| } |
| |
| /* |
| * Suppress preemptible RCU's CPU stall warnings by pushing the |
| * time of the next stall-warning message comfortably far into the |
| * future. |
| */ |
| static void rcu_preempt_stall_reset(void) |
| { |
| rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2; |
| } |
| |
| /* |
| * 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)) |
| 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 */ |
| } |
| |
| #ifdef CONFIG_RCU_BOOST |
| /* In case root is being boosted and leaf is not. */ |
| 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->gp_tasks; |
| raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
| #endif /* #ifdef CONFIG_RCU_BOOST */ |
| |
| rnp->gp_tasks = NULL; |
| rnp->exp_tasks = NULL; |
| return retval; |
| } |
| |
| /* |
| * Do CPU-offline processing for preemptible RCU. |
| */ |
| static void rcu_preempt_offline_cpu(int cpu) |
| { |
| __rcu_offline_cpu(cpu, &rcu_preempt_state); |
| } |
| |
| #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 (per_cpu(rcu_preempt_data, cpu).qs_pending) |
| t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
| } |
| |
| /* |
| * Process callbacks for preemptible RCU. |
| */ |
| static void rcu_preempt_process_callbacks(void) |
| { |
| __rcu_process_callbacks(&rcu_preempt_state, |
| &__get_cpu_var(rcu_preempt_data)); |
| } |
| |
| /* |
| * 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); |
| } |
| EXPORT_SYMBOL_GPL(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. |
| */ |
| void synchronize_rcu(void) |
| { |
| struct rcu_synchronize rcu; |
| |
| if (!rcu_scheduler_active) |
| return; |
| |
| init_rcu_head_on_stack(&rcu.head); |
| init_completion(&rcu.completion); |
| /* Will wake me after RCU finished. */ |
| call_rcu(&rcu.head, wakeme_after_rcu); |
| /* Wait for it. */ |
| wait_for_completion(&rcu.completion); |
| destroy_rcu_head_on_stack(&rcu.head); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_rcu); |
| |
| static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
| static 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!) |
| * |
| * Caller must hold sync_rcu_preempt_exp_mutex. |
| */ |
| static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) |
| { |
| unsigned long flags; |
| unsigned long mask; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| for (;;) { |
| if (!sync_rcu_preempt_exp_done(rnp)) |
| break; |
| if (rnp->parent == NULL) { |
| 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; |
| } |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| /* |
| * 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 rsp->onofflock. |
| */ |
| static void |
| sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) |
| { |
| int must_wait = 0; |
| |
| raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
| if (!list_empty(&rnp->blkd_tasks)) { |
| rnp->exp_tasks = rnp->blkd_tasks.next; |
| rcu_initiate_boost(rnp); |
| must_wait = 1; |
| } |
| raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
| if (!must_wait) |
| rcu_report_exp_rnp(rsp, rnp); |
| } |
| |
| /* |
| * 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. |
| */ |
| void synchronize_rcu_expedited(void) |
| { |
| unsigned long flags; |
| struct rcu_node *rnp; |
| struct rcu_state *rsp = &rcu_preempt_state; |
| 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. */ |
| |
| /* |
| * 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 (trycount++ < 10) |
| udelay(trycount * num_online_cpus()); |
| else { |
| synchronize_rcu(); |
| return; |
| } |
| if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) |
| goto mb_ret; /* Others did our work for us. */ |
| } |
| if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) |
| goto unlock_mb_ret; /* Others did our work for us. */ |
| |
| /* force all RCU readers onto ->blkd_tasks lists. */ |
| synchronize_sched_expedited(); |
| |
| raw_spin_lock_irqsave(&rsp->onofflock, flags); |
| |
| /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
| rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { |
| raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
| rnp->expmask = rnp->qsmaskinit; |
| raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
| } |
| |
| /* 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)); |
| |
| raw_spin_unlock_irqrestore(&rsp->onofflock, flags); |
| |
| /* 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); |
| |
| /* |
| * Check to see if there is any immediate preemptible-RCU-related work |
| * to be done. |
| */ |
| static int rcu_preempt_pending(int cpu) |
| { |
| return __rcu_pending(&rcu_preempt_state, |
| &per_cpu(rcu_preempt_data, cpu)); |
| } |
| |
| /* |
| * Does preemptible RCU need the CPU to stay out of dynticks mode? |
| */ |
| static int rcu_preempt_needs_cpu(int cpu) |
| { |
| return !!per_cpu(rcu_preempt_data, cpu).nxtlist; |
| } |
| |
| /** |
| * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. |
| */ |
| void rcu_barrier(void) |
| { |
| _rcu_barrier(&rcu_preempt_state, call_rcu); |
| } |
| EXPORT_SYMBOL_GPL(rcu_barrier); |
| |
| /* |
| * Initialize preemptible RCU's per-CPU data. |
| */ |
| static void __cpuinit rcu_preempt_init_percpu_data(int cpu) |
| { |
| rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); |
| } |
| |
| /* |
| * Move preemptible RCU's callbacks from dying CPU to other online CPU. |
| */ |
| static void rcu_preempt_send_cbs_to_online(void) |
| { |
| rcu_send_cbs_to_online(&rcu_preempt_state); |
| } |
| |
| /* |
| * Initialize preemptible RCU's state structures. |
| */ |
| static void __init __rcu_init_preempt(void) |
| { |
| rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
| } |
| |
| /* |
| * Check for a task exiting while in a preemptible-RCU read-side |
| * critical section, clean up if so. No need to issue warnings, |
| * as debug_check_no_locks_held() already does this if lockdep |
| * is enabled. |
| */ |
| void exit_rcu(void) |
| { |
| struct task_struct *t = current; |
| |
| if (t->rcu_read_lock_nesting == 0) |
| return; |
| t->rcu_read_lock_nesting = 1; |
| __rcu_read_unlock(); |
| } |
| |
| #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 void rcu_print_task_stall(struct rcu_node *rnp) |
| { |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, there is no need to suppress |
| * its CPU stall warnings. |
| */ |
| static void rcu_preempt_stall_reset(void) |
| { |
| } |
| |
| /* |
| * 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; |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, it never needs CPU-offline |
| * processing. |
| */ |
| static void rcu_preempt_offline_cpu(int cpu) |
| { |
| } |
| |
| #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) |
| { |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, it never has any callbacks |
| * to process. |
| */ |
| static void rcu_preempt_process_callbacks(void) |
| { |
| } |
| |
| /* |
| * 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) |
| { |
| return; |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| /* |
| * Because preemptible RCU does not exist, it never has any work to do. |
| */ |
| static int rcu_preempt_pending(int cpu) |
| { |
| return 0; |
| } |
| |
| /* |
| * Because preemptible RCU does not exist, it never needs any CPU. |
| */ |
| static int rcu_preempt_needs_cpu(int cpu) |
| { |
| return 0; |
| } |
| |
| /* |
| * 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, there is no per-CPU |
| * data to initialize. |
| */ |
| static void __cpuinit rcu_preempt_init_percpu_data(int cpu) |
| { |
| } |
| |
| /* |
| * Because there is no preemptible RCU, there are no callbacks to move. |
| */ |
| static void rcu_preempt_send_cbs_to_online(void) |
| { |
| } |
| |
| /* |
| * 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 */ |
| |
| /* |
| * 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; |
| t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; |
| 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 rnp->exp_tasks != NULL || rnp->boost_tasks != NULL; |
| } |
| |
| /* |
| * Timer handler to initiate waking up of boost kthreads that |
| * have yielded the CPU due to excessive numbers of tasks to |
| * boost. We wake up the per-rcu_node kthread, which in turn |
| * will wake up the booster kthread. |
| */ |
| static void rcu_boost_kthread_timer(unsigned long arg) |
| { |
| unsigned long flags; |
| struct rcu_node *rnp = (struct rcu_node *)arg; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| invoke_rcu_node_kthread(rnp); |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| } |
| |
| /* |
| * 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; |
| |
| for (;;) { |
| rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
| wait_event_interruptible(rnp->boost_wq, rnp->boost_tasks || |
| rnp->exp_tasks || |
| kthread_should_stop()); |
| if (kthread_should_stop()) |
| break; |
| rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
| more2boost = rcu_boost(rnp); |
| if (more2boost) |
| spincnt++; |
| else |
| spincnt = 0; |
| if (spincnt > 10) { |
| rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp); |
| spincnt = 0; |
| } |
| } |
| rnp->boost_kthread_status = RCU_KTHREAD_STOPPED; |
| 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. |
| */ |
| static void rcu_initiate_boost(struct rcu_node *rnp) |
| { |
| struct task_struct *t; |
| |
| if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
| rnp->n_balk_exp_gp_tasks++; |
| 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; |
| t = rnp->boost_kthread_task; |
| if (t != NULL) |
| wake_up_process(t); |
| } else |
| rcu_initiate_boost_trace(rnp); |
| } |
| |
| /* |
| * Set the affinity of the boost kthread. The CPU-hotplug locks are |
| * held, so no one should be messing with the existence of the boost |
| * kthread. |
| */ |
| static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, |
| cpumask_var_t cm) |
| { |
| struct task_struct *t; |
| |
| t = rnp->boost_kthread_task; |
| if (t != NULL) |
| set_cpus_allowed_ptr(rnp->boost_kthread_task, cm); |
| } |
| |
| #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; |
| } |
| |
| /* |
| * Initialize the RCU-boost waitqueue. |
| */ |
| static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp) |
| { |
| init_waitqueue_head(&rnp->boost_wq); |
| } |
| |
| /* |
| * 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) |
| { |
| unsigned long flags; |
| struct sched_param sp; |
| struct task_struct *t; |
| |
| if (&rcu_preempt_state != rsp) |
| return 0; |
| 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); |
| wake_up_process(t); |
| sp.sched_priority = RCU_KTHREAD_PRIO; |
| sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
| return 0; |
| } |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| |
| static void rcu_stop_boost_kthread(struct rcu_node *rnp) |
| { |
| unsigned long flags; |
| struct task_struct *t; |
| |
| raw_spin_lock_irqsave(&rnp->lock, flags); |
| t = rnp->boost_kthread_task; |
| rnp->boost_kthread_task = NULL; |
| raw_spin_unlock_irqrestore(&rnp->lock, flags); |
| if (t != NULL) |
| kthread_stop(t); |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| #else /* #ifdef CONFIG_RCU_BOOST */ |
| |
| static void rcu_initiate_boost(struct rcu_node *rnp) |
| { |
| } |
| |
| static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, |
| cpumask_var_t cm) |
| { |
| } |
| |
| static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
| { |
| } |
| |
| static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp) |
| { |
| } |
| |
| static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
| struct rcu_node *rnp, |
| int rnp_index) |
| { |
| return 0; |
| } |
| |
| #ifdef CONFIG_HOTPLUG_CPU |
| |
| static void rcu_stop_boost_kthread(struct rcu_node *rnp) |
| { |
| } |
| |
| #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
| |
| #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
| |
| #ifndef CONFIG_SMP |
| |
| void synchronize_sched_expedited(void) |
| { |
| cond_resched(); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_sched_expedited); |
| |
| #else /* #ifndef CONFIG_SMP */ |
| |
| static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); |
| static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); |
| |
| static int synchronize_sched_expedited_cpu_stop(void *data) |
| { |
| /* |
| * There must be a full memory barrier on each affected CPU |
| * between the time that try_stop_cpus() is called and the |
| * time that it returns. |
| * |
| * In the current initial implementation of cpu_stop, the |
| * above condition is already met when the control reaches |
| * this point and the following smp_mb() is not strictly |
| * necessary. Do smp_mb() anyway for documentation and |
| * robustness against future implementation changes. |
| */ |
| smp_mb(); /* See above comment block. */ |
| return 0; |
| } |
| |
| /* |
| * Wait for an rcu-sched grace period to elapse, but use "big hammer" |
| * approach to force grace period to end quickly. This consumes |
| * significant time on all CPUs, and is thus not recommended for |
| * any sort of common-case code. |
| * |
| * Note that it is illegal to call this function while holding any |
| * lock that is acquired by a CPU-hotplug notifier. Failing to |
| * observe this restriction will result in deadlock. |
| * |
| * This implementation can be thought of as an application of ticket |
| * locking to RCU, with sync_sched_expedited_started and |
| * sync_sched_expedited_done taking on the roles of the halves |
| * of the ticket-lock word. Each task atomically increments |
| * sync_sched_expedited_started upon entry, snapshotting the old value, |
| * then attempts to stop all the CPUs. If this succeeds, then each |
| * CPU will have executed a context switch, resulting in an RCU-sched |
| * grace period. We are then done, so we use atomic_cmpxchg() to |
| * update sync_sched_expedited_done to match our snapshot -- but |
| * only if someone else has not already advanced past our snapshot. |
| * |
| * On the other hand, if try_stop_cpus() fails, we check the value |
| * of sync_sched_expedited_done. If it has advanced past our |
| * initial snapshot, then someone else must have forced a grace period |
| * some time after we took our snapshot. In this case, our work is |
| * done for us, and we can simply return. Otherwise, we try again, |
| * but keep our initial snapshot for purposes of checking for someone |
| * doing our work for us. |
| * |
| * If we fail too many times in a row, we fall back to synchronize_sched(). |
| */ |
| void synchronize_sched_expedited(void) |
| { |
| int firstsnap, s, snap, trycount = 0; |
| |
| /* Note that atomic_inc_return() implies full memory barrier. */ |
| firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); |
| get_online_cpus(); |
| |
| /* |
| * Each pass through the following loop attempts to force a |
| * context switch on each CPU. |
| */ |
| while (try_stop_cpus(cpu_online_mask, |
| synchronize_sched_expedited_cpu_stop, |
| NULL) == -EAGAIN) { |
| put_online_cpus(); |
| |
| /* No joy, try again later. Or just synchronize_sched(). */ |
| if (trycount++ < 10) |
| udelay(trycount * num_online_cpus()); |
| else { |
| synchronize_sched(); |
| return; |
| } |
| |
| /* Check to see if someone else did our work for us. */ |
| s = atomic_read(&sync_sched_expedited_done); |
| if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { |
| smp_mb(); /* ensure test happens before caller kfree */ |
| return; |
| } |
| |
| /* |
| * Refetching sync_sched_expedited_started allows later |
| * callers to piggyback on our grace period. We subtract |
| * 1 to get the same token that the last incrementer got. |
| * We retry after they started, so our grace period works |
| * for them, and they started after our first try, so their |
| * grace period works for us. |
| */ |
| get_online_cpus(); |
| snap = atomic_read(&sync_sched_expedited_started) - 1; |
| smp_mb(); /* ensure read is before try_stop_cpus(). */ |
| } |
| |
| /* |
| * Everyone up to our most recent fetch is covered by our grace |
| * period. Update the counter, but only if our work is still |
| * relevant -- which it won't be if someone who started later |
| * than we did beat us to the punch. |
| */ |
| do { |
| s = atomic_read(&sync_sched_expedited_done); |
| if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { |
| smp_mb(); /* ensure test happens before caller kfree */ |
| break; |
| } |
| } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); |
| |
| put_online_cpus(); |
| } |
| EXPORT_SYMBOL_GPL(synchronize_sched_expedited); |
| |
| #endif /* #else #ifndef CONFIG_SMP */ |
| |
| #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 have preemptible RCU, just check whether this CPU needs |
| * any flavor of RCU. Do not chew up lots of CPU cycles with preemption |
| * disabled in a most-likely vain attempt to cause RCU not to need this CPU. |
| */ |
| int rcu_needs_cpu(int cpu) |
| { |
| return rcu_needs_cpu_quick_check(cpu); |
| } |
| |
| /* |
| * Check to see if we need to continue a callback-flush operations to |
| * allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle |
| * entry is not configured, so we never do need to. |
| */ |
| static void rcu_needs_cpu_flush(void) |
| { |
| } |
| |
| #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
| |
| #define RCU_NEEDS_CPU_FLUSHES 5 |
| static DEFINE_PER_CPU(int, rcu_dyntick_drain); |
| static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); |
| |
| /* |
| * 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 are not supporting preemptible RCU, attempt to accelerate |
| * any current grace periods so that RCU no longer needs this CPU, but |
| * only if all other CPUs are already in dynticks-idle mode. This will |
| * allow the CPU cores to be powered down immediately, as opposed to after |
| * waiting many milliseconds for grace periods to elapse. |
| * |
| * Because it is not legal to invoke rcu_process_callbacks() with irqs |
| * disabled, we do one pass of force_quiescent_state(), then do a |
| * invoke_rcu_cpu_kthread() to cause rcu_process_callbacks() to be invoked |
| * later. The per-cpu rcu_dyntick_drain variable controls the sequencing. |
| */ |
| int rcu_needs_cpu(int cpu) |
| { |
| int c = 0; |
| int snap; |
| int thatcpu; |
| |
| /* Check for being in the holdoff period. */ |
| if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) |
| return rcu_needs_cpu_quick_check(cpu); |
| |
| /* Don't bother unless we are the last non-dyntick-idle CPU. */ |
| for_each_online_cpu(thatcpu) { |
| if (thatcpu == cpu) |
| continue; |
| snap = atomic_add_return(0, &per_cpu(rcu_dynticks, |
| thatcpu).dynticks); |
| smp_mb(); /* Order sampling of snap with end of grace period. */ |
| if ((snap & 0x1) != 0) { |
| per_cpu(rcu_dyntick_drain, cpu) = 0; |
| per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; |
| return rcu_needs_cpu_quick_check(cpu); |
| } |
| } |
| |
| /* Check and update the rcu_dyntick_drain sequencing. */ |
| if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { |
| /* First time through, initialize the counter. */ |
| per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; |
| } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { |
| /* We have hit the limit, so time to give up. */ |
| per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; |
| return rcu_needs_cpu_quick_check(cpu); |
| } |
| |
| /* Do one step pushing remaining RCU callbacks through. */ |
| if (per_cpu(rcu_sched_data, cpu).nxtlist) { |
| rcu_sched_qs(cpu); |
| force_quiescent_state(&rcu_sched_state, 0); |
| c = c || per_cpu(rcu_sched_data, cpu).nxtlist; |
| } |
| if (per_cpu(rcu_bh_data, cpu).nxtlist) { |
| rcu_bh_qs(cpu); |
| force_quiescent_state(&rcu_bh_state, 0); |
| c = c || per_cpu(rcu_bh_data, cpu).nxtlist; |
| } |
| |
| /* If RCU callbacks are still pending, RCU still needs this CPU. */ |
| if (c) |
| invoke_rcu_cpu_kthread(); |
| return c; |
| } |
| |
| /* |
| * Check to see if we need to continue a callback-flush operations to |
| * allow the last CPU to enter dyntick-idle mode. |
| */ |
| static void rcu_needs_cpu_flush(void) |
| { |
| int cpu = smp_processor_id(); |
| unsigned long flags; |
| |
| if (per_cpu(rcu_dyntick_drain, cpu) <= 0) |
| return; |
| local_irq_save(flags); |
| (void)rcu_needs_cpu(cpu); |
| local_irq_restore(flags); |
| } |
| |
| #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |