/* * 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 #ifdef CONFIG_DEBUG_LOCK_ALLOC static struct lock_class_key rcu_lock_key; struct lockdep_map rcu_lock_map = STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); EXPORT_SYMBOL_GPL(rcu_lock_map); #endif /* Data structures. */ #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, /* == MAX_RCU_LVLS */ \ }, \ .signaled = RCU_SIGNAL_INIT, \ .gpnum = -300, \ .completed = -300, \ .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \ .fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \ .n_force_qs = 0, \ .n_force_qs_ngp = 0, \ } struct rcu_state rcu_state = RCU_STATE_INITIALIZER(rcu_state); DEFINE_PER_CPU(struct rcu_data, rcu_data); struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); /* * Increment the quiescent state counter. * The counter is a bit degenerated: 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. Thus just a flag. */ void rcu_qsctr_inc(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_data, cpu); rdp->passed_quiesc = 1; rdp->passed_quiesc_completed = rdp->completed; } void rcu_bh_qsctr_inc(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); rdp->passed_quiesc = 1; rdp->passed_quiesc_completed = rdp->completed; } #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. */ static void force_quiescent_state(struct rcu_state *rsp, int relaxed); /* * Return the number of RCU batches processed thus far for debug & stats. */ long rcu_batches_completed(void) { return rcu_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * 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) { /* ACCESS_ONCE() because we are accessing outside of lock. */ return *rdp->nxttail[RCU_DONE_TAIL] && ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum); } /* * 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; } /* 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 static DEFINE_RATELIMIT_STATE(rcu_rs, 10 * HZ, 5); /** * 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_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs); 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_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs); 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_RATELIMIT(!(rdtp->dynticks_nmi & 0x1), &rcu_rs); 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_RATELIMIT(rdtp->dynticks_nmi & 0x1, &rcu_rs); } /** * 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_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs); 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_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs); /* If the interrupt queued a callback, get out of dyntick mode. */ if (__get_cpu_var(rcu_data).nxtlist || __get_cpu_var(rcu_bh_data).nxtlist) set_need_resched(); } /* * Record the specified "completed" value, which is later used to validate * dynticks counter manipulations. Specify "rsp->completed - 1" to * unconditionally invalidate any future dynticks manipulations (which is * useful at the beginning of a grace period). */ static void dyntick_record_completed(struct rcu_state *rsp, long comp) { rsp->dynticks_completed = comp; } #ifdef CONFIG_SMP /* * Recall the previously recorded value of the completion for dynticks. */ static long dyntick_recall_completed(struct rcu_state *rsp) { return rsp->dynticks_completed; } /* * 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 already in a quiescent state courtesy of dynticks idle mode. */ 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 */ static void dyntick_record_completed(struct rcu_state *rsp, long comp) { } #ifdef CONFIG_SMP /* * If there are no dynticks, then the only way that a CPU can passively * be in a quiescent state is to be offline. Unlike dynticks idle, which * is a point in time during the prior (already finished) grace period, * an offline CPU is always in a quiescent state, and thus can be * unconditionally applied. So just return the current value of completed. */ static long dyntick_recall_completed(struct rcu_state *rsp) { return rsp->completed; } 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); struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1]; struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES]; /* Only let one CPU complain about others per time interval. */ spin_lock_irqsave(&rnp->lock, flags); delta = jiffies - rsp->jiffies_stall; if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum == rsp->completed) { spin_unlock_irqrestore(&rnp->lock, flags); return; } rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; spin_unlock_irqrestore(&rnp->lock, flags); /* OK, time to rat on our buddy... */ printk(KERN_ERR "INFO: RCU detected CPU stalls:"); for (; rnp_cur < rnp_end; rnp_cur++) { if (rnp_cur->qsmask == 0) continue; for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++) if (rnp_cur->qsmask & (1UL << cpu)) printk(" %d", rnp_cur->grplo + cpu); } printk(" (detected by %d, t=%ld jiffies)\n", smp_processor_id(), (long)(jiffies - rsp->gp_start)); 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); dump_stack(); spin_lock_irqsave(&rnp->lock, flags); if ((long)(jiffies - rsp->jiffies_stall) >= 0) rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; 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 (rsp->gpnum != rsp->completed && 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. */ static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp) { rdp->qs_pending = 1; rdp->passed_quiesc = 0; rdp->gpnum = rsp->gpnum; } /* * 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; } /* * 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); struct rcu_node *rnp_cur; struct rcu_node *rnp_end; if (!cpu_needs_another_gp(rsp, rdp)) { spin_unlock_irqrestore(&rnp->lock, flags); return; } /* Advance to a new grace period and initialize state. */ rsp->gpnum++; 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); dyntick_record_completed(rsp, rsp->completed - 1); note_new_gpnum(rsp, rdp); /* * Because we are first, we know that all our callbacks will * be covered by this upcoming grace period, even the ones * that were registered arbitrarily recently. */ rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; /* Special-case the common single-level case. */ if (NUM_RCU_NODES == 1) { rnp->qsmask = rnp->qsmaskinit; rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ spin_unlock_irqrestore(&rnp->lock, flags); return; } spin_unlock(&rnp->lock); /* leave irqs disabled. */ /* Exclude any concurrent CPU-hotplug operations. */ spin_lock(&rsp->onofflock); /* irqs already disabled. */ /* * Set the quiescent-state-needed bits in all the non-leaf RCU * nodes for all currently online CPUs. 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. In addition, we have excluded CPU-hotplug operations. * * We therefore do not need to hold any locks. Any required * memory barriers will be supplied by the locks guarding the * leaf rcu_nodes in the hierarchy. */ rnp_end = rsp->level[NUM_RCU_LVLS - 1]; for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) rnp_cur->qsmask = rnp_cur->qsmaskinit; /* * Now set up the leaf nodes. Here we must be careful. First, * we need to hold the lock in order to exclude other CPUs, which * might be contending for the leaf nodes' locks. Second, as * soon as we initialize a given leaf node, its CPUs might run * up the rest of the hierarchy. We must therefore acquire locks * for each node that we touch during this stage. (But we still * are excluding 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. */ rnp_end = &rsp->node[NUM_RCU_NODES]; rnp_cur = rsp->level[NUM_RCU_LVLS - 1]; for (; rnp_cur < rnp_end; rnp_cur++) { spin_lock(&rnp_cur->lock); /* irqs already disabled. */ rnp_cur->qsmask = rnp_cur->qsmaskinit; spin_unlock(&rnp_cur->lock); /* irqs already disabled. */ } rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */ spin_unlock_irqrestore(&rsp->onofflock, flags); } /* * 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) { long completed_snap; unsigned long flags; local_irq_save(flags); completed_snap = ACCESS_ONCE(rsp->completed); /* outside of lock. */ /* Did another grace period end? */ if (rdp->completed != completed_snap) { /* 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 = completed_snap; } local_irq_restore(flags); } /* * Similar to cpu_quiet(), for which it is a helper function. Allows * a group of CPUs to be quieted at one go, though all the CPUs in the * group must be represented by the same leaf rcu_node structure. * That structure's lock must be held upon entry, and it is released * before return. */ static void cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { /* Walk up the rcu_node hierarchy. */ for (;;) { if (!(rnp->qsmask & mask)) { /* Our bit has already been cleared, so done. */ spin_unlock_irqrestore(&rnp->lock, flags); return; } rnp->qsmask &= ~mask; if (rnp->qsmask != 0) { /* Other bits still set at this level, so done. */ spin_unlock_irqrestore(&rnp->lock, flags); return; } mask = rnp->grpmask; if (rnp->parent == NULL) { /* No more levels. Exit loop holding root lock. */ break; } spin_unlock_irqrestore(&rnp->lock, flags); rnp = rnp->parent; spin_lock_irqsave(&rnp->lock, flags); } /* * Get here if we are the last CPU to pass through a quiescent * state for this grace period. Clean up and let rcu_start_gp() * start up the next grace period if one is needed. Note that * we still hold rnp->lock, as required by rcu_start_gp(), which * will release it. */ rsp->completed = rsp->gpnum; rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]); rcu_start_gp(rsp, flags); /* releases rnp->lock. */ } /* * Record a quiescent state for the specified CPU, which must either be * the current CPU or an 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 cpu_quiet(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; spin_lock_irqsave(&rnp->lock, flags); if (lastcomp != ACCESS_ONCE(rsp->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 cpu_quiet_msk() if this race * occurred. */ rdp->passed_quiesc = 0; /* try again later! */ spin_unlock_irqrestore(&rnp->lock, flags); return; } mask = rdp->grpmask; if ((rnp->qsmask & mask) == 0) { 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 = rsp->rda[smp_processor_id()]; rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; cpu_quiet_msk(mask, rsp, rnp, flags); /* releases 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 cpu_quiet() will be the judge of that). */ cpu_quiet(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed); } #ifdef CONFIG_HOTPLUG_CPU /* * 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) { int i; unsigned long flags; long lastcomp; unsigned long mask; struct rcu_data *rdp = rsp->rda[cpu]; struct rcu_data *rdp_me; struct rcu_node *rnp; /* Exclude any attempts to start a new grace period. */ spin_lock_irqsave(&rsp->onofflock, flags); /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */ rnp = rdp->mynode; mask = rdp->grpmask; /* rnp->grplo is constant. */ do { spin_lock(&rnp->lock); /* irqs already disabled. */ rnp->qsmaskinit &= ~mask; if (rnp->qsmaskinit != 0) { spin_unlock(&rnp->lock); /* irqs already disabled. */ break; } mask = rnp->grpmask; spin_unlock(&rnp->lock); /* irqs already disabled. */ rnp = rnp->parent; } while (rnp != NULL); lastcomp = rsp->completed; spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ /* Being offline is a quiescent state, so go record it. */ cpu_quiet(cpu, rsp, rdp, lastcomp); /* * Move callbacks from the outgoing CPU to the running CPU. * Note that the outgoing CPU is now quiscent, so it is now * (uncharacteristically) safe to access it rcu_data structure. * Note also that we must carefully retain the order of the * outgoing CPU's callbacks in order for rcu_barrier() to work * correctly. Finally, note that we start all the callbacks * afresh, even those that have passed through a grace period * and are therefore ready to invoke. The theory is that hotplug * events are rare, and that if they are frequent enough to * indefinitely delay callbacks, you have far worse things to * be worrying about. */ rdp_me = rsp->rda[smp_processor_id()]; if (rdp->nxtlist != NULL) { *rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; rdp_me->qlen += rdp->qlen; rdp->qlen = 0; } local_irq_restore(flags); } /* * 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_state); __rcu_offline_cpu(cpu, &rcu_bh_state); } #else /* #ifdef CONFIG_HOTPLUG_CPU */ 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_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; 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 (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 count it. * * No memory barrier is required here because both * rcu_qsctr_inc() and rcu_bh_qsctr_inc() reference * only CPU-local variables that other CPUs neither * access nor modify, at least not while the corresponding * CPU is online. */ rcu_qsctr_inc(cpu); rcu_bh_qsctr_inc(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 count it. */ rcu_bh_qsctr_inc(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_cur = rsp->level[NUM_RCU_LVLS - 1]; struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES]; for (; rnp_cur < rnp_end; rnp_cur++) { mask = 0; spin_lock_irqsave(&rnp_cur->lock, flags); if (rsp->completed != lastcomp) { spin_unlock_irqrestore(&rnp_cur->lock, flags); return 1; } if (rnp_cur->qsmask == 0) { spin_unlock_irqrestore(&rnp_cur->lock, flags); continue; } cpu = rnp_cur->grplo; bit = 1; for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) { if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu])) mask |= bit; } if (mask != 0 && rsp->completed == lastcomp) { /* cpu_quiet_msk() releases rnp_cur->lock. */ cpu_quiet_msk(mask, rsp, rnp_cur, flags); continue; } spin_unlock_irqrestore(&rnp_cur->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; if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) return; /* No grace period in progress, nothing to force. */ if (!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++; spin_lock(&rnp->lock); lastcomp = rsp->completed; signaled = rsp->signaled; rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; if (lastcomp == rsp->gpnum) { rsp->n_force_qs_ngp++; spin_unlock(&rnp->lock); goto unlock_ret; /* no GP in progress, time updated. */ } spin_unlock(&rnp->lock); switch (signaled) { case RCU_GP_INIT: break; /* grace period still 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; /* Update state, record completion counter. */ spin_lock(&rnp->lock); if (lastcomp == rsp->completed) { rsp->signaled = RCU_FORCE_QS; dyntick_record_completed(rsp, lastcomp); } spin_unlock(&rnp->lock); break; case RCU_FORCE_QS: /* Check dyntick-idle state, send IPI to laggarts. */ if (rcu_process_dyntick(rsp, dyntick_recall_completed(rsp), rcu_implicit_dynticks_qs)) goto unlock_ret; /* Leave state in case more forcing is required. */ break; } unlock_ret: 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; /* * 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)) { 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(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_state, &__get_cpu_var(rcu_data)); __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); /* * 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 (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) { unsigned long nestflag; struct rcu_node *rnp_root = rcu_get_root(rsp); 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. */ if (unlikely(++rdp->qlen > qhimark)) { rdp->blimit = LONG_MAX; force_quiescent_state(rsp, 0); } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0) force_quiescent_state(rsp, 1); local_irq_restore(flags); } /* * Queue an RCU callback for invocation after a grace period. */ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_state); } EXPORT_SYMBOL_GPL(call_rcu); /* * 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); /* * 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) { 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) return 1; /* Does this CPU have callbacks ready to invoke? */ if (cpu_has_callbacks_ready_to_invoke(rdp)) return 1; /* Has RCU gone idle with this CPU needing another grace period? */ if (cpu_needs_another_gp(rsp, rdp)) return 1; /* Has another RCU grace period completed? */ if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */ return 1; /* Has a new RCU grace period started? */ if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */ return 1; /* Has an RCU GP gone long enough to send resched IPIs &c? */ if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) && ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) return 1; /* nothing to do */ 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. */ int rcu_pending(int cpu) { return __rcu_pending(&rcu_state, &per_cpu(rcu_data, cpu)) || __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, 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_data, cpu).nxtlist || per_cpu(rcu_bh_data, cpu).nxtlist; } /* * Initialize a CPU's per-CPU RCU data. We take this "scorched earth" * approach so that we don't have to worry about how long the CPU has * been gone, or whether it ever was online previously. We do trust the * ->mynode field, as it is constant for a given struct rcu_data and * initialized during early boot. * * 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) { unsigned long flags; int i; long lastcomp; 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. */ spin_lock_irqsave(&rnp->lock, flags); lastcomp = rsp->completed; rdp->completed = lastcomp; rdp->gpnum = lastcomp; 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->passed_quiesc_completed = lastcomp - 1; 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; rdp->blimit = blimit; #ifdef CONFIG_NO_HZ rdp->dynticks = &per_cpu(rcu_dynticks, cpu); #endif /* #ifdef CONFIG_NO_HZ */ rdp->cpu = cpu; 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. */ 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. */ spin_lock(&rnp->lock); /* irqs already disabled. */ rnp->qsmaskinit |= mask; mask = rnp->grpmask; spin_unlock(&rnp->lock); /* irqs already disabled. */ rnp = rnp->parent; } while (rnp != NULL && !(rnp->qsmaskinit & mask)); spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ /* * A new grace period might start here. If so, we will be part of * it, and its gpnum will be greater than ours, so we will * participate. It is also possible for the gpnum to have been * incremented before this function was called, and the bitmasks * to not be filled out until now, in which case we will also * participate due to our gpnum being behind. */ /* Since it is coming online, the CPU is in a quiescent state. */ cpu_quiet(cpu, rsp, rdp, lastcomp); local_irq_restore(flags); } static void __cpuinit rcu_online_cpu(int cpu) { rcu_init_percpu_data(cpu, &rcu_state); rcu_init_percpu_data(cpu, &rcu_bh_state); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); } /* * Handle CPU online/offline notifcation 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_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++) { spin_lock_init(&rnp->lock); 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; } } } /* * Helper macro for __rcu_init(). To be used nowhere else! * Assigns leaf node pointers into each CPU's rcu_data structure. */ #define RCU_DATA_PTR_INIT(rsp, rcu_data) \ do { \ 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); \ } \ } while (0) static struct notifier_block __cpuinitdata rcu_nb = { .notifier_call = rcu_cpu_notify, }; void __init __rcu_init(void) { int i; /* All used by RCU_DATA_PTR_INIT(). */ int j; struct rcu_node *rnp; printk(KERN_WARNING "Experimental hierarchical RCU implementation.\n"); #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 */ rcu_init_one(&rcu_state); RCU_DATA_PTR_INIT(&rcu_state, rcu_data); rcu_init_one(&rcu_bh_state); RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data); for_each_online_cpu(i) rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)i); /* Register notifier for non-boot CPUs */ register_cpu_notifier(&rcu_nb); printk(KERN_WARNING "Experimental hierarchical RCU init done.\n"); } module_param(blimit, int, 0); module_param(qhimark, int, 0); module_param(qlowmark, int, 0);