/* * Read-Copy Update mechanism for mutual exclusion * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright IBM Corporation, 2008 * * Authors: Dipankar Sarma * Manfred Spraul * Paul E. McKenney Hierarchical version * * Based on the original work by Paul McKenney * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * * For detailed explanation of Read-Copy Update mechanism see - * Documentation/RCU */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "rcutree.h" #include #include "rcu.h" /* Data structures. */ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; #define RCU_STATE_INITIALIZER(sname, cr) { \ .level = { &sname##_state.node[0] }, \ .call = cr, \ .fqs_state = RCU_GP_IDLE, \ .gpnum = -300, \ .completed = -300, \ .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.onofflock), \ .orphan_nxttail = &sname##_state.orphan_nxtlist, \ .orphan_donetail = &sname##_state.orphan_donelist, \ .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.fqslock), \ .name = #sname, \ } struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, call_rcu_bh); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); static struct rcu_state *rcu_state; LIST_HEAD(rcu_struct_flavors); /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */ static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF; module_param(rcu_fanout_leaf, int, 0); int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */ NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3, NUM_RCU_LVL_4, }; int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ /* * The rcu_scheduler_active variable transitions from zero to one just * before the first task is spawned. So when this variable is zero, RCU * can assume that there is but one task, allowing RCU to (for example) * optimized synchronize_sched() to a simple barrier(). When this variable * is one, RCU must actually do all the hard work required to detect real * grace periods. This variable is also used to suppress boot-time false * positives from lockdep-RCU error checking. */ int rcu_scheduler_active __read_mostly; EXPORT_SYMBOL_GPL(rcu_scheduler_active); /* * The rcu_scheduler_fully_active variable transitions from zero to one * during the early_initcall() processing, which is after the scheduler * is capable of creating new tasks. So RCU processing (for example, * creating tasks for RCU priority boosting) must be delayed until after * rcu_scheduler_fully_active transitions from zero to one. We also * currently delay invocation of any RCU callbacks until after this point. * * It might later prove better for people registering RCU callbacks during * early boot to take responsibility for these callbacks, but one step at * a time. */ static int rcu_scheduler_fully_active __read_mostly; #ifdef CONFIG_RCU_BOOST /* * Control variables for per-CPU and per-rcu_node kthreads. These * handle all flavors of RCU. */ static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu); DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); DEFINE_PER_CPU(char, rcu_cpu_has_work); #endif /* #ifdef CONFIG_RCU_BOOST */ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); static void invoke_rcu_core(void); static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); /* * Track the rcutorture test sequence number and the update version * number within a given test. The rcutorture_testseq is incremented * on every rcutorture module load and unload, so has an odd value * when a test is running. The rcutorture_vernum is set to zero * when rcutorture starts and is incremented on each rcutorture update. * These variables enable correlating rcutorture output with the * RCU tracing information. */ unsigned long rcutorture_testseq; unsigned long rcutorture_vernum; /* * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s * permit this function to be invoked without holding the root rcu_node * structure's ->lock, but of course results can be subject to change. */ static int rcu_gp_in_progress(struct rcu_state *rsp) { return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum); } /* * Note a quiescent state. Because we do not need to know * how many quiescent states passed, just if there was at least * one since the start of the grace period, this just sets a flag. * The caller must have disabled preemption. */ void rcu_sched_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu); rdp->passed_quiesce_gpnum = rdp->gpnum; barrier(); if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; } void rcu_bh_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); rdp->passed_quiesce_gpnum = rdp->gpnum; barrier(); if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; } /* * Note a context switch. This is a quiescent state for RCU-sched, * and requires special handling for preemptible RCU. * The caller must have disabled preemption. */ void rcu_note_context_switch(int cpu) { trace_rcu_utilization("Start context switch"); rcu_sched_qs(cpu); rcu_preempt_note_context_switch(cpu); trace_rcu_utilization("End context switch"); } EXPORT_SYMBOL_GPL(rcu_note_context_switch); DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE, .dynticks = ATOMIC_INIT(1), }; static int blimit = 10; /* Maximum callbacks per rcu_do_batch. */ static int qhimark = 10000; /* If this many pending, ignore blimit. */ static int qlowmark = 100; /* Once only this many pending, use blimit. */ module_param(blimit, int, 0); module_param(qhimark, int, 0); module_param(qlowmark, int, 0); int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_suppress, int, 0644); module_param(rcu_cpu_stall_timeout, int, 0644); static void force_quiescent_state(struct rcu_state *rsp, int relaxed); static int rcu_pending(int cpu); /* * Return the number of RCU-sched batches processed thus far for debug & stats. */ long rcu_batches_completed_sched(void) { return rcu_sched_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_sched); /* * Return the number of RCU BH batches processed thus far for debug & stats. */ long rcu_batches_completed_bh(void) { return rcu_bh_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); /* * Force a quiescent state for RCU BH. */ void rcu_bh_force_quiescent_state(void) { force_quiescent_state(&rcu_bh_state, 0); } EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); /* * Record the number of times rcutorture tests have been initiated and * terminated. This information allows the debugfs tracing stats to be * correlated to the rcutorture messages, even when the rcutorture module * is being repeatedly loaded and unloaded. In other words, we cannot * store this state in rcutorture itself. */ void rcutorture_record_test_transition(void) { rcutorture_testseq++; rcutorture_vernum = 0; } EXPORT_SYMBOL_GPL(rcutorture_record_test_transition); /* * Record the number of writer passes through the current rcutorture test. * This is also used to correlate debugfs tracing stats with the rcutorture * messages. */ void rcutorture_record_progress(unsigned long vernum) { rcutorture_vernum++; } EXPORT_SYMBOL_GPL(rcutorture_record_progress); /* * Force a quiescent state for RCU-sched. */ void rcu_sched_force_quiescent_state(void) { force_quiescent_state(&rcu_sched_state, 0); } EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); /* * Does the CPU have callbacks ready to be invoked? */ static int cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) { return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]; } /* * Does the current CPU require a yet-as-unscheduled grace period? */ static int cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) { return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp); } /* * Return the root node of the specified rcu_state structure. */ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) { return &rsp->node[0]; } /* * If the specified CPU is offline, tell the caller that it is in * a quiescent state. Otherwise, whack it with a reschedule IPI. * Grace periods can end up waiting on an offline CPU when that * CPU is in the process of coming online -- it will be added to the * rcu_node bitmasks before it actually makes it online. The same thing * can happen while a CPU is in the process of coming online. Because this * race is quite rare, we check for it after detecting that the grace * period has been delayed rather than checking each and every CPU * each and every time we start a new grace period. */ static int rcu_implicit_offline_qs(struct rcu_data *rdp) { /* * If the CPU is offline for more than a jiffy, it is in a quiescent * state. We can trust its state not to change because interrupts * are disabled. The reason for the jiffy's worth of slack is to * handle CPUs initializing on the way up and finding their way * to the idle loop on the way down. */ if (cpu_is_offline(rdp->cpu) && ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl"); rdp->offline_fqs++; return 1; } return 0; } /* * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle * * If the new value of the ->dynticks_nesting counter now is zero, * we really have entered idle, and must do the appropriate accounting. * The caller must have disabled interrupts. */ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval) { trace_rcu_dyntick("Start", oldval, 0); if (!is_idle_task(current)) { struct task_struct *idle = idle_task(smp_processor_id()); trace_rcu_dyntick("Error on entry: not idle task", oldval, 0); ftrace_dump(DUMP_ALL); WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", current->pid, current->comm, idle->pid, idle->comm); /* must be idle task! */ } rcu_prepare_for_idle(smp_processor_id()); /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ smp_mb__before_atomic_inc(); /* See above. */ atomic_inc(&rdtp->dynticks); smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */ WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); /* * The idle task is not permitted to enter the idle loop while * in an RCU read-side critical section. */ rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), "Illegal idle entry in RCU read-side critical section."); rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), "Illegal idle entry in RCU-bh read-side critical section."); rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), "Illegal idle entry in RCU-sched read-side critical section."); } /** * rcu_idle_enter - inform RCU that current CPU is entering idle * * Enter idle mode, in other words, -leave- the mode in which RCU * read-side critical sections can occur. (Though RCU read-side * critical sections can occur in irq handlers in idle, a possibility * handled by irq_enter() and irq_exit().) * * We crowbar the ->dynticks_nesting field to zero to allow for * the possibility of usermode upcalls having messed up our count * of interrupt nesting level during the prior busy period. */ void rcu_idle_enter(void) { unsigned long flags; long long oldval; struct rcu_dynticks *rdtp; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); oldval = rdtp->dynticks_nesting; WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0); if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) rdtp->dynticks_nesting = 0; else rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; rcu_idle_enter_common(rdtp, oldval); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(rcu_idle_enter); /** * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle * * Exit from an interrupt handler, which might possibly result in entering * idle mode, in other words, leaving the mode in which read-side critical * sections can occur. * * This code assumes that the idle loop never does anything that might * result in unbalanced calls to irq_enter() and irq_exit(). If your * architecture violates this assumption, RCU will give you what you * deserve, good and hard. But very infrequently and irreproducibly. * * Use things like work queues to work around this limitation. * * You have been warned. */ void rcu_irq_exit(void) { unsigned long flags; long long oldval; struct rcu_dynticks *rdtp; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting--; WARN_ON_ONCE(rdtp->dynticks_nesting < 0); if (rdtp->dynticks_nesting) trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting); else rcu_idle_enter_common(rdtp, oldval); local_irq_restore(flags); } /* * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle * * If the new value of the ->dynticks_nesting counter was previously zero, * we really have exited idle, and must do the appropriate accounting. * The caller must have disabled interrupts. */ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) { smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */ atomic_inc(&rdtp->dynticks); /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ smp_mb__after_atomic_inc(); /* See above. */ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); rcu_cleanup_after_idle(smp_processor_id()); trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting); if (!is_idle_task(current)) { struct task_struct *idle = idle_task(smp_processor_id()); trace_rcu_dyntick("Error on exit: not idle task", oldval, rdtp->dynticks_nesting); ftrace_dump(DUMP_ALL); WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", current->pid, current->comm, idle->pid, idle->comm); /* must be idle task! */ } } /** * rcu_idle_exit - inform RCU that current CPU is leaving idle * * Exit idle mode, in other words, -enter- the mode in which RCU * read-side critical sections can occur. * * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to * allow for the possibility of usermode upcalls messing up our count * of interrupt nesting level during the busy period that is just * now starting. */ void rcu_idle_exit(void) { unsigned long flags; struct rcu_dynticks *rdtp; long long oldval; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); oldval = rdtp->dynticks_nesting; WARN_ON_ONCE(oldval < 0); if (oldval & DYNTICK_TASK_NEST_MASK) rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; else rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(rcu_idle_exit); /** * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle * * Enter an interrupt handler, which might possibly result in exiting * idle mode, in other words, entering the mode in which read-side critical * sections can occur. * * Note that the Linux kernel is fully capable of entering an interrupt * handler that it never exits, for example when doing upcalls to * user mode! This code assumes that the idle loop never does upcalls to * user mode. If your architecture does do upcalls from the idle loop (or * does anything else that results in unbalanced calls to the irq_enter() * and irq_exit() functions), RCU will give you what you deserve, good * and hard. But very infrequently and irreproducibly. * * Use things like work queues to work around this limitation. * * You have been warned. */ void rcu_irq_enter(void) { unsigned long flags; struct rcu_dynticks *rdtp; long long oldval; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting++; WARN_ON_ONCE(rdtp->dynticks_nesting == 0); if (oldval) trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting); else rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); } /** * rcu_nmi_enter - inform RCU of entry to NMI context * * If the CPU was idle with dynamic ticks active, and there is no * irq handler running, this updates rdtp->dynticks_nmi to let the * RCU grace-period handling know that the CPU is active. */ void rcu_nmi_enter(void) { struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); if (rdtp->dynticks_nmi_nesting == 0 && (atomic_read(&rdtp->dynticks) & 0x1)) return; rdtp->dynticks_nmi_nesting++; smp_mb__before_atomic_inc(); /* Force delay from prior write. */ atomic_inc(&rdtp->dynticks); /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ smp_mb__after_atomic_inc(); /* See above. */ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); } /** * rcu_nmi_exit - inform RCU of exit from NMI context * * If the CPU was idle with dynamic ticks active, and there is no * irq handler running, this updates rdtp->dynticks_nmi to let the * RCU grace-period handling know that the CPU is no longer active. */ void rcu_nmi_exit(void) { struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); if (rdtp->dynticks_nmi_nesting == 0 || --rdtp->dynticks_nmi_nesting != 0) return; /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ smp_mb__before_atomic_inc(); /* See above. */ atomic_inc(&rdtp->dynticks); smp_mb__after_atomic_inc(); /* Force delay to next write. */ WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); } #ifdef CONFIG_PROVE_RCU /** * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle * * If the current CPU is in its idle loop and is neither in an interrupt * or NMI handler, return true. */ int rcu_is_cpu_idle(void) { int ret; preempt_disable(); ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0; preempt_enable(); return ret; } EXPORT_SYMBOL(rcu_is_cpu_idle); #ifdef CONFIG_HOTPLUG_CPU /* * Is the current CPU online? Disable preemption to avoid false positives * that could otherwise happen due to the current CPU number being sampled, * this task being preempted, its old CPU being taken offline, resuming * on some other CPU, then determining that its old CPU is now offline. * It is OK to use RCU on an offline processor during initial boot, hence * the check for rcu_scheduler_fully_active. Note also that it is OK * for a CPU coming online to use RCU for one jiffy prior to marking itself * online in the cpu_online_mask. Similarly, it is OK for a CPU going * offline to continue to use RCU for one jiffy after marking itself * offline in the cpu_online_mask. This leniency is necessary given the * non-atomic nature of the online and offline processing, for example, * the fact that a CPU enters the scheduler after completing the CPU_DYING * notifiers. * * This is also why RCU internally marks CPUs online during the * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase. * * Disable checking if in an NMI handler because we cannot safely report * errors from NMI handlers anyway. */ bool rcu_lockdep_current_cpu_online(void) { struct rcu_data *rdp; struct rcu_node *rnp; bool ret; if (in_nmi()) return 1; preempt_disable(); rdp = &__get_cpu_var(rcu_sched_data); rnp = rdp->mynode; ret = (rdp->grpmask & rnp->qsmaskinit) || !rcu_scheduler_fully_active; preempt_enable(); return ret; } EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); #endif /* #ifdef CONFIG_HOTPLUG_CPU */ #endif /* #ifdef CONFIG_PROVE_RCU */ /** * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle * * If the current CPU is idle or running at a first-level (not nested) * interrupt from idle, return true. The caller must have at least * disabled preemption. */ int rcu_is_cpu_rrupt_from_idle(void) { return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1; } /* * Snapshot the specified CPU's dynticks counter so that we can later * credit them with an implicit quiescent state. Return 1 if this CPU * is in dynticks idle mode, which is an extended quiescent state. */ static int dyntick_save_progress_counter(struct rcu_data *rdp) { rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks); return (rdp->dynticks_snap & 0x1) == 0; } /* * Return true if the specified CPU has passed through a quiescent * state by virtue of being in or having passed through an dynticks * idle state since the last call to dyntick_save_progress_counter() * for this same CPU. */ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) { unsigned int curr; unsigned int snap; curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks); snap = (unsigned int)rdp->dynticks_snap; /* * If the CPU passed through or entered a dynticks idle phase with * no active irq/NMI handlers, then we can safely pretend that the CPU * already acknowledged the request to pass through a quiescent * state. Either way, that CPU cannot possibly be in an RCU * read-side critical section that started before the beginning * of the current RCU grace period. */ if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "dti"); rdp->dynticks_fqs++; return 1; } /* Go check for the CPU being offline. */ return rcu_implicit_offline_qs(rdp); } static int jiffies_till_stall_check(void) { int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); /* * Limit check must be consistent with the Kconfig limits * for CONFIG_RCU_CPU_STALL_TIMEOUT. */ if (till_stall_check < 3) { ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; till_stall_check = 3; } else if (till_stall_check > 300) { ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; till_stall_check = 300; } return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; } static void record_gp_stall_check_time(struct rcu_state *rsp) { rsp->gp_start = jiffies; rsp->jiffies_stall = jiffies + jiffies_till_stall_check(); } static void print_other_cpu_stall(struct rcu_state *rsp) { int cpu; long delta; unsigned long flags; int ndetected; struct rcu_node *rnp = rcu_get_root(rsp); /* Only let one CPU complain about others per time interval. */ raw_spin_lock_irqsave(&rnp->lock, flags); delta = jiffies - rsp->jiffies_stall; if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3; raw_spin_unlock_irqrestore(&rnp->lock, flags); /* * OK, time to rat on our buddy... * See Documentation/RCU/stallwarn.txt for info on how to debug * RCU CPU stall warnings. */ printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:", rsp->name); print_cpu_stall_info_begin(); rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); ndetected += rcu_print_task_stall(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); if (rnp->qsmask == 0) continue; for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) if (rnp->qsmask & (1UL << cpu)) { print_cpu_stall_info(rsp, rnp->grplo + cpu); ndetected++; } } /* * Now rat on any tasks that got kicked up to the root rcu_node * due to CPU offlining. */ rnp = rcu_get_root(rsp); raw_spin_lock_irqsave(&rnp->lock, flags); ndetected = rcu_print_task_stall(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); print_cpu_stall_info_end(); printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n", smp_processor_id(), (long)(jiffies - rsp->gp_start)); if (ndetected == 0) printk(KERN_ERR "INFO: Stall ended before state dump start\n"); else if (!trigger_all_cpu_backtrace()) dump_stack(); /* If so configured, complain about tasks blocking the grace period. */ rcu_print_detail_task_stall(rsp); force_quiescent_state(rsp, 0); /* Kick them all. */ } static void print_cpu_stall(struct rcu_state *rsp) { unsigned long flags; struct rcu_node *rnp = rcu_get_root(rsp); /* * OK, time to rat on ourselves... * See Documentation/RCU/stallwarn.txt for info on how to debug * RCU CPU stall warnings. */ printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name); print_cpu_stall_info_begin(); print_cpu_stall_info(rsp, smp_processor_id()); print_cpu_stall_info_end(); printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start); if (!trigger_all_cpu_backtrace()) dump_stack(); raw_spin_lock_irqsave(&rnp->lock, flags); if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall)) rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3; raw_spin_unlock_irqrestore(&rnp->lock, flags); set_need_resched(); /* kick ourselves to get things going. */ } static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long j; unsigned long js; struct rcu_node *rnp; if (rcu_cpu_stall_suppress) return; j = ACCESS_ONCE(jiffies); js = ACCESS_ONCE(rsp->jiffies_stall); rnp = rdp->mynode; if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); } else if (rcu_gp_in_progress(rsp) && ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) { /* They had a few time units to dump stack, so complain. */ print_other_cpu_stall(rsp); } } static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) { rcu_cpu_stall_suppress = 1; return NOTIFY_DONE; } /** * rcu_cpu_stall_reset - prevent further stall warnings in current grace period * * Set the stall-warning timeout way off into the future, thus preventing * any RCU CPU stall-warning messages from appearing in the current set of * RCU grace periods. * * The caller must disable hard irqs. */ void rcu_cpu_stall_reset(void) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) rsp->jiffies_stall = jiffies + ULONG_MAX / 2; } static struct notifier_block rcu_panic_block = { .notifier_call = rcu_panic, }; static void __init check_cpu_stall_init(void) { atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); } /* * Update CPU-local rcu_data state to record the newly noticed grace period. * This is used both when we started the grace period and when we notice * that someone else started the grace period. The caller must hold the * ->lock of the leaf rcu_node structure corresponding to the current CPU, * and must have irqs disabled. */ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { if (rdp->gpnum != rnp->gpnum) { /* * If the current grace period is waiting for this CPU, * set up to detect a quiescent state, otherwise don't * go looking for one. */ rdp->gpnum = rnp->gpnum; trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart"); if (rnp->qsmask & rdp->grpmask) { rdp->qs_pending = 1; rdp->passed_quiesce = 0; } else rdp->qs_pending = 0; zero_cpu_stall_ticks(rdp); } } static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; struct rcu_node *rnp; local_irq_save(flags); rnp = rdp->mynode; if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */ !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */ local_irq_restore(flags); return; } __note_new_gpnum(rsp, rnp, rdp); raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * Did someone else start a new RCU grace period start since we last * checked? Update local state appropriately if so. Must be called * on the CPU corresponding to rdp. */ static int check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; int ret = 0; local_irq_save(flags); if (rdp->gpnum != rsp->gpnum) { note_new_gpnum(rsp, rdp); ret = 1; } local_irq_restore(flags); return ret; } /* * Advance this CPU's callbacks, but only if the current grace period * has ended. This may be called only from the CPU to whom the rdp * belongs. In addition, the corresponding leaf rcu_node structure's * ->lock must be held by the caller, with irqs disabled. */ static void __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { /* Did another grace period end? */ if (rdp->completed != rnp->completed) { /* Advance callbacks. No harm if list empty. */ rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL]; rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL]; rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; /* Remember that we saw this grace-period completion. */ rdp->completed = rnp->completed; trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuend"); /* * If we were in an extended quiescent state, we may have * missed some grace periods that others CPUs handled on * our behalf. Catch up with this state to avoid noting * spurious new grace periods. If another grace period * has started, then rnp->gpnum will have advanced, so * we will detect this later on. */ if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) rdp->gpnum = rdp->completed; /* * If RCU does not need a quiescent state from this CPU, * then make sure that this CPU doesn't go looking for one. */ if ((rnp->qsmask & rdp->grpmask) == 0) rdp->qs_pending = 0; } } /* * Advance this CPU's callbacks, but only if the current grace period * has ended. This may be called only from the CPU to whom the rdp * belongs. */ static void rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; struct rcu_node *rnp; local_irq_save(flags); rnp = rdp->mynode; if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */ !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */ local_irq_restore(flags); return; } __rcu_process_gp_end(rsp, rnp, rdp); raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * Do per-CPU grace-period initialization for running CPU. The caller * must hold the lock of the leaf rcu_node structure corresponding to * this CPU. */ static void rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { /* Prior grace period ended, so advance callbacks for current CPU. */ __rcu_process_gp_end(rsp, rnp, rdp); /* * Because this CPU just now started the new grace period, we know * that all of its callbacks will be covered by this upcoming grace * period, even the ones that were registered arbitrarily recently. * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL. * * Other CPUs cannot be sure exactly when the grace period started. * Therefore, their recently registered callbacks must pass through * an additional RCU_NEXT_READY stage, so that they will be handled * by the next RCU grace period. */ rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; /* Set state so that this CPU will detect the next quiescent state. */ __note_new_gpnum(rsp, rnp, rdp); } /* * Start a new RCU grace period if warranted, re-initializing the hierarchy * in preparation for detecting the next grace period. The caller must hold * the root node's ->lock, which is released before return. Hard irqs must * be disabled. * * Note that it is legal for a dying CPU (which is marked as offline) to * invoke this function. This can happen when the dying CPU reports its * quiescent state. */ static void rcu_start_gp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); if (!rcu_scheduler_fully_active || !cpu_needs_another_gp(rsp, rdp)) { /* * Either the scheduler hasn't yet spawned the first * non-idle task or this CPU does not need another * grace period. Either way, don't start a new grace * period. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } if (rsp->fqs_active) { /* * This CPU needs a grace period, but force_quiescent_state() * is running. Tell it to start one on this CPU's behalf. */ rsp->fqs_need_gp = 1; raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } /* Advance to a new grace period and initialize state. */ rsp->gpnum++; trace_rcu_grace_period(rsp->name, rsp->gpnum, "start"); WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT); rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ /* Exclude any concurrent CPU-hotplug operations. */ raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ /* * Set the quiescent-state-needed bits in all the rcu_node * structures for all currently online CPUs in breadth-first * order, starting from the root rcu_node structure. This * operation relies on the layout of the hierarchy within the * rsp->node[] array. Note that other CPUs will access only * the leaves of the hierarchy, which still indicate that no * grace period is in progress, at least until the corresponding * leaf node has been initialized. In addition, we have excluded * CPU-hotplug operations. * * Note that the grace period cannot complete until we finish * the initialization process, as there will be at least one * qsmask bit set in the root node until that time, namely the * one corresponding to this CPU, due to the fact that we have * irqs disabled. */ rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; rnp->gpnum = rsp->gpnum; rnp->completed = rsp->completed; if (rnp == rdp->mynode) rcu_start_gp_per_cpu(rsp, rnp, rdp); rcu_preempt_boost_start_gp(rnp); trace_rcu_grace_period_init(rsp->name, rnp->gpnum, rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } rnp = rcu_get_root(rsp); raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */ raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ raw_spin_unlock_irqrestore(&rsp->onofflock, flags); } /* * Report a full set of quiescent states to the specified rcu_state * data structure. This involves cleaning up after the prior grace * period and letting rcu_start_gp() start up the next grace period * if one is needed. Note that the caller must hold rnp->lock, as * required by rcu_start_gp(), which will release it. */ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { unsigned long gp_duration; struct rcu_node *rnp = rcu_get_root(rsp); struct rcu_data *rdp = this_cpu_ptr(rsp->rda); WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); /* * Ensure that all grace-period and pre-grace-period activity * is seen before the assignment to rsp->completed. */ smp_mb(); /* See above block comment. */ gp_duration = jiffies - rsp->gp_start; if (gp_duration > rsp->gp_max) rsp->gp_max = gp_duration; /* * We know the grace period is complete, but to everyone else * it appears to still be ongoing. But it is also the case * that to everyone else it looks like there is nothing that * they can do to advance the grace period. It is therefore * safe for us to drop the lock in order to mark the grace * period as completed in all of the rcu_node structures. * * But if this CPU needs another grace period, it will take * care of this while initializing the next grace period. * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL * because the callbacks have not yet been advanced: Those * callbacks are waiting on the grace period that just now * completed. */ if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ /* * Propagate new ->completed value to rcu_node structures * so that other CPUs don't have to wait until the start * of the next grace period to process their callbacks. */ rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rnp->completed = rsp->gpnum; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } rnp = rcu_get_root(rsp); raw_spin_lock(&rnp->lock); /* irqs already disabled. */ } rsp->completed = rsp->gpnum; /* Declare the grace period complete. */ trace_rcu_grace_period(rsp->name, rsp->completed, "end"); rsp->fqs_state = RCU_GP_IDLE; rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ } /* * Similar to rcu_report_qs_rdp(), for which it is a helper function. * Allows quiescent states for a group of CPUs to be reported at one go * to the specified rcu_node structure, though all the CPUs in the group * must be represented by the same rcu_node structure (which need not be * a leaf rcu_node structure, though it often will be). That structure's * lock must be held upon entry, and it is released before return. */ static void rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { struct rcu_node *rnp_c; /* Walk up the rcu_node hierarchy. */ for (;;) { if (!(rnp->qsmask & mask)) { /* Our bit has already been cleared, so done. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } rnp->qsmask &= ~mask; trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum, mask, rnp->qsmask, rnp->level, rnp->grplo, rnp->grphi, !!rnp->gp_tasks); if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { /* Other bits still set at this level, so done. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } mask = rnp->grpmask; if (rnp->parent == NULL) { /* No more levels. Exit loop holding root lock. */ break; } raw_spin_unlock_irqrestore(&rnp->lock, flags); rnp_c = rnp; rnp = rnp->parent; raw_spin_lock_irqsave(&rnp->lock, flags); WARN_ON_ONCE(rnp_c->qsmask); } /* * Get here if we are the last CPU to pass through a quiescent * state for this grace period. Invoke rcu_report_qs_rsp() * to clean up and start the next grace period if one is needed. */ rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */ } /* * Record a quiescent state for the specified CPU to that CPU's rcu_data * structure. This must be either called from the specified CPU, or * called when the specified CPU is known to be offline (and when it is * also known that no other CPU is concurrently trying to help the offline * CPU). The lastcomp argument is used to make sure we are still in the * grace period of interest. We don't want to end the current grace period * based on quiescent states detected in an earlier grace period! */ static void rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastgp) { unsigned long flags; unsigned long mask; struct rcu_node *rnp; rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); if (lastgp != rnp->gpnum || rnp->completed == rnp->gpnum) { /* * The grace period in which this quiescent state was * recorded has ended, so don't report it upwards. * We will instead need a new quiescent state that lies * within the current grace period. */ rdp->passed_quiesce = 0; /* need qs for new gp. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } mask = rdp->grpmask; if ((rnp->qsmask & mask) == 0) { raw_spin_unlock_irqrestore(&rnp->lock, flags); } else { rdp->qs_pending = 0; /* * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. */ rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */ } } /* * Check to see if there is a new grace period of which this CPU * is not yet aware, and if so, set up local rcu_data state for it. * Otherwise, see if this CPU has just passed through its first * quiescent state for this grace period, and record that fact if so. */ static void rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) { /* If there is now a new grace period, record and return. */ if (check_for_new_grace_period(rsp, rdp)) return; /* * Does this CPU still need to do its part for current grace period? * If no, return and let the other CPUs do their part as well. */ if (!rdp->qs_pending) return; /* * Was there a quiescent state since the beginning of the grace * period? If no, then exit and wait for the next call. */ if (!rdp->passed_quiesce) return; /* * Tell RCU we are done (but rcu_report_qs_rdp() will be the * judge of that). */ rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesce_gpnum); } #ifdef CONFIG_HOTPLUG_CPU /* * Send the specified CPU's RCU callbacks to the orphanage. The * specified CPU must be offline, and the caller must hold the * ->onofflock. */ static void rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { int i; /* * Orphan the callbacks. First adjust the counts. This is safe * because ->onofflock excludes _rcu_barrier()'s adoption of * the callbacks, thus no memory barrier is required. */ if (rdp->nxtlist != NULL) { rsp->qlen_lazy += rdp->qlen_lazy; rsp->qlen += rdp->qlen; rdp->n_cbs_orphaned += rdp->qlen; rdp->qlen_lazy = 0; rdp->qlen = 0; } /* * Next, move those callbacks still needing a grace period to * the orphanage, where some other CPU will pick them up. * Some of the callbacks might have gone partway through a grace * period, but that is too bad. They get to start over because we * cannot assume that grace periods are synchronized across CPUs. * We don't bother updating the ->nxttail[] array yet, instead * we just reset the whole thing later on. */ if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) { *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL]; rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = NULL; } /* * Then move the ready-to-invoke callbacks to the orphanage, * where some other CPU will pick them up. These will not be * required to pass though another grace period: They are done. */ if (rdp->nxtlist != NULL) { *rsp->orphan_donetail = rdp->nxtlist; rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL]; } /* Finally, initialize the rcu_data structure's list to empty. */ rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; } /* * Adopt the RCU callbacks from the specified rcu_state structure's * orphanage. The caller must hold the ->onofflock. */ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) { int i; struct rcu_data *rdp = __this_cpu_ptr(rsp->rda); /* * If there is an rcu_barrier() operation in progress, then * only the task doing that operation is permitted to adopt * callbacks. To do otherwise breaks rcu_barrier() and friends * by causing them to fail to wait for the callbacks in the * orphanage. */ if (rsp->rcu_barrier_in_progress && rsp->rcu_barrier_in_progress != current) return; /* Do the accounting first. */ rdp->qlen_lazy += rsp->qlen_lazy; rdp->qlen += rsp->qlen; rdp->n_cbs_adopted += rsp->qlen; if (rsp->qlen_lazy != rsp->qlen) rcu_idle_count_callbacks_posted(); rsp->qlen_lazy = 0; rsp->qlen = 0; /* * We do not need a memory barrier here because the only way we * can get here if there is an rcu_barrier() in flight is if * we are the task doing the rcu_barrier(). */ /* First adopt the ready-to-invoke callbacks. */ if (rsp->orphan_donelist != NULL) { *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist; for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--) if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL]) rdp->nxttail[i] = rsp->orphan_donetail; rsp->orphan_donelist = NULL; rsp->orphan_donetail = &rsp->orphan_donelist; } /* And then adopt the callbacks that still need a grace period. */ if (rsp->orphan_nxtlist != NULL) { *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist; rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail; rsp->orphan_nxtlist = NULL; rsp->orphan_nxttail = &rsp->orphan_nxtlist; } } /* * Trace the fact that this CPU is going offline. */ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { RCU_TRACE(unsigned long mask); RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda)); RCU_TRACE(struct rcu_node *rnp = rdp->mynode); RCU_TRACE(mask = rdp->grpmask); trace_rcu_grace_period(rsp->name, rnp->gpnum + 1 - !!(rnp->qsmask & mask), "cpuofl"); } /* * The CPU has been completely removed, and some other CPU is reporting * this fact from process context. Do the remainder of the cleanup, * including orphaning the outgoing CPU's RCU callbacks, and also * adopting them, if there is no _rcu_barrier() instance running. * There can only be one CPU hotplug operation at a time, so no other * CPU can be attempting to update rcu_cpu_kthread_task. */ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { unsigned long flags; unsigned long mask; int need_report = 0; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ /* Adjust any no-longer-needed kthreads. */ rcu_stop_cpu_kthread(cpu); rcu_node_kthread_setaffinity(rnp, -1); /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */ /* Exclude any attempts to start a new grace period. */ raw_spin_lock_irqsave(&rsp->onofflock, flags); /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */ rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp); rcu_adopt_orphan_cbs(rsp); /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */ mask = rdp->grpmask; /* rnp->grplo is constant. */ do { raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rnp->qsmaskinit &= ~mask; if (rnp->qsmaskinit != 0) { if (rnp != rdp->mynode) raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ break; } if (rnp == rdp->mynode) need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp); else raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ mask = rnp->grpmask; rnp = rnp->parent; } while (rnp != NULL); /* * We still hold the leaf rcu_node structure lock here, and * irqs are still disabled. The reason for this subterfuge is * because invoking rcu_report_unblock_qs_rnp() with ->onofflock * held leads to deadlock. */ raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ rnp = rdp->mynode; if (need_report & RCU_OFL_TASKS_NORM_GP) rcu_report_unblock_qs_rnp(rnp, flags); else raw_spin_unlock_irqrestore(&rnp->lock, flags); if (need_report & RCU_OFL_TASKS_EXP_GP) rcu_report_exp_rnp(rsp, rnp, true); } #else /* #ifdef CONFIG_HOTPLUG_CPU */ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) { } static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { } static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { } #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */ /* * Invoke any RCU callbacks that have made it to the end of their grace * period. Thottle as specified by rdp->blimit. */ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; struct rcu_head *next, *list, **tail; int bl, count, count_lazy, i; /* If no callbacks are ready, just return.*/ if (!cpu_has_callbacks_ready_to_invoke(rdp)) { trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0); trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist), need_resched(), is_idle_task(current), rcu_is_callbacks_kthread()); return; } /* * Extract the list of ready callbacks, disabling to prevent * races with call_rcu() from interrupt handlers. */ local_irq_save(flags); WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); bl = rdp->blimit; trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl); list = rdp->nxtlist; rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = NULL; tail = rdp->nxttail[RCU_DONE_TAIL]; for (i = RCU_NEXT_SIZE - 1; i >= 0; i--) if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL]) rdp->nxttail[i] = &rdp->nxtlist; local_irq_restore(flags); /* Invoke callbacks. */ count = count_lazy = 0; while (list) { next = list->next; prefetch(next); debug_rcu_head_unqueue(list); if (__rcu_reclaim(rsp->name, list)) count_lazy++; list = next; /* Stop only if limit reached and CPU has something to do. */ if (++count >= bl && (need_resched() || (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) break; } local_irq_save(flags); trace_rcu_batch_end(rsp->name, count, !!list, need_resched(), is_idle_task(current), rcu_is_callbacks_kthread()); /* Update count, and requeue any remaining callbacks. */ if (list != NULL) { *tail = rdp->nxtlist; rdp->nxtlist = list; for (i = 0; i < RCU_NEXT_SIZE; i++) if (&rdp->nxtlist == rdp->nxttail[i]) rdp->nxttail[i] = tail; else break; } smp_mb(); /* List handling before counting for rcu_barrier(). */ rdp->qlen_lazy -= count_lazy; rdp->qlen -= count; rdp->n_cbs_invoked += count; /* Reinstate batch limit if we have worked down the excess. */ if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark) rdp->blimit = blimit; /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) { rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark) rdp->qlen_last_fqs_check = rdp->qlen; local_irq_restore(flags); /* Re-invoke RCU core processing if there are callbacks remaining. */ if (cpu_has_callbacks_ready_to_invoke(rdp)) invoke_rcu_core(); } /* * Check to see if this CPU is in a non-context-switch quiescent state * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). * Also schedule RCU core processing. * * This function must be called from hardirq context. It is normally * invoked from the scheduling-clock interrupt. If rcu_pending returns * false, there is no point in invoking rcu_check_callbacks(). */ void rcu_check_callbacks(int cpu, int user) { trace_rcu_utilization("Start scheduler-tick"); increment_cpu_stall_ticks(); if (user || rcu_is_cpu_rrupt_from_idle()) { /* * Get here if this CPU took its interrupt from user * mode or from the idle loop, and if this is not a * nested interrupt. In this case, the CPU is in * a quiescent state, so note it. * * No memory barrier is required here because both * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local * variables that other CPUs neither access nor modify, * at least not while the corresponding CPU is online. */ rcu_sched_qs(cpu); rcu_bh_qs(cpu); } else if (!in_softirq()) { /* * Get here if this CPU did not take its interrupt from * softirq, in other words, if it is not interrupting * a rcu_bh read-side critical section. This is an _bh * critical section, so note it. */ rcu_bh_qs(cpu); } rcu_preempt_check_callbacks(cpu); if (rcu_pending(cpu)) invoke_rcu_core(); trace_rcu_utilization("End scheduler-tick"); } /* * Scan the leaf rcu_node structures, processing dyntick state for any that * have not yet encountered a quiescent state, using the function specified. * Also initiate boosting for any threads blocked on the root rcu_node. * * The caller must have suppressed start of new grace periods. */ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) { unsigned long bit; int cpu; unsigned long flags; unsigned long mask; struct rcu_node *rnp; rcu_for_each_leaf_node(rsp, rnp) { mask = 0; raw_spin_lock_irqsave(&rnp->lock, flags); if (!rcu_gp_in_progress(rsp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } if (rnp->qsmask == 0) { rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ continue; } cpu = rnp->grplo; bit = 1; for (; cpu <= rnp->grphi; cpu++, bit <<= 1) { if ((rnp->qsmask & bit) != 0 && f(per_cpu_ptr(rsp->rda, cpu))) mask |= bit; } if (mask != 0) { /* rcu_report_qs_rnp() releases rnp->lock. */ rcu_report_qs_rnp(mask, rsp, rnp, flags); continue; } raw_spin_unlock_irqrestore(&rnp->lock, flags); } rnp = rcu_get_root(rsp); if (rnp->qsmask == 0) { raw_spin_lock_irqsave(&rnp->lock, flags); rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ } } /* * Force quiescent states on reluctant CPUs, and also detect which * CPUs are in dyntick-idle mode. */ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) { unsigned long flags; struct rcu_node *rnp = rcu_get_root(rsp); trace_rcu_utilization("Start fqs"); if (!rcu_gp_in_progress(rsp)) { trace_rcu_utilization("End fqs"); return; /* No grace period in progress, nothing to force. */ } if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) { rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */ trace_rcu_utilization("End fqs"); return; /* Someone else is already on the job. */ } if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies)) goto unlock_fqs_ret; /* no emergency and done recently. */ rsp->n_force_qs++; raw_spin_lock(&rnp->lock); /* irqs already disabled */ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; if(!rcu_gp_in_progress(rsp)) { rsp->n_force_qs_ngp++; raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ goto unlock_fqs_ret; /* no GP in progress, time updated. */ } rsp->fqs_active = 1; switch (rsp->fqs_state) { case RCU_GP_IDLE: case RCU_GP_INIT: break; /* grace period idle or initializing, ignore. */ case RCU_SAVE_DYNTICK: if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK) break; /* So gcc recognizes the dead code. */ raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ /* Record dyntick-idle state. */ force_qs_rnp(rsp, dyntick_save_progress_counter); raw_spin_lock(&rnp->lock); /* irqs already disabled */ if (rcu_gp_in_progress(rsp)) rsp->fqs_state = RCU_FORCE_QS; break; case RCU_FORCE_QS: /* Check dyntick-idle state, send IPI to laggarts. */ raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ force_qs_rnp(rsp, rcu_implicit_dynticks_qs); /* Leave state in case more forcing is required. */ raw_spin_lock(&rnp->lock); /* irqs already disabled */ break; } rsp->fqs_active = 0; if (rsp->fqs_need_gp) { raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */ rsp->fqs_need_gp = 0; rcu_start_gp(rsp, flags); /* releases rnp->lock */ trace_rcu_utilization("End fqs"); return; } raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ unlock_fqs_ret: raw_spin_unlock_irqrestore(&rsp->fqslock, flags); trace_rcu_utilization("End fqs"); } /* * This does the RCU core processing work for the specified rcu_state * and rcu_data structures. This may be called only from the CPU to * whom the rdp belongs. */ static void __rcu_process_callbacks(struct rcu_state *rsp) { unsigned long flags; struct rcu_data *rdp = __this_cpu_ptr(rsp->rda); WARN_ON_ONCE(rdp->beenonline == 0); /* * If an RCU GP has gone long enough, go check for dyntick * idle CPUs and, if needed, send resched IPIs. */ if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) force_quiescent_state(rsp, 1); /* * Advance callbacks in response to end of earlier grace * period that some other CPU ended. */ rcu_process_gp_end(rsp, rdp); /* Update RCU state based on any recent quiescent states. */ rcu_check_quiescent_state(rsp, rdp); /* Does this CPU require a not-yet-started grace period? */ if (cpu_needs_another_gp(rsp, rdp)) { raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags); rcu_start_gp(rsp, flags); /* releases above lock */ } /* If there are callbacks ready, invoke them. */ if (cpu_has_callbacks_ready_to_invoke(rdp)) invoke_rcu_callbacks(rsp, rdp); } /* * Do RCU core processing for the current CPU. */ static void rcu_process_callbacks(struct softirq_action *unused) { struct rcu_state *rsp; trace_rcu_utilization("Start RCU core"); for_each_rcu_flavor(rsp) __rcu_process_callbacks(rsp); trace_rcu_utilization("End RCU core"); } /* * Schedule RCU callback invocation. If the specified type of RCU * does not support RCU priority boosting, just do a direct call, * otherwise wake up the per-CPU kernel kthread. Note that because we * are running on the current CPU with interrupts disabled, the * rcu_cpu_kthread_task cannot disappear out from under us. */ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) { if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active))) return; if (likely(!rsp->boost)) { rcu_do_batch(rsp, rdp); return; } invoke_rcu_callbacks_kthread(); } static void invoke_rcu_core(void) { raise_softirq(RCU_SOFTIRQ); } static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), struct rcu_state *rsp, bool lazy) { unsigned long flags; struct rcu_data *rdp; WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ debug_rcu_head_queue(head); head->func = func; head->next = NULL; smp_mb(); /* Ensure RCU update seen before callback registry. */ /* * Opportunistically note grace-period endings and beginnings. * Note that we might see a beginning right after we see an * end, but never vice versa, since this CPU has to pass through * a quiescent state betweentimes. */ local_irq_save(flags); rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */ rdp->qlen++; if (lazy) rdp->qlen_lazy++; else rcu_idle_count_callbacks_posted(); smp_mb(); /* Count before adding callback for rcu_barrier(). */ *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; if (__is_kfree_rcu_offset((unsigned long)func)) trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func, rdp->qlen_lazy, rdp->qlen); else trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen); /* If interrupts were disabled, don't dive into RCU core. */ if (irqs_disabled_flags(flags)) { local_irq_restore(flags); return; } /* * Force the grace period if too many callbacks or too long waiting. * Enforce hysteresis, and don't invoke force_quiescent_state() * if some other CPU has recently done so. Also, don't bother * invoking force_quiescent_state() if the newly enqueued callback * is the only one waiting for a grace period to complete. */ if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) { /* Are we ignoring a completed grace period? */ rcu_process_gp_end(rsp, rdp); check_for_new_grace_period(rsp, rdp); /* Start a new grace period if one not already started. */ if (!rcu_gp_in_progress(rsp)) { unsigned long nestflag; struct rcu_node *rnp_root = rcu_get_root(rsp); raw_spin_lock_irqsave(&rnp_root->lock, nestflag); rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */ } else { /* Give the grace period a kick. */ rdp->blimit = LONG_MAX; if (rsp->n_force_qs == rdp->n_force_qs_snap && *rdp->nxttail[RCU_DONE_TAIL] != head) force_quiescent_state(rsp, 0); rdp->n_force_qs_snap = rsp->n_force_qs; rdp->qlen_last_fqs_check = rdp->qlen; } } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) force_quiescent_state(rsp, 1); local_irq_restore(flags); } /* * Queue an RCU-sched callback for invocation after a grace period. */ void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_sched_state, 0); } EXPORT_SYMBOL_GPL(call_rcu_sched); /* * Queue an RCU callback for invocation after a quicker grace period. */ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_bh_state, 0); } EXPORT_SYMBOL_GPL(call_rcu_bh); /* * Because a context switch is a grace period for RCU-sched and RCU-bh, * any blocking grace-period wait automatically implies a grace period * if there is only one CPU online at any point time during execution * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to * occasionally incorrectly indicate that there are multiple CPUs online * when there was in fact only one the whole time, as this just adds * some overhead: RCU still operates correctly. * * Of course, sampling num_online_cpus() with preemption enabled can * give erroneous results if there are concurrent CPU-hotplug operations. * For example, given a demonic sequence of preemptions in num_online_cpus() * and CPU-hotplug operations, there could be two or more CPUs online at * all times, but num_online_cpus() might well return one (or even zero). * * However, all such demonic sequences require at least one CPU-offline * operation. Furthermore, rcu_blocking_is_gp() giving the wrong answer * is only a problem if there is an RCU read-side critical section executing * throughout. But RCU-sched and RCU-bh read-side critical sections * disable either preemption or bh, which prevents a CPU from going offline. * Therefore, the only way that rcu_blocking_is_gp() can incorrectly return * that there is only one CPU when in fact there was more than one throughout * is when there were no RCU readers in the system. If there are no * RCU readers, the grace period by definition can be of zero length, * regardless of the number of online CPUs. */ static inline int rcu_blocking_is_gp(void) { might_sleep(); /* Check for RCU read-side critical section. */ return num_online_cpus() <= 1; } /** * synchronize_sched - wait until an rcu-sched grace period has elapsed. * * Control will return to the caller some time after a full rcu-sched * grace period has elapsed, in other words after all currently executing * rcu-sched read-side critical sections have completed. These read-side * critical sections are delimited by rcu_read_lock_sched() and * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(), * local_irq_disable(), and so on may be used in place of * rcu_read_lock_sched(). * * This means that all preempt_disable code sequences, including NMI and * hardware-interrupt handlers, in progress on entry will have completed * before this primitive returns. However, this does not guarantee that * softirq handlers will have completed, since in some kernels, these * handlers can run in process context, and can block. * * This primitive provides the guarantees made by the (now removed) * synchronize_kernel() API. In contrast, synchronize_rcu() only * guarantees that rcu_read_lock() sections will have completed. * In "classic RCU", these two guarantees happen to be one and * the same, but can differ in realtime RCU implementations. */ void synchronize_sched(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_sched() in RCU-sched read-side critical section"); if (rcu_blocking_is_gp()) return; wait_rcu_gp(call_rcu_sched); } EXPORT_SYMBOL_GPL(synchronize_sched); /** * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. * * Control will return to the caller some time after a full rcu_bh grace * period has elapsed, in other words after all currently executing rcu_bh * read-side critical sections have completed. RCU read-side critical * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(), * and may be nested. */ void synchronize_rcu_bh(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_bh() in RCU-bh read-side critical section"); if (rcu_blocking_is_gp()) return; wait_rcu_gp(call_rcu_bh); } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); 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; } /** * synchronize_sched_expedited - Brute-force RCU-sched grace period * * Wait for an RCU-sched grace period to elapse, but use a "big hammer" * approach to force the grace period to end quickly. 