/* * 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, you can access it online at * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright Red Hat, 2009 * Copyright IBM Corporation, 2009 * * Author: Ingo Molnar * Paul E. McKenney */ #include #include #include #include #include "../time/tick-internal.h" #define RCU_KTHREAD_PRIO 1 #ifdef CONFIG_RCU_BOOST #include "../locking/rtmutex_common.h" #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 pr_info("\tRCU debugfs-based tracing is enabled.\n"); #endif #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", CONFIG_RCU_FANOUT); #endif #ifdef CONFIG_RCU_FANOUT_EXACT pr_info("\tHierarchical RCU autobalancing is disabled.\n"); #endif #ifdef CONFIG_RCU_FAST_NO_HZ pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); #endif #ifdef CONFIG_PROVE_RCU pr_info("\tRCU lockdep checking is enabled.\n"); #endif #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE pr_info("\tRCU torture testing starts during boot.\n"); #endif #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n"); #endif #if defined(CONFIG_RCU_CPU_STALL_INFO) pr_info("\tAdditional per-CPU info printed with stalls.\n"); #endif #if NUM_RCU_LVL_4 != 0 pr_info("\tFour-level hierarchy is enabled.\n"); #endif if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); if (nr_cpu_ids != NR_CPUS) pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); } #ifdef CONFIG_TREE_PREEMPT_RCU RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); static struct rcu_state *rcu_state_p = &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) { pr_info("Preemptible hierarchical RCU implementation.\n"); rcu_bootup_announce_oddness(); } /* * Return the number of RCU-preempt batches processed thus far * for debug and statistics. */ static 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); /* * 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. * * As with the other rcu_*_qs() functions, callers to this function * must disable preemption. */ static void rcu_preempt_qs(void) { if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) { trace_rcu_grace_period(TPS("rcu_preempt"), __this_cpu_read(rcu_preempt_data.gpnum), TPS("cpuqs")); __this_cpu_write(rcu_preempt_data.passed_quiesce, 1); barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */ current->rcu_read_unlock_special.b.need_qs = false; } } /* * 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.b.blocked) { /* 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); smp_mb__after_unlock_lock(); t->rcu_read_unlock_special.b.blocked = true; 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.s) { /* * 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. */ rcu_preempt_qs(); } /* * 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. */ smp_mb__after_unlock_lock(); 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 bool drop_boost_mutex = false; #endif /* #ifdef CONFIG_RCU_BOOST */ struct rcu_node *rnp; union rcu_special 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. Because irqs are disabled, * t->rcu_read_unlock_special cannot change. */ special = t->rcu_read_unlock_special; if (special.b.need_qs) { rcu_preempt_qs(); if (!t->rcu_read_unlock_special.s) { local_irq_restore(flags); return; } } /* Hardware IRQ handlers cannot block, complain if they get here. */ if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) { local_irq_restore(flags); return; } /* Clean up if blocked during RCU read-side critical section. */ if (special.b.blocked) { t->rcu_read_unlock_special.b.blocked = false; /* * 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. */ smp_mb__after_unlock_lock(); 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(TPS("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 ->boost_mtx ownership with rcu_node lock held. */ drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t; #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(TPS("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 (drop_boost_mutex) { rt_mutex_unlock(&rnp->boost_mtx); complete(&rnp->boost_completion); } #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) { pr_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) { pr_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) { pr_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 */ smp_mb__after_unlock_lock(); 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 */ smp_mb__after_unlock_lock(); 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(); return; } if (t->rcu_read_lock_nesting > 0 && per_cpu(rcu_preempt_data, cpu).qs_pending && !per_cpu(rcu_preempt_data, cpu).passed_quiesce) t->rcu_read_unlock_special.b.need_qs = true; } #ifdef CONFIG_RCU_BOOST static void rcu_preempt_do_callbacks(void) { rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&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); /** * 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); smp_mb__after_unlock_lock(); 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) { smp_mb(); /* EGP done before wake_up(). */ 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 */ smp_mb__after_unlock_lock(); 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); smp_mb__after_unlock_lock(); 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. */ 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. */ if (!try_get_online_cpus()) { /* CPU-hotplug operation in flight, fall back to normal GP. */ wait_rcu_gp(call_rcu); return; } /* * 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); smp_mb__after_unlock_lock(); 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) = sync_rcu_preempt_exp_count + 1; 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); } /* * 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 (likely(list_empty(¤t->rcu_node_entry))) return; t->rcu_read_lock_nesting = 1; barrier(); t->rcu_read_unlock_special.b.blocked = true; __rcu_read_unlock(); } #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ static struct rcu_state *rcu_state_p = &rcu_sched_state; /* * Tell them what RCU they are running. */ static void __init rcu_bootup_announce(void) { pr_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); /* * 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) __releases(rnp->lock) { 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) { } /* * 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) { } /* * Because preemptible RCU does not exist, tasks cannot possibly exit * while in preemptible RCU read-side critical sections. */ void exit_rcu(void) { } #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ #ifdef CONFIG_RCU_BOOST #include "../locking/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 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); smp_mb__after_unlock_lock(); /* * 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(&rnp->boost_mtx, t); init_completion(&rnp->boost_completion); raw_spin_unlock_irqrestore(&rnp->lock, flags); /* Lock only for side effect: boosts task t's priority. */ rt_mutex_lock(&rnp->boost_mtx); rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ /* Wait for boostee to be done w/boost_mtx before reinitializing. */ wait_for_completion(&rnp->boost_completion); 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(TPS("Start boost kthread@init")); for (;;) { rnp->boost_kthread_status = RCU_KTHREAD_WAITING; trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); rcu_wait(rnp->boost_tasks || rnp->exp_tasks); trace_rcu_utilization(TPS("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(TPS("End boost kthread@rcu_yield")); schedule_timeout_interruptible(2); trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); spincnt = 0; } } /* NOTREACHED */ trace_rcu_utilization(TPS("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) __releases(rnp->lock) { 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 __this_cpu_read(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 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); smp_mb__after_unlock_lock(); 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, this_cpu_ptr(&rcu_sched_data)); rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&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 __this_cpu_read(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 = this_cpu_ptr(&rcu_cpu_kthread_status); char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); int spincnt; for (spincnt = 0; spincnt < 10; spincnt++) { trace_rcu_utilization(TPS("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(TPS("End CPU kthread@rcu_wait")); *statusp = RCU_KTHREAD_WAITING; return; } } *statusp = RCU_KTHREAD_YIELDING; trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); schedule_timeout_interruptible(2); trace_rcu_utilization(TPS("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 boost kthreads -- called as soon as the scheduler is running. */ static void __init rcu_spawn_boost_kthreads(void) { struct rcu_node *rnp; int cpu; 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_p); (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); if (NUM_RCU_NODES > 1) { rcu_for_each_leaf_node(rcu_state_p, rnp) (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); } } static void rcu_prepare_kthreads(int cpu) { struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->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_p, rnp); } #else /* #ifdef CONFIG_RCU_BOOST */ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { 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 void __init rcu_spawn_boost_kthreads(void) { } static void 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. */ #ifndef CONFIG_RCU_NOCB_CPU_ALL int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) { *delta_jiffies = ULONG_MAX; return rcu_cpu_has_callbacks(cpu, NULL); } #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ /* * 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_active; /* * Try to advance callbacks for all flavors of RCU on the current CPU, but * only if it has been awhile since the last time we did so. Afterwards, * if there are any callbacks ready for immediate invocation, return true. */ static bool __maybe_unused rcu_try_advance_all_cbs(void) { bool cbs_ready = false; struct rcu_data *rdp; struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); struct rcu_node *rnp; struct rcu_state *rsp; /* Exit early if we advanced recently. */ if (jiffies == rdtp->last_advance_all) return false; rdtp->last_advance_all = jiffies; 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]) note_gp_changes(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. */ #ifndef CONFIG_RCU_NOCB_CPU_ALL 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; } #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ /* * 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) { #ifndef CONFIG_RCU_NOCB_CPU_ALL bool needwake; 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_active); 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) { rdtp->all_lazy = false; rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 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. */ smp_mb__after_unlock_lock(); needwake = rcu_accelerate_cbs(rsp, rnp, rdp); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ if (needwake) rcu_gp_kthread_wake(rsp); } #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ } /* * 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) { #ifndef CONFIG_RCU_NOCB_CPU_ALL if (rcu_is_nocb_cpu(cpu)) return; if (rcu_try_advance_all_cbs()) invoke_rcu_core(); #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ } /* * 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 = raw_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); smp_mb(); /* Ensure callback reuse happens after callback invocation. */ /* * 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_rcu_qs(); } 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) { pr_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); pr_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) { pr_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) raw_cpu_inc(rsp->rda->ticks_this_gp); } #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ static void print_cpu_stall_info_begin(void) { pr_cont(" {"); } static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) { pr_cont(" %d", cpu); } static void print_cpu_stall_info_end(void) { pr_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); /* * 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]); } #ifndef CONFIG_RCU_NOCB_CPU_ALL /* Is the specified CPU a no-CBs CPU? */ bool rcu_is_nocb_cpu(int cpu) { if (have_rcu_nocb_mask) return cpumask_test_cpu(cpu, rcu_nocb_mask); return false; } #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ /* * Kick the leader kthread for this NOCB group. */ static void wake_nocb_leader(struct rcu_data *rdp, bool force) { struct rcu_data *rdp_leader = rdp->nocb_leader; if (!ACCESS_ONCE(rdp_leader->nocb_kthread)) return; if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) { /* Prior smp_mb__after_atomic() orders against prior enqueue. */ ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false; wake_up(&rdp_leader->nocb_wq); } } /* * Does the specified CPU need an RCU callback for the specified flavor * of rcu_barrier()? */ static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) { struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_head *rhp; /* No-CBs CPUs might have callbacks on any of three lists. */ rhp = ACCESS_ONCE(rdp->nocb_head); if (!rhp) rhp = ACCESS_ONCE(rdp->nocb_gp_head); if (!rhp) rhp = ACCESS_ONCE(rdp->nocb_follower_head); /* Having no rcuo kthread but CBs after scheduler starts is bad! */ if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) { /* RCU callback enqueued before CPU first came online??? */ pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", cpu, rhp->func); WARN_ON_ONCE(1); } return !!rhp; } /* * 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, unsigned long flags) { 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); smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ /* If we are not being polled and there is a kthread, awaken it ... */ t = ACCESS_ONCE(rdp->nocb_kthread); if (rcu_nocb_poll || !t) { trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNotPoll")); return; } len = atomic_long_read(&rdp->nocb_q_count); if (old_rhpp == &rdp->nocb_head) { if (!irqs_disabled_flags(flags)) { /* ... if queue was empty ... */ wake_nocb_leader(rdp, false); trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmpty")); } else { rdp->nocb_defer_wakeup = RCU_NOGP_WAKE; trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmptyIsDeferred")); } rdp->qlen_last_fqs_check = 0; } else if (len > rdp->qlen_last_fqs_check + qhimark) { /* ... or if many callbacks queued. */ if (!irqs_disabled_flags(flags)) { wake_nocb_leader(rdp, true); trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf")); } else { rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE; trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvfIsDeferred")); } rdp->qlen_last_fqs_check = LONG_MAX / 2; } else { trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); } 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, unsigned long flags) { if (!rcu_is_nocb_cpu(rdp->cpu)) return false; __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); if (__is_kfree_rcu_offset((unsigned long)rhp->func)) trace_rcu_kfree_callback(rdp->rsp->name, rhp, (unsigned long)rhp->func, -atomic_long_read(&rdp->nocb_q_count_lazy), -atomic_long_read(&rdp->nocb_q_count)); else trace_rcu_callback(rdp->rsp->name, rhp, -atomic_long_read(&rdp->nocb_q_count_lazy), -atomic_long_read(&rdp->nocb_q_count)); /* * If called from an extended quiescent state with interrupts * disabled, invoke the RCU core in order to allow the idle-entry * deferred-wakeup check to function. */ if (irqs_disabled_flags(flags) && !rcu_is_watching() && cpu_online(smp_processor_id())) invoke_rcu_core(); return true; } /* * 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, unsigned long flags) { 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 false; 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, flags); 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, flags); ql = qll = 0; rsp->orphan_nxtlist = NULL; rsp->orphan_nxttail = &rsp->orphan_nxtlist; } return true; } /* * 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; bool needwake; struct rcu_node *rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); smp_mb__after_unlock_lock(); needwake = rcu_start_future_gp(rnp, rdp, &c); raw_spin_unlock_irqrestore(&rnp->lock, flags); if (needwake) rcu_gp_kthread_wake(rdp->rsp); /* * Wait for the grace period. Do so interruptibly to avoid messing * up the load average. */ trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); for (;;) { wait_event_interruptible( rnp->nocb_gp_wq[c & 0x1], (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c))); if (likely(d)) break; WARN_ON(signal_pending(current)); trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); } trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); smp_mb(); /* Ensure that CB invocation happens after GP end. */ } /* * Leaders come here to wait for additional callbacks to show up. * This function does not return until callbacks appear. */ static void nocb_leader_wait(struct rcu_data *my_rdp) { bool firsttime = true; bool gotcbs; struct rcu_data *rdp; struct rcu_head **tail; wait_again: /* Wait for callbacks to appear. */ if (!rcu_nocb_poll) { trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep"); wait_event_interruptible(my_rdp->nocb_wq, !ACCESS_ONCE(my_rdp->nocb_leader_sleep)); /* Memory barrier handled by smp_mb() calls below and repoll. */ } else if (firsttime) { firsttime = false; /* Don't drown trace log with "Poll"! */ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll"); } /* * Each pass through the following loop checks a follower for CBs. * We are our own first follower. Any CBs found are moved to * nocb_gp_head, where they await a grace period. */ gotcbs = false; for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { rdp->nocb_gp_head = ACCESS_ONCE(rdp->nocb_head); if (!rdp->nocb_gp_head) continue; /* No CBs here, try next follower. */ /* Move callbacks to wait-for-GP list, which is empty. */ ACCESS_ONCE(rdp->nocb_head) = NULL; rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); rdp->nocb_gp_count = atomic_long_xchg(&rdp->nocb_q_count, 0); rdp->nocb_gp_count_lazy = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); gotcbs = true; } /* * If there were no callbacks, sleep a bit, rescan after a * memory barrier, and go retry. */ if (unlikely(!gotcbs)) { if (!rcu_nocb_poll) trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "WokeEmpty"); WARN_ON(signal_pending(current)); schedule_timeout_interruptible(1); /* Rescan in case we were a victim of memory ordering. */ my_rdp->nocb_leader_sleep = true; smp_mb(); /* Ensure _sleep true before scan. */ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) if (ACCESS_ONCE(rdp->nocb_head)) { /* Found CB, so short-circuit next wait. */ my_rdp->nocb_leader_sleep = false; break; } goto wait_again; } /* Wait for one grace period. */ rcu_nocb_wait_gp(my_rdp); /* * We left ->nocb_leader_sleep unset to reduce cache thrashing. * We set it now, but recheck for new callbacks while * traversing our follower list. */ my_rdp->nocb_leader_sleep = true; smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */ /* Each pass through the following loop wakes a follower, if needed. */ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { if (ACCESS_ONCE(rdp->nocb_head)) my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ if (!rdp->nocb_gp_head) continue; /* No CBs, so no need to wake follower. */ /* Append callbacks to follower's "done" list. */ tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail); *tail = rdp->nocb_gp_head; atomic_long_add(rdp->nocb_gp_count, &rdp->nocb_follower_count); atomic_long_add(rdp->nocb_gp_count_lazy, &rdp->nocb_follower_count_lazy); smp_mb__after_atomic(); /* Store *tail before wakeup. */ if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { /* * List was empty, wake up the follower. * Memory barriers supplied by atomic_long_add(). */ wake_up(&rdp->nocb_wq); } } /* If we (the leader) don't have CBs, go wait some more. */ if (!my_rdp->nocb_follower_head) goto wait_again; } /* * Followers come here to wait for additional callbacks to show up. * This function does not return until callbacks appear. */ static void nocb_follower_wait(struct rcu_data *rdp) { bool firsttime = true; for (;;) { if (!rcu_nocb_poll) { trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "FollowerSleep"); wait_event_interruptible(rdp->nocb_wq, ACCESS_ONCE(rdp->nocb_follower_head)); } else if (firsttime) { /* Don't drown trace log with "Poll"! */ firsttime = false; trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll"); } if (smp_load_acquire(&rdp->nocb_follower_head)) { /* ^^^ Ensure CB invocation follows _head test. */ return; } if (!rcu_nocb_poll) trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeEmpty"); WARN_ON(signal_pending(current)); schedule_timeout_interruptible(1); } } /* * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes * callbacks queued by the corresponding no-CBs CPU, however, there is * an optional leader-follower relationship so that the grace-period * kthreads don't have to do quite so many wakeups. */ 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 (;;) { /* Wait for callbacks. */ if (rdp->nocb_leader == rdp) nocb_leader_wait(rdp); else nocb_follower_wait(rdp); /* Pull the ready-to-invoke callbacks onto local list. */ list = ACCESS_ONCE(rdp->nocb_follower_head); BUG_ON(!list); trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty"); ACCESS_ONCE(rdp->nocb_follower_head) = NULL; tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head); c = atomic_long_xchg(&rdp->nocb_follower_count, 0); cl = atomic_long_xchg(&rdp->nocb_follower_count_lazy, 0); rdp->nocb_p_count += c; rdp->nocb_p_count_lazy += cl; /* 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) { trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WaitQueue")); schedule_timeout_interruptible(1); trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeQueue")); 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) = rdp->nocb_p_count - c; ACCESS_ONCE(rdp->nocb_p_count_lazy) = rdp->nocb_p_count_lazy - cl; rdp->n_nocbs_invoked += c; } return 0; } /* Is a deferred wakeup of rcu_nocb_kthread() required? */ static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) { return ACCESS_ONCE(rdp->nocb_defer_wakeup); } /* Do a deferred wakeup of rcu_nocb_kthread(). */ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) { int ndw; if (!rcu_nocb_need_deferred_wakeup(rdp)) return; ndw = ACCESS_ONCE(rdp->nocb_defer_wakeup); ACCESS_ONCE(rdp->nocb_defer_wakeup) = RCU_NOGP_WAKE_NOT; wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE); trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake")); } void __init rcu_init_nohz(void) { int cpu; bool need_rcu_nocb_mask = true; struct rcu_state *rsp; #ifdef CONFIG_RCU_NOCB_CPU_NONE need_rcu_nocb_mask = false; #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ #if defined(CONFIG_NO_HZ_FULL) if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) need_rcu_nocb_mask = true; #endif /* #if defined(CONFIG_NO_HZ_FULL) */ if (!have_rcu_nocb_mask && need_rcu_nocb_mask) { if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); return; } have_rcu_nocb_mask = true; } if (!have_rcu_nocb_mask) return; #ifdef CONFIG_RCU_NOCB_CPU_ZERO pr_info("\tOffload RCU callbacks from 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("\tOffload RCU callbacks from all CPUs\n"); cpumask_copy(rcu_nocb_mask, cpu_possible_mask); #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ #if defined(CONFIG_NO_HZ_FULL) if (tick_nohz_full_running) cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); #endif /* #if defined(CONFIG_NO_HZ_FULL) */ if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); cpumask_and(rcu_nocb_mask, cpu_possible_mask, rcu_nocb_mask); } cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf); if (rcu_nocb_poll) pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); for_each_rcu_flavor(rsp) { for_each_cpu(cpu, rcu_nocb_mask) { struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); /* * If there are early callbacks, they will need * to be moved to the nocb lists. */ WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] != &rdp->nxtlist && rdp->nxttail[RCU_NEXT_TAIL] != NULL); init_nocb_callback_list(rdp); } rcu_organize_nocb_kthreads(rsp); } } /* 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); rdp->nocb_follower_tail = &rdp->nocb_follower_head; } /* * If the specified CPU is a no-CBs CPU that does not already have its * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are * brought online out of order, this can require re-organizing the * leader-follower relationships. */ static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu) { struct rcu_data *rdp; struct rcu_data *rdp_last; struct rcu_data *rdp_old_leader; struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu); struct task_struct *t; /* * If this isn't a no-CBs CPU or if it already has an rcuo kthread, * then nothing to do. */ if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) return; /* If we didn't spawn the leader first, reorganize! */ rdp_old_leader = rdp_spawn->nocb_leader; if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { rdp_last = NULL; rdp = rdp_old_leader; do { rdp->nocb_leader = rdp_spawn; if (rdp_last && rdp != rdp_spawn) rdp_last->nocb_next_follower = rdp; rdp_last = rdp; rdp = rdp->nocb_next_follower; rdp_last->nocb_next_follower = NULL; } while (rdp); rdp_spawn->nocb_next_follower = rdp_old_leader; } /* Spawn the kthread for this CPU and RCU flavor. */ t = kthread_run(rcu_nocb_kthread, rdp_spawn, "rcuo%c/%d", rsp->abbr, cpu); BUG_ON(IS_ERR(t)); ACCESS_ONCE(rdp_spawn->nocb_kthread) = t; } /* * If