/* * 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 "rcutree.h" /* Data structures. */ static struct lock_class_key rcu_node_class[NUM_RCU_LVLS]; #define RCU_STATE_INITIALIZER(name) { \ .level = { &name.node[0] }, \ .levelcnt = { \ NUM_RCU_LVL_0, /* root of hierarchy. */ \ NUM_RCU_LVL_1, \ NUM_RCU_LVL_2, \ NUM_RCU_LVL_3, \ NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \ }, \ .signaled = RCU_GP_IDLE, \ .gpnum = -300, \ .completed = -300, \ .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&name.onofflock), \ .orphan_cbs_list = NULL, \ .orphan_cbs_tail = &name.orphan_cbs_list, \ .orphan_qlen = 0, \ .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&name.fqslock), \ .n_force_qs = 0, \ .n_force_qs_ngp = 0, \ } struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state); DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); static int rcu_scheduler_active __read_mostly; /* * 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. */ void rcu_sched_qs(int cpu) { struct rcu_data *rdp; rdp = &per_cpu(rcu_sched_data, cpu); rdp->passed_quiesc_completed = rdp->gpnum - 1; barrier(); rdp->passed_quiesc = 1; rcu_preempt_note_context_switch(cpu); } void rcu_bh_qs(int cpu) { struct rcu_data *rdp; rdp = &per_cpu(rcu_bh_data, cpu); rdp->passed_quiesc_completed = rdp->gpnum - 1; barrier(); rdp->passed_quiesc = 1; } #ifdef CONFIG_NO_HZ DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { .dynticks_nesting = 1, .dynticks = 1, }; #endif /* #ifdef CONFIG_NO_HZ */ static int blimit = 10; /* Maximum callbacks per softirq. */ 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); 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); /* * 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]; } #ifdef CONFIG_SMP /* * 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, it is in a quiescent state. We can * trust its state not to change because interrupts are disabled. */ if (cpu_is_offline(rdp->cpu)) { rdp->offline_fqs++; return 1; } /* If preemptable RCU, no point in sending reschedule IPI. */ if (rdp->preemptable) return 0; /* The CPU is online, so send it a reschedule IPI. */ if (rdp->cpu != smp_processor_id()) smp_send_reschedule(rdp->cpu); else set_need_resched(); rdp->resched_ipi++; return 0; } #endif /* #ifdef CONFIG_SMP */ #ifdef CONFIG_NO_HZ /** * rcu_enter_nohz - inform RCU that current CPU is entering nohz * * Enter nohz 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 nohz mode, a possibility * handled by rcu_irq_enter() and rcu_irq_exit()). */ void rcu_enter_nohz(void) { unsigned long flags; struct rcu_dynticks *rdtp; smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */ local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); rdtp->dynticks++; rdtp->dynticks_nesting--; WARN_ON_ONCE(rdtp->dynticks & 0x1); local_irq_restore(flags); } /* * rcu_exit_nohz - inform RCU that current CPU is leaving nohz * * Exit nohz mode, in other words, -enter- the mode in which RCU * read-side critical sections normally occur. */ void rcu_exit_nohz(void) { unsigned long flags; struct rcu_dynticks *rdtp; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); rdtp->dynticks++; rdtp->dynticks_nesting++; WARN_ON_ONCE(!(rdtp->dynticks & 0x1)); local_irq_restore(flags); smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ } /** * 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 & 0x1) return; rdtp->dynticks_nmi++; WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1)); smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ } /** * 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 & 0x1) return; smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */ rdtp->dynticks_nmi++; WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1); } /** * rcu_irq_enter - inform RCU of entry to hard irq context * * If the CPU was idle with dynamic ticks active, this updates the * rdtp->dynticks to let the RCU handling know that the CPU is active. */ void rcu_irq_enter(void) { struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); if (rdtp->dynticks_nesting++) return; rdtp->dynticks++; WARN_ON_ONCE(!(rdtp->dynticks & 0x1)); smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ } /** * rcu_irq_exit - inform RCU of exit from hard irq context * * If the CPU was idle with dynamic ticks active, update the rdp->dynticks * to put let the RCU handling be aware that the CPU is going back to idle * with no ticks. */ void rcu_irq_exit(void) { struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); if (--rdtp->dynticks_nesting) return; smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */ rdtp->dynticks++; WARN_ON_ONCE(rdtp->dynticks & 0x1); /* If the interrupt queued a callback, get out of dyntick mode. */ if (__get_cpu_var(rcu_sched_data).nxtlist || __get_cpu_var(rcu_bh_data).nxtlist) set_need_resched(); } #ifdef CONFIG_SMP /* * 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) { int ret; int snap; int snap_nmi; snap = rdp->dynticks->dynticks; snap_nmi = rdp->dynticks->dynticks_nmi; smp_mb(); /* Order sampling of snap with end of grace period. */ rdp->dynticks_snap = snap; rdp->dynticks_nmi_snap = snap_nmi; ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0); if (ret) rdp->dynticks_fqs++; return ret; } /* * 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) { long curr; long curr_nmi; long snap; long snap_nmi; curr = rdp->dynticks->dynticks; snap = rdp->dynticks_snap; curr_nmi = rdp->dynticks->dynticks_nmi; snap_nmi = rdp->dynticks_nmi_snap; smp_mb(); /* force ordering with cpu entering/leaving dynticks. */ /* * 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 != snap || (curr & 0x1) == 0) && (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) { rdp->dynticks_fqs++; return 1; } /* Go check for the CPU being offline. */ return rcu_implicit_offline_qs(rdp); } #endif /* #ifdef CONFIG_SMP */ #else /* #ifdef CONFIG_NO_HZ */ #ifdef CONFIG_SMP static int dyntick_save_progress_counter(struct rcu_data *rdp) { return 0; } static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) { return rcu_implicit_offline_qs(rdp); } #endif /* #ifdef CONFIG_SMP */ #endif /* #else #ifdef CONFIG_NO_HZ */ #ifdef CONFIG_RCU_CPU_STALL_DETECTOR static void record_gp_stall_check_time(struct rcu_state *rsp) { rsp->gp_start = jiffies; rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK; } static void print_other_cpu_stall(struct rcu_state *rsp) { int cpu; long delta; unsigned long flags; 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 + RCU_SECONDS_TILL_STALL_RECHECK; /* * Now rat on any tasks that got kicked up to the root rcu_node * due to CPU offlining. */ rcu_print_task_stall(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); /* OK, time to rat on our buddy... */ printk(KERN_ERR "INFO: RCU detected CPU stalls:"); rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); 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)) printk(" %d", rnp->grplo + cpu); } printk(" (detected by %d, t=%ld jiffies)\n", smp_processor_id(), (long)(jiffies - rsp->gp_start)); trigger_all_cpu_backtrace(); 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); printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n", smp_processor_id(), jiffies - rsp->gp_start); trigger_all_cpu_backtrace(); raw_spin_lock_irqsave(&rnp->lock, flags); if ((long)(jiffies - rsp->jiffies_stall) >= 0) rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; 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) { long delta; struct rcu_node *rnp; delta = jiffies - rsp->jiffies_stall; rnp = rdp->mynode; if ((rnp->qsmask & rdp->grpmask) && delta >= 0) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) { /* They had two time units to dump stack, so complain. */ print_other_cpu_stall(rsp); } } #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ static void record_gp_stall_check_time(struct rcu_state *rsp) { } static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) { } #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* * 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) { rdp->qs_pending = 1; rdp->passed_quiesc = 0; rdp->gpnum = rnp->gpnum; } } 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, retry 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; } } /* * 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, retry 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. */ static void rcu_start_gp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { struct rcu_data *rdp = rsp->rda[smp_processor_id()]; struct rcu_node *rnp = rcu_get_root(rsp); if (!cpu_needs_another_gp(rsp, rdp)) { if (rnp->completed == rsp->completed) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } 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->completed; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } local_irq_restore(flags); return; } /* Advance to a new grace period and initialize state. */ rsp->gpnum++; WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT); rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); /* Special-case the common single-level case. */ if (NUM_RCU_NODES == 1) { rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; rnp->gpnum = rsp->gpnum; rnp->completed = rsp->completed; rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ rcu_start_gp_per_cpu(rsp, rnp, rdp); raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } 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); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } rnp = rcu_get_root(rsp); raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rsp->signaled = 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) { WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); rsp->completed = rsp->gpnum; rsp->signaled = 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; if (rnp->qsmask != 0 || rcu_preempted_readers(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 lastcomp) { unsigned long flags; unsigned long mask; struct rcu_node *rnp; rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); if (lastcomp != rnp->completed) { /* * Someone beat us to it for this grace period, so leave. * The race with GP start is resolved by the fact that we * hold the leaf rcu_node lock, so that the per-CPU bits * cannot yet be initialized -- so we would simply find our * CPU's bit already cleared in rcu_report_qs_rnp() if this * race occurred. */ rdp->passed_quiesc = 0; /* try again later! */ 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_quiesc) 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_quiesc_completed); } #ifdef CONFIG_HOTPLUG_CPU /* * Move a dying CPU's RCU callbacks to the ->orphan_cbs_list for the * specified flavor of RCU. The callbacks will be adopted by the next * _rcu_barrier() invocation or by the CPU_DEAD notifier, whichever * comes first. Because this is invoked from the CPU_DYING notifier, * irqs are already disabled. */ static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp) { int i; struct rcu_data *rdp = rsp->rda[smp_processor_id()]; if (rdp->nxtlist == NULL) return; /* irqs disabled, so comparison is stable. */ raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ *rsp->orphan_cbs_tail = rdp->nxtlist; rsp->orphan_cbs_tail = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; rsp->orphan_qlen += rdp->qlen; rdp->qlen = 0; raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ } /* * Adopt previously orphaned RCU callbacks. */ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) { unsigned long flags; struct rcu_data *rdp; raw_spin_lock_irqsave(&rsp->onofflock, flags); rdp = rsp->rda[smp_processor_id()]; if (rsp->orphan_cbs_list == NULL) { raw_spin_unlock_irqrestore(&rsp->onofflock, flags); return; } *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_list; rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_tail; rdp->qlen += rsp->orphan_qlen; rsp->orphan_cbs_list = NULL; rsp->orphan_cbs_tail = &rsp->orphan_cbs_list; rsp->orphan_qlen = 0; raw_spin_unlock_irqrestore(&rsp->onofflock, flags); } /* * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy * and move all callbacks from the outgoing CPU to the current one. */ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) { unsigned long flags; unsigned long mask; int need_report = 0; struct rcu_data *rdp = rsp->rda[cpu]; struct rcu_node *rnp; /* Exclude any attempts to start a new grace period. */ raw_spin_lock_irqsave(&rsp->onofflock, flags); /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */ rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */ 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); rcu_adopt_orphan_cbs(rsp); } /* * Remove the specified CPU from the RCU hierarchy and move any pending * callbacks that it might have to the current CPU. This code assumes * that at least one CPU in the system will remain running at all times. * Any attempt to offline -all- CPUs is likely to strand RCU callbacks. */ static void rcu_offline_cpu(int cpu) { __rcu_offline_cpu(cpu, &rcu_sched_state); __rcu_offline_cpu(cpu, &rcu_bh_state); rcu_preempt_offline_cpu(cpu); } #else /* #ifdef CONFIG_HOTPLUG_CPU */ static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp) { } static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) { } static void rcu_offline_cpu(int cpu) { } #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 count; /* If no callbacks are ready, just return.*/ if (!cpu_has_callbacks_ready_to_invoke(rdp)) return; /* * Extract the list of ready callbacks, disabling to prevent * races with call_rcu() from interrupt handlers. */ local_irq_save(flags); list = rdp->nxtlist; rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = NULL; tail = rdp->nxttail[RCU_DONE_TAIL]; for (count = RCU_NEXT_SIZE - 1; count >= 0; count--) if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL]) rdp->nxttail[count] = &rdp->nxtlist; local_irq_restore(flags); /* Invoke callbacks. */ count = 0; while (list) { next = list->next; prefetch(next); list->func(list); list = next; if (++count >= rdp->blimit) break; } local_irq_save(flags); /* Update count, and requeue any remaining callbacks. */ rdp->qlen -= count; if (list != NULL) { *tail = rdp->nxtlist; rdp->nxtlist = list; for (count = 0; count < RCU_NEXT_SIZE; count++) if (&rdp->nxtlist == rdp->nxttail[count]) rdp->nxttail[count] = tail; else break; } /* 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-raise the RCU softirq if there are callbacks remaining. */ if (cpu_has_callbacks_ready_to_invoke(rdp)) raise_softirq(RCU_SOFTIRQ); } /* * 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 the RCU softirq handler. * * This function must be called with hardirqs disabled. 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) { if (!rcu_pending(cpu)) return; /* if nothing for RCU to do. */ if (user || (idle_cpu(cpu) && rcu_scheduler_active && !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) { /* * 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); raise_softirq(RCU_SOFTIRQ); } #ifdef CONFIG_SMP /* * Scan the leaf rcu_node structures, processing dyntick state for any that * have not yet encountered a quiescent state, using the function specified. * Returns 1 if the current grace period ends while scanning (possibly * because we made it end). */ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp, 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 (rnp->completed != lastcomp) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return 1; } if (rnp->qsmask == 0) { raw_spin_unlock_irqrestore(&rnp->lock, flags); continue; } cpu = rnp->grplo; bit = 1; for (; cpu <= rnp->grphi; cpu++, bit <<= 1) { if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu])) mask |= bit; } if (mask != 0 && rnp->completed == lastcomp) { /* rcu_report_qs_rnp() releases rnp->lock. */ rcu_report_qs_rnp(mask, rsp, rnp, flags); continue; } raw_spin_unlock_irqrestore(&rnp->lock, flags); } return 0; } /* * 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; long lastcomp; struct rcu_node *rnp = rcu_get_root(rsp); u8 signaled; u8 forcenow; if (!rcu_gp_in_progress(rsp)) 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! */ return; /* Someone else is already on the job. */ } if (relaxed && (long)(rsp->jiffies_force_qs - jiffies) >= 0) goto unlock_ret; /* no emergency and done recently. */ rsp->n_force_qs++; raw_spin_lock(&rnp->lock); lastcomp = rsp->gpnum - 1; signaled = rsp->signaled; 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); goto unlock_ret; /* no GP in progress, time updated. */ } raw_spin_unlock(&rnp->lock); switch (signaled) { 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. */ /* Record dyntick-idle state. */ if (rcu_process_dyntick(rsp, lastcomp, dyntick_save_progress_counter)) goto unlock_ret; /* fall into next case. */ case RCU_SAVE_COMPLETED: /* Update state, record completion counter. */ forcenow = 0; raw_spin_lock(&rnp->lock); if (lastcomp + 1 == rsp->gpnum && lastcomp == rsp->completed && rsp->signaled == signaled) { rsp->signaled = RCU_FORCE_QS; rsp->completed_fqs = lastcomp; forcenow = signaled == RCU_SAVE_COMPLETED; } raw_spin_unlock(&rnp->lock); if (!forcenow) break; /* fall into next case. */ case RCU_FORCE_QS: /* Check dyntick-idle state, send IPI to laggarts. */ if (rcu_process_dyntick(rsp, rsp->completed_fqs, rcu_implicit_dynticks_qs)) goto unlock_ret; /* Leave state in case more forcing is required. */ break; } unlock_ret: raw_spin_unlock_irqrestore(&rsp->fqslock, flags); } #else /* #ifdef CONFIG_SMP */ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) { set_need_resched(); } #endif /* #else #ifdef CONFIG_SMP */ /* * This does the RCU processing work from softirq context 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, struct rcu_data *rdp) { unsigned long flags; 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 ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0) 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. */ rcu_do_batch(rsp, rdp); } /* * Do softirq processing for the current CPU. */ static void rcu_process_callbacks(struct softirq_action *unused) { /* * Memory references from any prior RCU read-side critical sections * executed by the interrupted code must be seen before any RCU * grace-period manipulations below. */ smp_mb(); /* See above block comment. */ __rcu_process_callbacks(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); rcu_preempt_process_callbacks(); /* * Memory references from any later RCU read-side critical sections * executed by the interrupted code must be seen after any RCU * grace-period manipulations above. */ smp_mb(); /* See above block comment. */ } static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), struct rcu_state *rsp) { unsigned long flags; struct rcu_data *rdp; 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 = rsp->rda[smp_processor_id()]; rcu_process_gp_end(rsp, rdp); check_for_new_grace_period(rsp, rdp); /* Add the callback to our list. */ *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; /* 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); /* releases rnp_root->lock. */ } /* * 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)) { 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 ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0) 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); } EXPORT_SYMBOL_GPL(call_rcu_sched); /* * Queue an RCU 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); } EXPORT_SYMBOL_GPL(call_rcu_bh); /** * 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) { struct rcu_synchronize rcu; if (rcu_blocking_is_gp()) return; init_completion(&rcu.completion); /* Will wake me after RCU finished. */ call_rcu_sched(&rcu.head, wakeme_after_rcu); /* Wait for it. */ wait_for_completion(&rcu.completion); } 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) { struct rcu_synchronize rcu; if (rcu_blocking_is_gp()) return; init_completion(&rcu.completion); /* Will wake me after RCU finished. */ call_rcu_bh(&rcu.head, wakeme_after_rcu); /* Wait for it. */ wait_for_completion(&rcu.completion); } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); /* * 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 (rdp->qs_pending) { rdp->n_rp_qs_pending++; 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) && ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) { 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) { return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) || __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) || rcu_preempt_pending(cpu); } /* * 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. */ int rcu_needs_cpu(int cpu) { /* RCU callbacks either ready or pending? */ return per_cpu(rcu_sched_data, cpu).nxtlist || per_cpu(rcu_bh_data, cpu).nxtlist || rcu_preempt_needs_cpu(cpu); } /* * 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. */ void rcu_scheduler_starting(void) { WARN_ON(num_online_cpus() != 1); WARN_ON(nr_context_switches() > 0); rcu_scheduler_active = 1; } static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL}; static atomic_t rcu_barrier_cpu_count; static DEFINE_MUTEX(rcu_barrier_mutex); static struct completion rcu_barrier_completion; static void rcu_barrier_callback(struct rcu_head *notused) { if (atomic_dec_and_test(&rcu_barrier_cpu_count)) complete(&rcu_barrier_completion); } /* * Called with preemption disabled, and from cross-cpu IRQ context. */ static void rcu_barrier_func(void *type) { int cpu = smp_processor_id(); struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu); void (*call_rcu_func)(struct rcu_head *head, void (*func)(struct rcu_head *head)); atomic_inc(&rcu_barrier_cpu_count); call_rcu_func = type; call_rcu_func(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, void (*call_rcu_func)(struct rcu_head *head, void (*func)(struct rcu_head *head))) { BUG_ON(in_interrupt()); /* Take mutex to serialize concurrent rcu_barrier() requests. */ mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); /* * Initialize rcu_barrier_cpu_count to 1, then invoke * rcu_barrier_func() on each CPU, so that each CPU also has * incremented rcu_barrier_cpu_count. Only then is it safe to * decrement rcu_barrier_cpu_count -- otherwise the first CPU * might complete its grace period before all of the other CPUs * did their increment, causing this function to return too * early. */ atomic_set(&rcu_barrier_cpu_count, 1); preempt_disable(); /* stop CPU_DYING from filling orphan_cbs_list */ rcu_adopt_orphan_cbs(rsp); on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1); preempt_enable(); /* CPU_DYING can again fill orphan_cbs_list */ if (atomic_dec_and_test(&rcu_barrier_cpu_count)) complete(&rcu_barrier_completion); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); } /** * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete. */ void rcu_barrier_bh(void) { _rcu_barrier(&rcu_bh_state, call_rcu_bh); } 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, call_rcu_sched); } 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 = 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 = 0; #ifdef CONFIG_NO_HZ rdp->dynticks = &per_cpu(rcu_dynticks, cpu); #endif /* #ifdef CONFIG_NO_HZ */ rdp->cpu = cpu; 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 preemptable) { unsigned long flags; unsigned long mask; struct rcu_data *rdp = 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->passed_quiesc = 0; /* We could be racing with new GP, */ rdp->qs_pending = 1; /* so set up to respond to current GP. */ rdp->beenonline = 1; /* We have now been online. */ rdp->preemptable = preemptable; rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; 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) { rdp->gpnum = rnp->completed; /* if GP in progress... */ rdp->completed = rnp->completed; rdp->passed_quiesc_completed = rnp->completed - 1; } 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_online_cpu(int cpu) { rcu_init_percpu_data(cpu, &rcu_sched_state, 0); rcu_init_percpu_data(cpu, &rcu_bh_state, 0); rcu_preempt_init_percpu_data(cpu); } /* * 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; switch (action) { case CPU_UP_PREPARE: case CPU_UP_PREPARE_FROZEN: rcu_online_cpu(cpu); break; case CPU_DYING: case CPU_DYING_FROZEN: /* * preempt_disable() in _rcu_barrier() prevents stop_machine(), * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);" * returns, all online cpus have queued rcu_barrier_func(). * The dying CPU clears its cpu_online_mask bit and * moves all of its RCU callbacks to ->orphan_cbs_list * in the context of stop_machine(), so subsequent calls * to _rcu_barrier() will adopt these callbacks and only * then queue rcu_barrier_func() on all remaining CPUs. */ rcu_send_cbs_to_orphanage(&rcu_bh_state); rcu_send_cbs_to_orphanage(&rcu_sched_state); rcu_preempt_send_cbs_to_orphanage(); break; case CPU_DEAD: case CPU_DEAD_FROZEN: case CPU_UP_CANCELED: case CPU_UP_CANCELED_FROZEN: rcu_offline_cpu(cpu); break; default: break; } return NOTIFY_OK; } /* * 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 = NUM_RCU_LVLS - 1; i >= 0; i--) rsp->levelspread[i] = CONFIG_RCU_FANOUT; } #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 = NUM_RCU_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) { int cpustride = 1; int i; int j; struct rcu_node *rnp; /* Initialize the level-tracking arrays. */ for (i = 1; i < NUM_RCU_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 = NUM_RCU_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(&rnp->lock, &rcu_node_class[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->blocked_tasks[0]); INIT_LIST_HEAD(&rnp->blocked_tasks[1]); INIT_LIST_HEAD(&rnp->blocked_tasks[2]); INIT_LIST_HEAD(&rnp->blocked_tasks[3]); } } } /* * Helper macro for __rcu_init() and __rcu_init_preempt(). To be used * nowhere else! Assigns leaf node pointers into each CPU's rcu_data * structure. */ #define RCU_INIT_FLAVOR(rsp, rcu_data) \ do { \ int i; \ int j; \ struct rcu_node *rnp; \ \ rcu_init_one(rsp); \ rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \ j = 0; \ for_each_possible_cpu(i) { \ if (i > rnp[j].grphi) \ j++; \ per_cpu(rcu_data, i).mynode = &rnp[j]; \ (rsp)->rda[i] = &per_cpu(rcu_data, i); \ rcu_boot_init_percpu_data(i, rsp); \ } \ } while (0) void __init rcu_init(void) { int i; rcu_bootup_announce(); #ifdef CONFIG_RCU_CPU_STALL_DETECTOR printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n"); #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ #if NUM_RCU_LVL_4 != 0 printk(KERN_INFO "Experimental four-level hierarchy is enabled.\n"); #endif /* #if NUM_RCU_LVL_4 != 0 */ RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data); RCU_INIT_FLAVOR(&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(i) rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)i); } #include "rcutree_plugin.h"