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_sched_expedited() in a loop, please * restructure your code to batch your updates, and then use a single * synchronize_sched() instead. * * Note that it is illegal to call this function while holding any lock * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal * to call this function from a CPU-hotplug notifier. Failing to observe * these restriction will result in deadlock. * * 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(); WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id())); /* * 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); 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); /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, for the specified type of RCU, returning 1 if so. * The checks are in order of increasing expense: checks that can be * carried out against CPU-local state are performed first. However, * we must check for CPU stalls first, else we might not get a chance. */ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) { struct rcu_node *rnp = rdp->mynode; rdp->n_rcu_pending++; /* Check for CPU stalls, if enabled. */ check_cpu_stall(rsp, rdp); /* Is the RCU core waiting for a quiescent state from this CPU? */ if (rcu_scheduler_fully_active && rdp->qs_pending && !rdp->passed_quiesce) { /* * If force_quiescent_state() coming soon and this CPU * needs a quiescent state, and this is either RCU-sched * or RCU-bh, force a local reschedule. */ rdp->n_rp_qs_pending++; if (!rdp->preemptible && ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1, jiffies)) set_need_resched(); } else if (rdp->qs_pending && rdp->passed_quiesce) { rdp->n_rp_report_qs++; return 1; } /* Does this CPU have callbacks ready to invoke? */ if (cpu_has_callbacks_ready_to_invoke(rdp)) { rdp->n_rp_cb_ready++; return 1; } /* Has RCU gone idle with this CPU needing another grace period? */ if (cpu_needs_another_gp(rsp, rdp)) { rdp->n_rp_cpu_needs_gp++; return 1; } /* Has another RCU grace period completed? */ if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */ rdp->n_rp_gp_completed++; return 1; } /* Has a new RCU grace period started? */ if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */ rdp->n_rp_gp_started++; return 1; } /* Has an RCU GP gone long enough to send resched IPIs &c? */ if (rcu_gp_in_progress(rsp) && ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) { rdp->n_rp_need_fqs++; return 1; } /* nothing to do */ rdp->n_rp_need_nothing++; return 0; } /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, returning 1 if so. This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */ static int rcu_pending(int cpu) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu))) return 1; return 0; } /* * 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. */ static int rcu_cpu_has_callbacks(int cpu) { struct rcu_state *rsp; /* RCU callbacks either ready or pending? */ for_each_rcu_flavor(rsp) if (per_cpu_ptr(rsp->rda, cpu)->nxtlist) return 1; return 0; } /* * Helper function for _rcu_barrier() tracing. If tracing is disabled, * the compiler is expected to optimize this away. */ static void _rcu_barrier_trace(struct rcu_state *rsp, char *s, int cpu, unsigned long done) { trace_rcu_barrier(rsp->name, s, cpu, atomic_read(&rsp->barrier_cpu_count), done); } /* * RCU callback function for _rcu_barrier(). If we are last, wake * up the task executing _rcu_barrier(). */ static void rcu_barrier_callback(struct rcu_head *rhp) { struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head); struct rcu_state *rsp = rdp->rsp; if (atomic_dec_and_test(&rsp->barrier_cpu_count)) { _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done); complete(&rsp->barrier_completion); } else { _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done); } } /* * Called with preemption disabled, and from cross-cpu IRQ context. */ static void rcu_barrier_func(void *type) { struct rcu_state *rsp = type; struct rcu_data *rdp = __this_cpu_ptr(rsp->rda); _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done); atomic_inc(&rsp->barrier_cpu_count); rsp->call(&rdp->barrier_head, rcu_barrier_callback); } /* * Orchestrate the specified type of RCU barrier, waiting for all * RCU callbacks of the specified type to complete. */ static void _rcu_barrier(struct rcu_state *rsp) { int cpu; unsigned long flags; struct rcu_data *rdp; struct rcu_data rd; unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done); unsigned long snap_done; init_rcu_head_on_stack(&rd.barrier_head); _rcu_barrier_trace(rsp, "Begin", -1, snap); /* Take mutex to serialize concurrent rcu_barrier() requests. */ mutex_lock(&rsp->barrier_mutex); /* * Ensure that all prior references, including to ->n_barrier_done, * are ordered before the _rcu_barrier() machinery. */ smp_mb(); /* See above block comment. */ /* * Recheck ->n_barrier_done to see if others did our work for us. * This means checking ->n_barrier_done for an even-to-odd-to-even * transition. The "if" expression below therefore rounds the old * value up to the next even number and adds two before comparing. */ snap_done = ACCESS_ONCE(rsp->n_barrier_done); _rcu_barrier_trace(rsp, "Check", -1, snap_done); if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) { _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done); smp_mb(); /* caller's subsequent code after above check. */ mutex_unlock(&rsp->barrier_mutex); return; } /* * Increment ->n_barrier_done to avoid duplicate work. Use * ACCESS_ONCE() to prevent the compiler from speculating * the increment to precede the early-exit check. */ ACCESS_ONCE(rsp->n_barrier_done)++; WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1); _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done); smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */ /* * Initialize the count to one rather than to zero in order to * avoid a too-soon return to zero in case of a short grace period * (or preemption of this task). Also flag this task as doing * an rcu_barrier(). This will prevent anyone else from adopting * orphaned callbacks, which could cause otherwise failure if a * CPU went offline and quickly came back online. To see this, * consider the following sequence of events: * * 1. We cause CPU 0 to post an rcu_barrier_callback() callback. * 2. CPU 1 goes offline, orphaning its callbacks. * 3. CPU 0 adopts CPU 1's orphaned callbacks. * 4. CPU 1 comes back online. * 5. We cause CPU 1 to post an rcu_barrier_callback() callback. * 6. Both rcu_barrier_callback() callbacks are invoked, awakening * us -- but before CPU 1's orphaned callbacks are invoked!!! */ init_completion(&rsp->barrier_completion); atomic_set(&rsp->barrier_cpu_count, 1); raw_spin_lock_irqsave(&rsp->onofflock, flags); rsp->rcu_barrier_in_progress = current; raw_spin_unlock_irqrestore(&rsp->onofflock, flags); /* * Force every CPU with callbacks to register a new callback * that will tell us when all the preceding callbacks have * been invoked. If an offline CPU has callbacks, wait for * it to either come back online or to finish orphaning those * callbacks. */ for_each_possible_cpu(cpu) { preempt_disable(); rdp = per_cpu_ptr(rsp->rda, cpu); if (cpu_is_offline(cpu)) { _rcu_barrier_trace(rsp, "Offline", cpu, rsp->n_barrier_done); preempt_enable(); while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen)) schedule_timeout_interruptible(1); } else if (ACCESS_ONCE(rdp->qlen)) { _rcu_barrier_trace(rsp, "OnlineQ", cpu, rsp->n_barrier_done); smp_call_function_single(cpu, rcu_barrier_func, rsp, 1); preempt_enable(); } else { _rcu_barrier_trace(rsp, "OnlineNQ", cpu, rsp->n_barrier_done); preempt_enable(); } } /* * Now that all online CPUs have rcu_barrier_callback() callbacks * posted, we can adopt all of the orphaned callbacks and place * an rcu_barrier_callback() callback after them. When that is done, * we are guaranteed to have an rcu_barrier_callback() callback * following every callback that could possibly have been * registered before _rcu_barrier() was called. */ raw_spin_lock_irqsave(&rsp->onofflock, flags); rcu_adopt_orphan_cbs(rsp); rsp->rcu_barrier_in_progress = NULL; raw_spin_unlock_irqrestore(&rsp->onofflock, flags); atomic_inc(&rsp->barrier_cpu_count); smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */ rd.rsp = rsp; rsp->call(&rd.barrier_head, rcu_barrier_callback); /* * Now that we have an rcu_barrier_callback() callback on each * CPU, and thus each counted, remove the initial count. */ if (atomic_dec_and_test(&rsp->barrier_cpu_count)) complete(&rsp->barrier_completion); /* Increment ->n_barrier_done to prevent duplicate work. */ smp_mb(); /* Keep increment after above mechanism. */ ACCESS_ONCE(rsp->n_barrier_done)++; WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0); _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done); smp_mb(); /* Keep increment before caller's subsequent code. */ /* Wait for all rcu_barrier_callback() callbacks to be invoked. */ wait_for_completion(&rsp->barrier_completion); /* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rsp->barrier_mutex); destroy_rcu_head_on_stack(&rd.barrier_head); } /** * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete. */ void rcu_barrier_bh(void) { _rcu_barrier(&rcu_bh_state); } EXPORT_SYMBOL_GPL(rcu_barrier_bh); /** * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks. */ void rcu_barrier_sched(void) { _rcu_barrier(&rcu_sched_state); } EXPORT_SYMBOL_GPL(rcu_barrier_sched); /* * Do boot-time initialization of a CPU's per-CPU RCU data. */ static void __init rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) { unsigned long flags; int i; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo); rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; rdp->qlen_lazy = 0; rdp->qlen = 0; rdp->dynticks = &per_cpu(rcu_dynticks, cpu); WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE); WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1); rdp->cpu = cpu; rdp->rsp = rsp; raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * Initialize a CPU's per-CPU RCU data. Note that only one online or * offline event can be happening at a given time. Note also that we * can accept some slop in the rsp->completed access due to the fact * that this CPU cannot possibly have any RCU callbacks in flight yet. */ static void __cpuinit rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) { unsigned long flags; unsigned long mask; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); rdp->beenonline = 1; /* We have now been online. */ rdp->preemptible = preemptible; rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; atomic_set(&rdp->dynticks->dynticks, (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); rcu_prepare_for_idle_init(cpu); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ /* * A new grace period might start here. If so, we won't be part * of it, but that is OK, as we are currently in a quiescent state. */ /* Exclude any attempts to start a new GP on large systems. */ raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ /* Add CPU to rcu_node bitmasks. */ rnp = rdp->mynode; mask = rdp->grpmask; do { /* Exclude any attempts to start a new GP on small systems. */ raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rnp->qsmaskinit |= mask; mask = rnp->grpmask; if (rnp == rdp->mynode) { /* * If there is a grace period in progress, we will * set up to wait for it next time we run the * RCU core code. */ rdp->gpnum = rnp->completed; rdp->completed = rnp->completed; rdp->passed_quiesce = 0; rdp->qs_pending = 0; rdp->passed_quiesce_gpnum = rnp->gpnum - 1; trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl"); } raw_spin_unlock(&rnp->lock); /* irqs already disabled. */ rnp = rnp->parent; } while (rnp != NULL && !(rnp->qsmaskinit & mask)); raw_spin_unlock_irqrestore(&rsp->onofflock, flags); } static void __cpuinit rcu_prepare_cpu(int cpu) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) rcu_init_percpu_data(cpu, rsp, strcmp(rsp->name, "rcu_preempt") == 0); } /* * Handle CPU online/offline notification events. */ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { long cpu = (long)hcpu; struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); struct rcu_node *rnp = rdp->mynode; struct rcu_state *rsp; trace_rcu_utilization("Start CPU hotplug"); switch (action) { case CPU_UP_PREPARE: case CPU_UP_PREPARE_FROZEN: rcu_prepare_cpu(cpu); rcu_prepare_kthreads(cpu); break; case CPU_ONLINE: case CPU_DOWN_FAILED: rcu_node_kthread_setaffinity(rnp, -1); rcu_cpu_kthread_setrt(cpu, 1); break; case CPU_DOWN_PREPARE: rcu_node_kthread_setaffinity(rnp, cpu); rcu_cpu_kthread_setrt(cpu, 0); break; case CPU_DYING: case CPU_DYING_FROZEN: /* * The whole machine is "stopped" except this CPU, so we can * touch any data without introducing corruption. We send the * dying CPU's callbacks to an arbitrarily chosen online CPU. */ for_each_rcu_flavor(rsp) rcu_cleanup_dying_cpu(rsp); rcu_cleanup_after_idle(cpu); break; case CPU_DEAD: case CPU_DEAD_FROZEN: case CPU_UP_CANCELED: case CPU_UP_CANCELED_FROZEN: for_each_rcu_flavor(rsp) rcu_cleanup_dead_cpu(cpu, rsp); break; default: break; } trace_rcu_utilization("End CPU hotplug"); return NOTIFY_OK; } /* * This function is invoked towards the end of the scheduler's initialization * process. Before this is called, the idle task might contain * RCU read-side critical sections (during which time, this idle * task is booting the system). After this function is called, the * idle tasks are prohibited from containing RCU read-side critical * sections. This function also enables RCU lockdep checking. */ void rcu_scheduler_starting(void) { WARN_ON(num_online_cpus() != 1); WARN_ON(nr_context_switches() > 0); rcu_scheduler_active = 1; } /* * Compute the per-level fanout, either using the exact fanout specified * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT. */ #ifdef CONFIG_RCU_FANOUT_EXACT static void __init rcu_init_levelspread(struct rcu_state *rsp) { int i; for (i = rcu_num_lvls - 1; i > 0; i--) rsp->levelspread[i] = CONFIG_RCU_FANOUT; rsp->levelspread[0] = rcu_fanout_leaf; } #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */ static void __init rcu_init_levelspread(struct rcu_state *rsp) { int ccur; int cprv; int i; cprv = NR_CPUS; for (i = rcu_num_lvls - 1; i >= 0; i--) { ccur = rsp->levelcnt[i]; rsp->levelspread[i] = (cprv + ccur - 1) / ccur; cprv = ccur; } } #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */ /* * Helper function for rcu_init() that initializes one rcu_state structure. */ static void __init rcu_init_one(struct rcu_state *rsp, struct rcu_data __percpu *rda) { static char *buf[] = { "rcu_node_level_0", "rcu_node_level_1", "rcu_node_level_2", "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */ int cpustride = 1; int i; int j; struct rcu_node *rnp; BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */ /* Initialize the level-tracking arrays. */ for (i = 0; i < rcu_num_lvls; i++) rsp->levelcnt[i] = num_rcu_lvl[i]; for (i = 1; i < rcu_num_lvls; i++) rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1]; rcu_init_levelspread(rsp); /* Initialize the elements themselves, starting from the leaves. */ for (i = rcu_num_lvls - 1; i >= 0; i--) { cpustride *= rsp->levelspread[i]; rnp = rsp->level[i]; for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) { raw_spin_lock_init(&rnp->lock); lockdep_set_class_and_name(&rnp->lock, &rcu_node_class[i], buf[i]); rnp->gpnum = 0; rnp->qsmask = 0; rnp->qsmaskinit = 0; rnp->grplo = j * cpustride; rnp->grphi = (j + 1) * cpustride - 1; if (rnp->grphi >= NR_CPUS) rnp->grphi = NR_CPUS - 1; if (i == 0) { rnp->grpnum = 0; rnp->grpmask = 0; rnp->parent = NULL; } else { rnp->grpnum = j % rsp->levelspread[i - 1]; rnp->grpmask = 1UL << rnp->grpnum; rnp->parent = rsp->level[i - 1] + j / rsp->levelspread[i - 1]; } rnp->level = i; INIT_LIST_HEAD(&rnp->blkd_tasks); } } rsp->rda = rda; rnp = rsp->level[rcu_num_lvls - 1]; for_each_possible_cpu(i) { while (i > rnp->grphi) rnp++; per_cpu_ptr(rsp->rda, i)->mynode = rnp; rcu_boot_init_percpu_data(i, rsp); } list_add(&rsp->flavors, &rcu_struct_flavors); } /* * Compute the rcu_node tree geometry from kernel parameters. This cannot * replace the definitions in rcutree.h because those are needed to size * the ->node array in the rcu_state structure. */ static void __init rcu_init_geometry(void) { int i; int j; int n = nr_cpu_ids; int rcu_capacity[MAX_RCU_LVLS + 1]; /* If the compile-time values are accurate, just leave. */ if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF) return; /* * Compute number of nodes that can be handled an rcu_node tree * with the given number of levels. Setting rcu_capacity[0] makes * some of the arithmetic easier. */ rcu_capacity[0] = 1; rcu_capacity[1] = rcu_fanout_leaf; for (i = 2; i <= MAX_RCU_LVLS; i++) rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT; /* * The boot-time rcu_fanout_leaf parameter is only permitted * to increase the leaf-level fanout, not decrease it. Of course, * the leaf-level fanout cannot exceed the number of bits in * the rcu_node masks. Finally, the tree must be able to accommodate * the configured number of CPUs. Complain and fall back to the * compile-time values if these limits are exceeded. */ if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF || rcu_fanout_leaf > sizeof(unsigned long) * 8 || n > rcu_capacity[MAX_RCU_LVLS]) { WARN_ON(1); return; } /* Calculate the number of rcu_nodes at each level of the tree. */ for (i = 1; i <= MAX_RCU_LVLS; i++) if (n <= rcu_capacity[i]) { for (j = 0; j <= i; j++) num_rcu_lvl[j] = DIV_ROUND_UP(n, rcu_capacity[i - j]); rcu_num_lvls = i; for (j = i + 1; j <= MAX_RCU_LVLS; j++) num_rcu_lvl[j] = 0; break; } /* Calculate the total number of rcu_node structures. */ rcu_num_nodes = 0; for (i = 0; i <= MAX_RCU_LVLS; i++) rcu_num_nodes += num_rcu_lvl[i]; rcu_num_nodes -= n; } void __init rcu_init(void) { int cpu; rcu_bootup_announce(); rcu_init_geometry(); rcu_init_one(&rcu_sched_state, &rcu_sched_data); rcu_init_one(&rcu_bh_state, &rcu_bh_data); __rcu_init_preempt(); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); /* * We don't need protection against CPU-hotplug here because * this is called early in boot, before either interrupts * or the scheduler are operational. */ cpu_notifier(rcu_cpu_notify, 0); for_each_online_cpu(cpu) rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu); check_cpu_stall_init(); } #include "rcutree_plugin.h"