the specified CPU is a no-CBs CPU that does not already have its * rcuo kthreads, spawn them. */ static void rcu_spawn_all_nocb_kthreads(int cpu) { struct rcu_state *rsp; if (rcu_scheduler_fully_active) for_each_rcu_flavor(rsp) rcu_spawn_one_nocb_kthread(rsp, cpu); } /* * Once the scheduler is running, spawn rcuo kthreads for all online * no-CBs CPUs. This assumes that the early_initcall()s happen before * non-boot CPUs come online -- if this changes, we will need to add * some mutual exclusion. */ static void __init rcu_spawn_nocb_kthreads(void) { int cpu; for_each_online_cpu(cpu) rcu_spawn_all_nocb_kthreads(cpu); } /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ static int rcu_nocb_leader_stride = -1; module_param(rcu_nocb_leader_stride, int, 0444); /* * Initialize leader-follower relationships for all no-CBs CPU. */ static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp) { int cpu; int ls = rcu_nocb_leader_stride; int nl = 0; /* Next leader. */ struct rcu_data *rdp; struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ struct rcu_data *rdp_prev = NULL; if (!have_rcu_nocb_mask) return; if (ls == -1) { ls = int_sqrt(nr_cpu_ids); rcu_nocb_leader_stride = ls; } /* * Each pass through this loop sets up one rcu_data structure and * spawns one rcu_nocb_kthread(). */ for_each_cpu(cpu, rcu_nocb_mask) { rdp = per_cpu_ptr(rsp->rda, cpu); if (rdp->cpu >= nl) { /* New leader, set up for followers & next leader. */ nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; rdp->nocb_leader = rdp; rdp_leader = rdp; } else { /* Another follower, link to previous leader. */ rdp->nocb_leader = rdp_leader; rdp_prev->nocb_next_follower = rdp; } rdp_prev = rdp; } } /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ static bool init_nocb_callback_list(struct rcu_data *rdp) { if (!rcu_is_nocb_cpu(rdp->cpu)) return false; rdp->nxttail[RCU_NEXT_TAIL] = NULL; return true; } #else /* #ifdef CONFIG_RCU_NOCB_CPU */ static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) { WARN_ON_ONCE(1); /* Should be dead code. */ return false; } 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, unsigned long flags) { return false; } static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, struct rcu_data *rdp, unsigned long flags) { return false; } static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) { } static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) { return false; } static void do_nocb_deferred_wakeup(struct rcu_data *rdp) { } static void rcu_spawn_all_nocb_kthreads(int cpu) { } static void __init rcu_spawn_nocb_kthreads(void) { } 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 __maybe_unused 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 */ } #ifdef CONFIG_NO_HZ_FULL_SYSIDLE static int full_sysidle_state; /* Current system-idle state. */ #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ /* * Invoked to note exit from irq or task transition to idle. Note that * usermode execution does -not- count as idle here! After all, we want * to detect full-system idle states, not RCU quiescent states and grace * periods. The caller must have disabled interrupts. */ static void rcu_sysidle_enter(int irq) { unsigned long j; struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); /* If there are no nohz_full= CPUs, no need to track this. */ if (!tick_nohz_full_enabled()) return; /* Adjust nesting, check for fully idle. */ if (irq) { rdtp->dynticks_idle_nesting--; WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); if (rdtp->dynticks_idle_nesting != 0) return; /* Still not fully idle. */ } else { if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) { rdtp->dynticks_idle_nesting = 0; } else { rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); return; /* Still not fully idle. */ } } /* Record start of fully idle period. */ j = jiffies; ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j; smp_mb__before_atomic(); atomic_inc(&rdtp->dynticks_idle); smp_mb__after_atomic(); WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); } /* * Unconditionally force exit from full system-idle state. This is * invoked when a normal CPU exits idle, but must be called separately * for the timekeeping CPU (tick_do_timer_cpu). The reason for this * is that the timekeeping CPU is permitted to take scheduling-clock * interrupts while the system is in system-idle state, and of course * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock * interrupt from any other type of interrupt. */ void rcu_sysidle_force_exit(void) { int oldstate = ACCESS_ONCE(full_sysidle_state); int newoldstate; /* * Each pass through the following loop attempts to exit full * system-idle state. If contention proves to be a problem, * a trylock-based contention tree could be used here. */ while (oldstate > RCU_SYSIDLE_SHORT) { newoldstate = cmpxchg(&full_sysidle_state, oldstate, RCU_SYSIDLE_NOT); if (oldstate == newoldstate && oldstate == RCU_SYSIDLE_FULL_NOTED) { rcu_kick_nohz_cpu(tick_do_timer_cpu); return; /* We cleared it, done! */ } oldstate = newoldstate; } smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ } /* * Invoked to note entry to irq or task transition from idle. Note that * usermode execution does -not- count as idle here! The caller must * have disabled interrupts. */ static void rcu_sysidle_exit(int irq) { struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); /* If there are no nohz_full= CPUs, no need to track this. */ if (!tick_nohz_full_enabled()) return; /* Adjust nesting, check for already non-idle. */ if (irq) { rdtp->dynticks_idle_nesting++; WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); if (rdtp->dynticks_idle_nesting != 1) return; /* Already non-idle. */ } else { /* * Allow for irq misnesting. Yes, it really is possible * to enter an irq handler then never leave it, and maybe * also vice versa. Handle both possibilities. */ if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); return; /* Already non-idle. */ } else { rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; } } /* Record end of idle period. */ smp_mb__before_atomic(); atomic_inc(&rdtp->dynticks_idle); smp_mb__after_atomic(); WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); /* * If we are the timekeeping CPU, we are permitted to be non-idle * during a system-idle state. This must be the case, because * the timekeeping CPU has to take scheduling-clock interrupts * during the time that the system is transitioning to full * system-idle state. This means that the timekeeping CPU must * invoke rcu_sysidle_force_exit() directly if it does anything * more than take a scheduling-clock interrupt. */ if (smp_processor_id() == tick_do_timer_cpu) return; /* Update system-idle state: We are clearly no longer fully idle! */ rcu_sysidle_force_exit(); } /* * Check to see if the current CPU is idle. Note that usermode execution * does not count as idle. The caller must have disabled interrupts. */ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, unsigned long *maxj) { int cur; unsigned long j; struct rcu_dynticks *rdtp = rdp->dynticks; /* If there are no nohz_full= CPUs, don't check system-wide idleness. */ if (!tick_nohz_full_enabled()) return; /* * If some other CPU has already reported non-idle, if this is * not the flavor of RCU that tracks sysidle state, or if this * is an offline or the timekeeping CPU, nothing to do. */ if (!*isidle || rdp->rsp != rcu_state_p || cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) return; if (rcu_gp_in_progress(rdp->rsp)) WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); /* Pick up current idle and NMI-nesting counter and check. */ cur = atomic_read(&rdtp->dynticks_idle); if (cur & 0x1) { *isidle = false; /* We are not idle! */ return; } smp_mb(); /* Read counters before timestamps. */ /* Pick up timestamps. */ j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies); /* If this CPU entered idle more recently, update maxj timestamp. */ if (ULONG_CMP_LT(*maxj, j)) *maxj = j; } /* * Is this the flavor of RCU that is handling full-system idle? */ static bool is_sysidle_rcu_state(struct rcu_state *rsp) { return rsp == rcu_state_p; } /* * Return a delay in jiffies based on the number of CPUs, rcu_node * leaf fanout, and jiffies tick rate. The idea is to allow larger * systems more time to transition to full-idle state in order to * avoid the cache thrashing that otherwise occur on the state variable. * Really small systems (less than a couple of tens of CPUs) should * instead use a single global atomically incremented counter, and later * versions of this will automatically reconfigure themselves accordingly. */ static unsigned long rcu_sysidle_delay(void) { if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) return 0; return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); } /* * Advance the full-system-idle state. This is invoked when all of * the non-timekeeping CPUs are idle. */ static void rcu_sysidle(unsigned long j) { /* Check the current state. */ switch (ACCESS_ONCE(full_sysidle_state)) { case RCU_SYSIDLE_NOT: /* First time all are idle, so note a short idle period. */ ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT; break; case RCU_SYSIDLE_SHORT: /* * Idle for a bit, time to advance to next state? * cmpxchg failure means race with non-idle, let them win. */ if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) (void)cmpxchg(&full_sysidle_state, RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); break; case RCU_SYSIDLE_LONG: /* * Do an additional check pass before advancing to full. * cmpxchg failure means race with non-idle, let them win. */ if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) (void)cmpxchg(&full_sysidle_state, RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); break; default: break; } } /* * Found a non-idle non-timekeeping CPU, so kick the system-idle state * back to the beginning. */ static void rcu_sysidle_cancel(void) { smp_mb(); if (full_sysidle_state > RCU_SYSIDLE_SHORT) ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT; } /* * Update the sysidle state based on the results of a force-quiescent-state * scan of the CPUs' dyntick-idle state. */ static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, unsigned long maxj, bool gpkt) { if (rsp != rcu_state_p) return; /* Wrong flavor, ignore. */ if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) return; /* Running state machine from timekeeping CPU. */ if (isidle) rcu_sysidle(maxj); /* More idle! */ else rcu_sysidle_cancel(); /* Idle is over. */ } /* * Wrapper for rcu_sysidle_report() when called from the grace-period * kthread's context. */ static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, unsigned long maxj) { /* If there are no nohz_full= CPUs, no need to track this. */ if (!tick_nohz_full_enabled()) return; rcu_sysidle_report(rsp, isidle, maxj, true); } /* Callback and function for forcing an RCU grace period. */ struct rcu_sysidle_head { struct rcu_head rh; int inuse; }; static void rcu_sysidle_cb(struct rcu_head *rhp) { struct rcu_sysidle_head *rshp; /* * The following memory barrier is needed to replace the * memory barriers that would normally be in the memory * allocator. */ smp_mb(); /* grace period precedes setting inuse. */ rshp = container_of(rhp, struct rcu_sysidle_head, rh); ACCESS_ONCE(rshp->inuse) = 0; } /* * Check to see if the system is fully idle, other than the timekeeping CPU. * The caller must have disabled interrupts. This is not intended to be * called unless tick_nohz_full_enabled(). */ bool rcu_sys_is_idle(void) { static struct rcu_sysidle_head rsh; int rss = ACCESS_ONCE(full_sysidle_state); if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) return false; /* Handle small-system case by doing a full scan of CPUs. */ if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { int oldrss = rss - 1; /* * One pass to advance to each state up to _FULL. * Give up if any pass fails to advance the state. */ while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { int cpu; bool isidle = true; unsigned long maxj = jiffies - ULONG_MAX / 4; struct rcu_data *rdp; /* Scan all the CPUs looking for nonidle CPUs. */ for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(rcu_state_p->rda, cpu); rcu_sysidle_check_cpu(rdp, &isidle, &maxj); if (!isidle) break; } rcu_sysidle_report(rcu_state_p, isidle, maxj, false); oldrss = rss; rss = ACCESS_ONCE(full_sysidle_state); } } /* If this is the first observation of an idle period, record it. */ if (rss == RCU_SYSIDLE_FULL) { rss = cmpxchg(&full_sysidle_state, RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); return rss == RCU_SYSIDLE_FULL; } smp_mb(); /* ensure rss load happens before later caller actions. */ /* If already fully idle, tell the caller (in case of races). */ if (rss == RCU_SYSIDLE_FULL_NOTED) return true; /* * If we aren't there yet, and a grace period is not in flight, * initiate a grace period. Either way, tell the caller that * we are not there yet. We use an xchg() rather than an assignment * to make up for the memory barriers that would otherwise be * provided by the memory allocator. */ if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && !rcu_gp_in_progress(rcu_state_p) && !rsh.inuse && xchg(&rsh.inuse, 1) == 0) call_rcu(&rsh.rh, rcu_sysidle_cb); return false; } /* * Initialize dynticks sysidle state for CPUs coming online. */ static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) { rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; } #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ static void rcu_sysidle_enter(int irq) { } static void rcu_sysidle_exit(int irq) { } static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, unsigned long *maxj) { } static bool is_sysidle_rcu_state(struct rcu_state *rsp) { return false; } static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, unsigned long maxj) { } static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) { } #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ /* * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the * grace-period kthread will do force_quiescent_state() processing? * The idea is to avoid waking up RCU core processing on such a * CPU unless the grace period has extended for too long. * * This code relies on the fact that all NO_HZ_FULL CPUs are also * CONFIG_RCU_NOCB_CPU CPUs. */ static bool rcu_nohz_full_cpu(struct rcu_state *rsp) { #ifdef CONFIG_NO_HZ_FULL if (tick_nohz_full_cpu(smp_processor_id()) && (!rcu_gp_in_progress(rsp) || ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ))) return 1; #endif /* #ifdef CONFIG_NO_HZ_FULL */ return 0; } /* * Bind the grace-period kthread for the sysidle flavor of RCU to the * timekeeping CPU. */ static void rcu_bind_gp_kthread(void) { int __maybe_unused cpu; if (!tick_nohz_full_enabled()) return; #ifdef CONFIG_NO_HZ_FULL_SYSIDLE cpu = tick_do_timer_cpu; if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu) set_cpus_allowed_ptr(current, cpumask_of(cpu)); #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ if (!is_housekeeping_cpu(raw_smp_processor_id())) housekeeping_affine(current); #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ } /* Record the current task on dyntick-idle entry. */ static void rcu_dynticks_task_enter(void) { #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id(); #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ } /* Record no current task on dyntick-idle exit. */ static void rcu_dynticks_task_exit(void) { #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1; #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ }