exp.2015.10.07a: Reduce OS jitter of RCU-sched expedited grace periods.
fixes.2015.10.06a: Miscellaneous fixes.
static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_exp_class[RCU_NUM_LVLS];
- static struct lock_class_key rcu_exp_sched_class[RCU_NUM_LVLS];
/*
* In order to export the rcu_state name to the tracing tools, it
.level = { &sname##_state.node[0] }, \
.rda = &sname##_data, \
.call = cr, \
- .fqs_state = RCU_GP_IDLE, \
+ .gp_state = RCU_GP_IDLE, \
.gpnum = 0UL - 300UL, \
.completed = 0UL - 300UL, \
.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
+ static void rcu_report_exp_rdp(struct rcu_state *rsp,
+ struct rcu_data *rdp, bool wake);
/* rcuc/rcub kthread realtime priority */
#ifdef CONFIG_RCU_KTHREAD_PRIO
*/
void rcu_sched_qs(void)
{
- if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {
+ unsigned long flags;
+
+ if (__this_cpu_read(rcu_sched_data.cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_sched"),
__this_cpu_read(rcu_sched_data.gpnum),
TPS("cpuqs"));
- __this_cpu_write(rcu_sched_data.passed_quiesce, 1);
+ __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
+ if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
+ return;
+ local_irq_save(flags);
+ if (__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) {
+ __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
+ rcu_report_exp_rdp(&rcu_sched_state,
+ this_cpu_ptr(&rcu_sched_data),
+ true);
+ }
+ local_irq_restore(flags);
}
}
void rcu_bh_qs(void)
{
- if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {
+ if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_bh"),
__this_cpu_read(rcu_bh_data.gpnum),
TPS("cpuqs"));
- __this_cpu_write(rcu_bh_data.passed_quiesce, 1);
+ __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
}
}
*/
void rcu_note_context_switch(void)
{
+ barrier(); /* Avoid RCU read-side critical sections leaking down. */
trace_rcu_utilization(TPS("Start context switch"));
rcu_sched_qs();
rcu_preempt_note_context_switch();
if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
rcu_momentary_dyntick_idle();
trace_rcu_utilization(TPS("End context switch"));
+ barrier(); /* Avoid RCU read-side critical sections leaking up. */
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
* RCU flavors in desperate need of a quiescent state, which will normally
* be none of them). Either way, do a lightweight quiescent state for
* all RCU flavors.
+ *
+ * The barrier() calls are redundant in the common case when this is
+ * called externally, but just in case this is called from within this
+ * file.
+ *
*/
void rcu_all_qs(void)
{
+ barrier(); /* Avoid RCU read-side critical sections leaking down. */
if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
rcu_momentary_dyntick_idle();
this_cpu_inc(rcu_qs_ctr);
+ barrier(); /* Avoid RCU read-side critical sections leaking up. */
}
EXPORT_SYMBOL_GPL(rcu_all_qs);
*/
rdp->gpnum = rnp->gpnum;
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
- rdp->passed_quiesce = 0;
+ rdp->cpu_no_qs.b.norm = true;
rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
- rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
+ rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
zero_cpu_stall_ticks(rdp);
WRITE_ONCE(rdp->gpwrap, false);
}
/*
* Do one round of quiescent-state forcing.
*/
-static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
+static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
{
- int fqs_state = fqs_state_in;
bool isidle = false;
unsigned long maxj;
struct rcu_node *rnp = rcu_get_root(rsp);
WRITE_ONCE(rsp->gp_activity, jiffies);
rsp->n_force_qs++;
- if (fqs_state == RCU_SAVE_DYNTICK) {
+ if (first_time) {
/* Collect dyntick-idle snapshots. */
if (is_sysidle_rcu_state(rsp)) {
isidle = true;
force_qs_rnp(rsp, dyntick_save_progress_counter,
&isidle, &maxj);
rcu_sysidle_report_gp(rsp, isidle, maxj);
- fqs_state = RCU_FORCE_QS;
} else {
/* Handle dyntick-idle and offline CPUs. */
isidle = true;
READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq(&rnp->lock);
}
- return fqs_state;
}
/*
/* Declare grace period done. */
WRITE_ONCE(rsp->completed, rsp->gpnum);
trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
- rsp->fqs_state = RCU_GP_IDLE;
+ rsp->gp_state = RCU_GP_IDLE;
rdp = this_cpu_ptr(rsp->rda);
/* Advance CBs to reduce false positives below. */
needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
*/
static int __noreturn rcu_gp_kthread(void *arg)
{
- int fqs_state;
+ bool first_gp_fqs;
int gf;
unsigned long j;
int ret;
}
/* Handle quiescent-state forcing. */
- fqs_state = RCU_SAVE_DYNTICK;
+ first_gp_fqs = true;
j = jiffies_till_first_fqs;
if (j > HZ) {
j = HZ;
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsstart"));
- fqs_state = rcu_gp_fqs(rsp, fqs_state);
+ rcu_gp_fqs(rsp, first_gp_fqs);
+ first_gp_fqs = false;
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsend"));
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
smp_mb__after_unlock_lock();
- if ((rdp->passed_quiesce == 0 &&
+ if ((rdp->cpu_no_qs.b.norm &&
rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) ||
rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum ||
rdp->gpwrap) {
* We will instead need a new quiescent state that lies
* within the current grace period.
*/
- rdp->passed_quiesce = 0; /* need qs for new gp. */
+ rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
if ((rnp->qsmask & mask) == 0) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
} else {
- rdp->qs_pending = 0;
+ rdp->core_needs_qs = 0;
/*
* This GP can't end until cpu checks in, so all of our
* 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)
+ if (!rdp->core_needs_qs)
return;
/*
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
- if (!rdp->passed_quiesce &&
+ if (rdp->cpu_no_qs.b.norm &&
rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
return;
* is expected to specify a CPU.
*/
static void
-__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
+__call_rcu(struct rcu_head *head, rcu_callback_t func,
struct rcu_state *rsp, int cpu, bool lazy)
{
unsigned long 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))
+void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, &rcu_sched_state, -1, 0);
}
/*
* Queue an RCU callback for invocation after a quicker grace period.
*/
-void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, &rcu_bh_state, -1, 0);
}
* function may only be called from __kfree_rcu().
*/
void kfree_call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
+ rcu_callback_t func)
{
__call_rcu(head, func, rcu_state_p, -1, 1);
}
return rcu_seq_done(&rsp->expedited_sequence, s);
}
+ /*
+ * Reset the ->expmaskinit values in the rcu_node tree to reflect any
+ * recent CPU-online activity. Note that these masks are not cleared
+ * when CPUs go offline, so they reflect the union of all CPUs that have
+ * ever been online. This means that this function normally takes its
+ * no-work-to-do fastpath.
+ */
+ static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
+ {
+ bool done;
+ unsigned long flags;
+ unsigned long mask;
+ unsigned long oldmask;
+ int ncpus = READ_ONCE(rsp->ncpus);
+ struct rcu_node *rnp;
+ struct rcu_node *rnp_up;
+
+ /* If no new CPUs onlined since last time, nothing to do. */
+ if (likely(ncpus == rsp->ncpus_snap))
+ return;
+ rsp->ncpus_snap = ncpus;
+
+ /*
+ * Each pass through the following loop propagates newly onlined
+ * CPUs for the current rcu_node structure up the rcu_node tree.
+ */
+ rcu_for_each_leaf_node(rsp, rnp) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ if (rnp->expmaskinit == rnp->expmaskinitnext) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ continue; /* No new CPUs, nothing to do. */
+ }
+
+ /* Update this node's mask, track old value for propagation. */
+ oldmask = rnp->expmaskinit;
+ rnp->expmaskinit = rnp->expmaskinitnext;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+ /* If was already nonzero, nothing to propagate. */
+ if (oldmask)
+ continue;
+
+ /* Propagate the new CPU up the tree. */
+ mask = rnp->grpmask;
+ rnp_up = rnp->parent;
+ done = false;
+ while (rnp_up) {
+ raw_spin_lock_irqsave(&rnp_up->lock, flags);
+ smp_mb__after_unlock_lock();
+ if (rnp_up->expmaskinit)
+ done = true;
+ rnp_up->expmaskinit |= mask;
+ raw_spin_unlock_irqrestore(&rnp_up->lock, flags);
+ if (done)
+ break;
+ mask = rnp_up->grpmask;
+ rnp_up = rnp_up->parent;
+ }
+ }
+ }
+
+ /*
+ * Reset the ->expmask values in the rcu_node tree in preparation for
+ * a new expedited grace period.
+ */
+ static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
+ {
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ sync_exp_reset_tree_hotplug(rsp);
+ rcu_for_each_node_breadth_first(rsp, rnp) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ WARN_ON_ONCE(rnp->expmask);
+ rnp->expmask = rnp->expmaskinit;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+ }
+
+ /*
+ * Return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period. Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold the root rcu_node's exp_funnel_mutex.
+ */
+ static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+ {
+ return rnp->exp_tasks == NULL &&
+ READ_ONCE(rnp->expmask) == 0;
+ }
+
+ /*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period. This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree. (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Caller must hold the root rcu_node's exp_funnel_mutex and the
+ * specified rcu_node structure's ->lock.
+ */
+ static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+ bool wake, unsigned long flags)
+ __releases(rnp->lock)
+ {
+ unsigned long mask;
+
+ for (;;) {
+ if (!sync_rcu_preempt_exp_done(rnp)) {
+ if (!rnp->expmask)
+ rcu_initiate_boost(rnp, flags);
+ else
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ break;
+ }
+ if (rnp->parent == NULL) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ if (wake) {
+ smp_mb(); /* EGP done before wake_up(). */
+ wake_up(&rsp->expedited_wq);
+ }
+ break;
+ }
+ mask = rnp->grpmask;
+ raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
+ rnp = rnp->parent;
+ raw_spin_lock(&rnp->lock); /* irqs already disabled */
+ smp_mb__after_unlock_lock();
+ WARN_ON_ONCE(!(rnp->expmask & mask));
+ rnp->expmask &= ~mask;
+ }
+ }
+
+ /*
+ * Report expedited quiescent state for specified node. This is a
+ * lock-acquisition wrapper function for __rcu_report_exp_rnp().
+ *
+ * Caller must hold the root rcu_node's exp_funnel_mutex.
+ */
+ static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
+ struct rcu_node *rnp, bool wake)
+ {
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ __rcu_report_exp_rnp(rsp, rnp, wake, flags);
+ }
+
+ /*
+ * Report expedited quiescent state for multiple CPUs, all covered by the
+ * specified leaf rcu_node structure. Caller must hold the root
+ * rcu_node's exp_funnel_mutex.
+ */
+ static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
+ unsigned long mask, bool wake)
+ {
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ if (!(rnp->expmask & mask)) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return;
+ }
+ rnp->expmask &= ~mask;
+ __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
+ }
+
+ /*
+ * Report expedited quiescent state for specified rcu_data (CPU).
+ * Caller must hold the root rcu_node's exp_funnel_mutex.
+ */
+ static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
+ bool wake)
+ {
+ rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
+ }
+
/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
static bool sync_exp_work_done(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp,
}
/* Invoked on each online non-idle CPU for expedited quiescent state. */
- static int synchronize_sched_expedited_cpu_stop(void *data)
+ static void sync_sched_exp_handler(void *data)
{
- struct rcu_data *rdp = data;
- struct rcu_state *rsp = rdp->rsp;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = data;
- /* We are here: If we are last, do the wakeup. */
- rdp->exp_done = true;
- if (atomic_dec_and_test(&rsp->expedited_need_qs))
- wake_up(&rsp->expedited_wq);
- return 0;
+ rdp = this_cpu_ptr(rsp->rda);
+ rnp = rdp->mynode;
+ if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
+ __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
+ return;
+ __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
+ resched_cpu(smp_processor_id());
+ }
+
+ /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
+ static void sync_sched_exp_online_cleanup(int cpu)
+ {
+ struct rcu_data *rdp;
+ int ret;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = &rcu_sched_state;
+
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ rnp = rdp->mynode;
+ if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
+ return;
+ ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
+ WARN_ON_ONCE(ret);
+ }
+
+ /*
+ * Select the nodes that the upcoming expedited grace period needs
+ * to wait for.
+ */
+ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
+ smp_call_func_t func)
+ {
+ int cpu;
+ unsigned long flags;
+ unsigned long mask;
+ unsigned long mask_ofl_test;
+ unsigned long mask_ofl_ipi;
+ int ret;
+ struct rcu_node *rnp;
+
+ sync_exp_reset_tree(rsp);
+ rcu_for_each_leaf_node(rsp, rnp) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+
+ /* Each pass checks a CPU for identity, offline, and idle. */
+ mask_ofl_test = 0;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+ struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+
+ if (raw_smp_processor_id() == cpu ||
+ !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
+ mask_ofl_test |= rdp->grpmask;
+ }
+ mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
+
+ /*
+ * Need to wait for any blocked tasks as well. Note that
+ * additional blocking tasks will also block the expedited
+ * GP until such time as the ->expmask bits are cleared.
+ */
+ if (rcu_preempt_has_tasks(rnp))
+ rnp->exp_tasks = rnp->blkd_tasks.next;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+ /* IPI the remaining CPUs for expedited quiescent state. */
+ mask = 1;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ if (!(mask_ofl_ipi & mask))
+ continue;
+ retry_ipi:
+ ret = smp_call_function_single(cpu, func, rsp, 0);
+ if (!ret) {
+ mask_ofl_ipi &= ~mask;
+ } else {
+ /* Failed, raced with offline. */
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ if (cpu_online(cpu) &&
+ (rnp->expmask & mask)) {
+ raw_spin_unlock_irqrestore(&rnp->lock,
+ flags);
+ schedule_timeout_uninterruptible(1);
+ if (cpu_online(cpu) &&
+ (rnp->expmask & mask))
+ goto retry_ipi;
+ raw_spin_lock_irqsave(&rnp->lock,
+ flags);
+ }
+ if (!(rnp->expmask & mask))
+ mask_ofl_ipi &= ~mask;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+ }
+ /* Report quiescent states for those that went offline. */
+ mask_ofl_test |= mask_ofl_ipi;
+ if (mask_ofl_test)
+ rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
+ }
}
static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
int cpu;
unsigned long jiffies_stall;
unsigned long jiffies_start;
- struct rcu_data *rdp;
+ unsigned long mask;
+ struct rcu_node *rnp;
+ struct rcu_node *rnp_root = rcu_get_root(rsp);
int ret;
jiffies_stall = rcu_jiffies_till_stall_check();
for (;;) {
ret = wait_event_interruptible_timeout(
rsp->expedited_wq,
- !atomic_read(&rsp->expedited_need_qs),
+ sync_rcu_preempt_exp_done(rnp_root),
jiffies_stall);
if (ret > 0)
return;
if (ret < 0) {
/* Hit a signal, disable CPU stall warnings. */
wait_event(rsp->expedited_wq,
- !atomic_read(&rsp->expedited_need_qs));
+ sync_rcu_preempt_exp_done(rnp_root));
return;
}
- pr_err("INFO: %s detected expedited stalls on CPUs: {",
+ pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
rsp->name);
- for_each_online_cpu(cpu) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
-
- if (rdp->exp_done)
- continue;
- pr_cont(" %d", cpu);
+ rcu_for_each_leaf_node(rsp, rnp) {
+ (void)rcu_print_task_exp_stall(rnp);
+ mask = 1;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ struct rcu_data *rdp;
+
+ if (!(rnp->expmask & mask))
+ continue;
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ pr_cont(" %d-%c%c%c", cpu,
+ "O."[cpu_online(cpu)],
+ "o."[!!(rdp->grpmask & rnp->expmaskinit)],
+ "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
+ }
+ mask <<= 1;
}
pr_cont(" } %lu jiffies s: %lu\n",
jiffies - jiffies_start, rsp->expedited_sequence);
- for_each_online_cpu(cpu) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
-
- if (rdp->exp_done)
- continue;
- dump_cpu_task(cpu);
+ rcu_for_each_leaf_node(rsp, rnp) {
+ mask = 1;
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ if (!(rnp->expmask & mask))
+ continue;
+ dump_cpu_task(cpu);
+ }
}
jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
}
*/
void synchronize_sched_expedited(void)
{
- int cpu;
unsigned long s;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_sched_state;
/* Take a snapshot of the sequence number. */
s = rcu_exp_gp_seq_snap(rsp);
- if (!try_get_online_cpus()) {
- /* CPU hotplug operation in flight, fall back to normal GP. */
- wait_rcu_gp(call_rcu_sched);
- atomic_long_inc(&rsp->expedited_normal);
- return;
- }
- WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
-
rnp = exp_funnel_lock(rsp, s);
- if (rnp == NULL) {
- put_online_cpus();
+ if (rnp == NULL)
return; /* Someone else did our work for us. */
- }
rcu_exp_gp_seq_start(rsp);
-
- /* Stop each CPU that is online, non-idle, and not us. */
- init_waitqueue_head(&rsp->expedited_wq);
- atomic_set(&rsp->expedited_need_qs, 1); /* Extra count avoids race. */
- for_each_online_cpu(cpu) {
- struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
-
- rdp->exp_done = false;
-
- /* Skip our CPU and any idle CPUs. */
- if (raw_smp_processor_id() == cpu ||
- !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
- continue;
- atomic_inc(&rsp->expedited_need_qs);
- stop_one_cpu_nowait(cpu, synchronize_sched_expedited_cpu_stop,
- rdp, &rdp->exp_stop_work);
- }
-
- /* Remove extra count and, if necessary, wait for CPUs to stop. */
- if (!atomic_dec_and_test(&rsp->expedited_need_qs))
- synchronize_sched_expedited_wait(rsp);
+ sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
+ synchronize_sched_expedited_wait(rsp);
rcu_exp_gp_seq_end(rsp);
mutex_unlock(&rnp->exp_funnel_mutex);
-
- put_online_cpus();
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rcu_scheduler_fully_active &&
- rdp->qs_pending && !rdp->passed_quiesce &&
+ rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
- rdp->n_rp_qs_pending++;
- } else if (rdp->qs_pending &&
- (rdp->passed_quiesce ||
+ rdp->n_rp_core_needs_qs++;
+ } else if (rdp->core_needs_qs &&
+ (!rdp->cpu_no_qs.b.norm ||
rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
rdp->n_rp_report_qs++;
return 1;
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
{
- static struct lock_class_key rcu_exp_sched_rdp_class;
unsigned long flags;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rcu_get_root(rsp);
mutex_init(&rdp->exp_funnel_mutex);
rcu_boot_init_nocb_percpu_data(rdp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
- if (rsp == &rcu_sched_state)
- lockdep_set_class_and_name(&rdp->exp_funnel_mutex,
- &rcu_exp_sched_rdp_class,
- "rcu_data_exp_sched");
}
/*
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave(&rnp->lock, flags);
- rdp->beenonline = 1; /* We have now been online. */
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->blimit = blimit;
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
smp_mb__after_unlock_lock();
rnp->qsmaskinitnext |= mask;
+ rnp->expmaskinitnext |= mask;
+ if (!rdp->beenonline)
+ WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
+ rdp->beenonline = true; /* We have now been online. */
rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
rdp->completed = rnp->completed;
- rdp->passed_quiesce = false;
+ rdp->cpu_no_qs.b.norm = true;
rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
- rdp->qs_pending = false;
+ rdp->core_needs_qs = false;
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
break;
case CPU_ONLINE:
case CPU_DOWN_FAILED:
+ sync_sched_exp_online_cleanup(cpu);
rcu_boost_kthread_setaffinity(rnp, -1);
break;
case CPU_DOWN_PREPARE:
rcu_cleanup_dying_cpu(rsp);
break;
case CPU_DYING_IDLE:
+ /* QS for any half-done expedited RCU-sched GP. */
+ preempt_disable();
+ rcu_report_exp_rdp(&rcu_sched_state,
+ this_cpu_ptr(rcu_sched_state.rda), true);
+ preempt_enable();
+
for_each_rcu_flavor(rsp) {
rcu_cleanup_dying_idle_cpu(cpu, rsp);
}
static const char * const buf[] = RCU_NODE_NAME_INIT;
static const char * const fqs[] = RCU_FQS_NAME_INIT;
static const char * const exp[] = RCU_EXP_NAME_INIT;
- static const char * const exp_sched[] = RCU_EXP_SCHED_NAME_INIT;
static u8 fl_mask = 0x1;
int levelcnt[RCU_NUM_LVLS]; /* # nodes in each level. */
INIT_LIST_HEAD(&rnp->blkd_tasks);
rcu_init_one_nocb(rnp);
mutex_init(&rnp->exp_funnel_mutex);
- if (rsp == &rcu_sched_state)
- lockdep_set_class_and_name(
- &rnp->exp_funnel_mutex,
- &rcu_exp_sched_class[i], exp_sched[i]);
- else
- lockdep_set_class_and_name(
- &rnp->exp_funnel_mutex,
- &rcu_exp_class[i], exp[i]);
+ lockdep_set_class_and_name(&rnp->exp_funnel_mutex,
+ &rcu_exp_class[i], exp[i]);
}
}
init_waitqueue_head(&rsp->gp_wq);
+ init_waitqueue_head(&rsp->expedited_wq);
rnp = rsp->level[rcu_num_lvls - 1];
for_each_possible_cpu(i) {
while (i > rnp->grphi)
rcu_fanout_leaf, nr_cpu_ids);
/*
- * The boot-time rcu_fanout_leaf parameter is only permitted
- * to increase the leaf-level fanout, not decrease it. Of course,
- * the leaf-level fanout cannot exceed the number of bits in
- * the rcu_node masks. Complain and fall back to the compile-
- * time values if these limits are exceeded.
+ * The boot-time rcu_fanout_leaf parameter must be at least two
+ * and cannot exceed the number of bits in the rcu_node masks.
+ * Complain and fall back to the compile-time values if this
+ * limit is exceeded.
*/
- if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
+ if (rcu_fanout_leaf < 2 ||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
/*
* The tree must be able to accommodate the configured number of CPUs.
- * If this limit is exceeded than we have a serious problem elsewhere.
+ * If this limit is exceeded, fall back to the compile-time values.
*/
- if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1])
- panic("rcu_init_geometry: rcu_capacity[] is too small");
+ if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
+ rcu_fanout_leaf = RCU_FANOUT_LEAF;
+ WARN_ON(1);
+ return;
+ }
/* Calculate the number of levels in the tree. */
for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
# define RCU_NODE_NAME_INIT { "rcu_node_0" }
# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0" }
# define RCU_EXP_NAME_INIT { "rcu_node_exp_0" }
- # define RCU_EXP_SCHED_NAME_INIT \
- { "rcu_node_exp_sched_0" }
#elif NR_CPUS <= RCU_FANOUT_2
# define RCU_NUM_LVLS 2
# define NUM_RCU_LVL_0 1
# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1" }
# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1" }
# define RCU_EXP_NAME_INIT { "rcu_node_exp_0", "rcu_node_exp_1" }
- # define RCU_EXP_SCHED_NAME_INIT \
- { "rcu_node_exp_sched_0", "rcu_node_exp_sched_1" }
#elif NR_CPUS <= RCU_FANOUT_3
# define RCU_NUM_LVLS 3
# define NUM_RCU_LVL_0 1
# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2" }
# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
# define RCU_EXP_NAME_INIT { "rcu_node_exp_0", "rcu_node_exp_1", "rcu_node_exp_2" }
- # define RCU_EXP_SCHED_NAME_INIT \
- { "rcu_node_exp_sched_0", "rcu_node_exp_sched_1", "rcu_node_exp_sched_2" }
#elif NR_CPUS <= RCU_FANOUT_4
# define RCU_NUM_LVLS 4
# define NUM_RCU_LVL_0 1
# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }
# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
# define RCU_EXP_NAME_INIT { "rcu_node_exp_0", "rcu_node_exp_1", "rcu_node_exp_2", "rcu_node_exp_3" }
- # define RCU_EXP_SCHED_NAME_INIT \
- { "rcu_node_exp_sched_0", "rcu_node_exp_sched_1", "rcu_node_exp_sched_2", "rcu_node_exp_sched_3" }
#else
# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
/* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */
/* structure. */
- unsigned long expmask; /* Groups that have ->blkd_tasks */
- /* elements that need to drain to allow the */
- /* current expedited grace period to */
- /* complete (only for PREEMPT_RCU). */
unsigned long qsmaskinit;
- /* Per-GP initial value for qsmask & expmask. */
+ /* Per-GP initial value for qsmask. */
/* Initialized from ->qsmaskinitnext at the */
/* beginning of each grace period. */
unsigned long qsmaskinitnext;
/* Online CPUs for next grace period. */
+ unsigned long expmask; /* CPUs or groups that need to check in */
+ /* to allow the current expedited GP */
+ /* to complete. */
+ unsigned long expmaskinit;
+ /* Per-GP initial values for expmask. */
+ /* Initialized from ->expmaskinitnext at the */
+ /* beginning of each expedited GP. */
+ unsigned long expmaskinitnext;
+ /* Online CPUs for next expedited GP. */
unsigned long grpmask; /* Mask to apply to parent qsmask. */
/* Only one bit will be set in this mask. */
int grplo; /* lowest-numbered CPU or group here. */
for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
(rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
+ /*
+ * Union to allow "aggregate OR" operation on the need for a quiescent
+ * state by the normal and expedited grace periods.
+ */
+ union rcu_noqs {
+ struct {
+ u8 norm;
+ u8 exp;
+ } b; /* Bits. */
+ u16 s; /* Set of bits, aggregate OR here. */
+ };
+
/* Index values for nxttail array in struct rcu_data. */
#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
/* is aware of having started. */
unsigned long rcu_qs_ctr_snap;/* Snapshot of rcu_qs_ctr to check */
/* for rcu_all_qs() invocations. */
- bool passed_quiesce; /* User-mode/idle loop etc. */
- bool qs_pending; /* Core waits for quiesc state. */
+ union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */
+ bool core_needs_qs; /* Core waits for quiesc state. */
bool beenonline; /* CPU online at least once. */
bool gpwrap; /* Possible gpnum/completed wrap. */
struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
/* ticks this CPU has handled */
/* during and after the last grace */
/* period it is aware of. */
- struct cpu_stop_work exp_stop_work;
- /* Expedited grace-period control */
- /* for CPU stopping. */
/* 2) batch handling */
/*
/* 5) __rcu_pending() statistics. */
unsigned long n_rcu_pending; /* rcu_pending() calls since boot. */
- unsigned long n_rp_qs_pending;
+ unsigned long n_rp_core_needs_qs;
unsigned long n_rp_report_qs;
unsigned long n_rp_cb_ready;
unsigned long n_rp_cpu_needs_gp;
struct rcu_head oom_head;
#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
struct mutex exp_funnel_mutex;
- bool exp_done; /* Expedited QS for this CPU? */
/* 7) Callback offloading. */
#ifdef CONFIG_RCU_NOCB_CPU
struct rcu_state *rsp;
};
-/* Values for fqs_state field in struct rcu_state. */
-#define RCU_GP_IDLE 0 /* No grace period in progress. */
-#define RCU_GP_INIT 1 /* Grace period being initialized. */
-#define RCU_SAVE_DYNTICK 2 /* Need to scan dyntick state. */
-#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
-#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
-
/* Values for nocb_defer_wakeup field in struct rcu_data. */
#define RCU_NOGP_WAKE_NOT 0
#define RCU_NOGP_WAKE 1
/* shut bogus gcc warning) */
u8 flavor_mask; /* bit in flavor mask. */
struct rcu_data __percpu *rda; /* pointer of percu rcu_data. */
- void (*call)(struct rcu_head *head, /* call_rcu() flavor. */
- void (*func)(struct rcu_head *head));
+ call_rcu_func_t call; /* call_rcu() flavor. */
+ int ncpus; /* # CPUs seen so far. */
/* The following fields are guarded by the root rcu_node's lock. */
- u8 fqs_state ____cacheline_internodealigned_in_smp;
- /* Force QS state. */
- u8 boost; /* Subject to priority boost. */
+ u8 boost ____cacheline_internodealigned_in_smp;
+ /* Subject to priority boost. */
unsigned long gpnum; /* Current gp number. */
unsigned long completed; /* # of last completed gp. */
struct task_struct *gp_kthread; /* Task for grace periods. */
atomic_long_t expedited_normal; /* # fallbacks to normal. */
atomic_t expedited_need_qs; /* # CPUs left to check in. */
wait_queue_head_t expedited_wq; /* Wait for check-ins. */
+ int ncpus_snap; /* # CPUs seen last time. */
unsigned long jiffies_force_qs; /* Time at which to invoke */
/* force_quiescent_state(). */
#define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */
#define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */
-/* Values for rcu_state structure's gp_flags field. */
-#define RCU_GP_WAIT_INIT 0 /* Initial state. */
+/* Values for rcu_state structure's gp_state field. */
+#define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */
#define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */
#define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */
#define RCU_GP_WAIT_FQS 3 /* Wait for force-quiescent-state time. */
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_print_detail_task_stall(struct rcu_state *rsp);
static int rcu_print_task_stall(struct rcu_node *rnp);
+ static int rcu_print_task_exp_stall(struct rcu_node *rnp);
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
static void rcu_preempt_check_callbacks(void);
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+void call_rcu(struct rcu_head *head, rcu_callback_t func);
static void __init __rcu_init_preempt(void);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
- static int rcu_preempted_readers_exp(struct rcu_node *rnp);
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
bool wake);
rcu_bootup_announce_oddness();
}
+ /* Flags for rcu_preempt_ctxt_queue() decision table. */
+ #define RCU_GP_TASKS 0x8
+ #define RCU_EXP_TASKS 0x4
+ #define RCU_GP_BLKD 0x2
+ #define RCU_EXP_BLKD 0x1
+
+ /*
+ * Queues a task preempted within an RCU-preempt read-side critical
+ * section into the appropriate location within the ->blkd_tasks list,
+ * depending on the states of any ongoing normal and expedited grace
+ * periods. The ->gp_tasks pointer indicates which element the normal
+ * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
+ * indicates which element the expedited grace period is waiting on (again,
+ * NULL if none). If a grace period is waiting on a given element in the
+ * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
+ * adding a task to the tail of the list blocks any grace period that is
+ * already waiting on one of the elements. In contrast, adding a task
+ * to the head of the list won't block any grace period that is already
+ * waiting on one of the elements.
+ *
+ * This queuing is imprecise, and can sometimes make an ongoing grace
+ * period wait for a task that is not strictly speaking blocking it.
+ * Given the choice, we needlessly block a normal grace period rather than
+ * blocking an expedited grace period.
+ *
+ * Note that an endless sequence of expedited grace periods still cannot
+ * indefinitely postpone a normal grace period. Eventually, all of the
+ * fixed number of preempted tasks blocking the normal grace period that are
+ * not also blocking the expedited grace period will resume and complete
+ * their RCU read-side critical sections. At that point, the ->gp_tasks
+ * pointer will equal the ->exp_tasks pointer, at which point the end of
+ * the corresponding expedited grace period will also be the end of the
+ * normal grace period.
+ */
+ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp,
+ unsigned long flags) __releases(rnp->lock)
+ {
+ int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
+ (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
+ (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
+ (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
+ struct task_struct *t = current;
+
+ /*
+ * Decide where to queue the newly blocked task. In theory,
+ * this could be an if-statement. In practice, when I tried
+ * that, it was quite messy.
+ */
+ switch (blkd_state) {
+ case 0:
+ case RCU_EXP_TASKS:
+ case RCU_EXP_TASKS + RCU_GP_BLKD:
+ case RCU_GP_TASKS:
+ case RCU_GP_TASKS + RCU_EXP_TASKS:
+
+ /*
+ * Blocking neither GP, or first task blocking the normal
+ * GP but not blocking the already-waiting expedited GP.
+ * Queue at the head of the list to avoid unnecessarily
+ * blocking the already-waiting GPs.
+ */
+ list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
+ break;
+
+ case RCU_EXP_BLKD:
+ case RCU_GP_BLKD:
+ case RCU_GP_BLKD + RCU_EXP_BLKD:
+ case RCU_GP_TASKS + RCU_EXP_BLKD:
+ case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
+ case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
+
+ /*
+ * First task arriving that blocks either GP, or first task
+ * arriving that blocks the expedited GP (with the normal
+ * GP already waiting), or a task arriving that blocks
+ * both GPs with both GPs already waiting. Queue at the
+ * tail of the list to avoid any GP waiting on any of the
+ * already queued tasks that are not blocking it.
+ */
+ list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
+ break;
+
+ case RCU_EXP_TASKS + RCU_EXP_BLKD:
+ case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
+ case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
+
+ /*
+ * Second or subsequent task blocking the expedited GP.
+ * The task either does not block the normal GP, or is the
+ * first task blocking the normal GP. Queue just after
+ * the first task blocking the expedited GP.
+ */
+ list_add(&t->rcu_node_entry, rnp->exp_tasks);
+ break;
+
+ case RCU_GP_TASKS + RCU_GP_BLKD:
+ case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
+
+ /*
+ * Second or subsequent task blocking the normal GP.
+ * The task does not block the expedited GP. Queue just
+ * after the first task blocking the normal GP.
+ */
+ list_add(&t->rcu_node_entry, rnp->gp_tasks);
+ break;
+
+ default:
+
+ /* Yet another exercise in excessive paranoia. */
+ WARN_ON_ONCE(1);
+ break;
+ }
+
+ /*
+ * We have now queued the task. If it was the first one to
+ * block either grace period, update the ->gp_tasks and/or
+ * ->exp_tasks pointers, respectively, to reference the newly
+ * blocked tasks.
+ */
+ if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
+ rnp->gp_tasks = &t->rcu_node_entry;
+ if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
+ rnp->exp_tasks = &t->rcu_node_entry;
+ raw_spin_unlock(&rnp->lock);
+
+ /*
+ * Report the quiescent state for the expedited GP. This expedited
+ * GP should not be able to end until we report, so there should be
+ * no need to check for a subsequent expedited GP. (Though we are
+ * still in a quiescent state in any case.)
+ */
+ if (blkd_state & RCU_EXP_BLKD &&
+ t->rcu_read_unlock_special.b.exp_need_qs) {
+ t->rcu_read_unlock_special.b.exp_need_qs = false;
+ rcu_report_exp_rdp(rdp->rsp, rdp, true);
+ } else {
+ WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
+ }
+ local_irq_restore(flags);
+ }
+
/*
* Record a preemptible-RCU quiescent state for the specified CPU. Note
* that this just means that the task currently running on the CPU is
*/
static void rcu_preempt_qs(void)
{
- if (!__this_cpu_read(rcu_data_p->passed_quiesce)) {
+ if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_preempt"),
__this_cpu_read(rcu_data_p->gpnum),
TPS("cpuqs"));
- __this_cpu_write(rcu_data_p->passed_quiesce, 1);
+ __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
current->rcu_read_unlock_special.b.need_qs = false;
}
t->rcu_blocked_node = rnp;
/*
- * If this CPU has already checked in, then this task
- * will hold up the next grace period rather than the
- * current grace period. Queue the task accordingly.
- * If the task is queued for the current grace period
- * (i.e., this CPU has not yet passed through a quiescent
- * state for the current grace period), then as long
- * as that task remains queued, the current grace period
- * cannot end. Note that there is some uncertainty as
- * to exactly when the current grace period started.
- * We take a conservative approach, which can result
- * in unnecessarily waiting on tasks that started very
- * slightly after the current grace period began. C'est
- * la vie!!!
- *
- * But first, note that the current CPU must still be
- * on line!
+ * Verify the CPU's sanity, trace the preemption, and
+ * then queue the task as required based on the states
+ * of any ongoing and expedited grace periods.
*/
WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
- if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
- list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
- rnp->gp_tasks = &t->rcu_node_entry;
- if (IS_ENABLED(CONFIG_RCU_BOOST) &&
- rnp->boost_tasks != NULL)
- rnp->boost_tasks = rnp->gp_tasks;
- } else {
- list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
- if (rnp->qsmask & rdp->grpmask)
- rnp->gp_tasks = &t->rcu_node_entry;
- }
trace_rcu_preempt_task(rdp->rsp->name,
t->pid,
(rnp->qsmask & rdp->grpmask)
? rnp->gpnum
: rnp->gpnum + 1);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ rcu_preempt_ctxt_queue(rnp, rdp, flags);
} else if (t->rcu_read_lock_nesting < 0 &&
t->rcu_read_unlock_special.s) {
unsigned long flags;
struct list_head *np;
bool drop_boost_mutex = false;
+ struct rcu_data *rdp;
struct rcu_node *rnp;
union rcu_special special;
local_irq_save(flags);
/*
- * If RCU core is waiting for this CPU to exit critical section,
- * let it know that we have done so. Because irqs are disabled,
+ * If RCU core is waiting for this CPU to exit its critical section,
+ * report the fact that it has exited. Because irqs are disabled,
* t->rcu_read_unlock_special cannot change.
*/
special = t->rcu_read_unlock_special;
}
}
+ /*
+ * Respond to a request for an expedited grace period, but only if
+ * we were not preempted, meaning that we were running on the same
+ * CPU throughout. If we were preempted, the exp_need_qs flag
+ * would have been cleared at the time of the first preemption,
+ * and the quiescent state would be reported when we were dequeued.
+ */
+ if (special.b.exp_need_qs) {
+ WARN_ON_ONCE(special.b.blocked);
+ t->rcu_read_unlock_special.b.exp_need_qs = false;
+ rdp = this_cpu_ptr(rcu_state_p->rda);
+ rcu_report_exp_rdp(rcu_state_p, rdp, true);
+ if (!t->rcu_read_unlock_special.s) {
+ local_irq_restore(flags);
+ return;
+ }
+ }
+
/* Hardware IRQ handlers cannot block, complain if they get here. */
if (in_irq() || in_serving_softirq()) {
lockdep_rcu_suspicious(__FILE__, __LINE__,
"rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
- pr_alert("->rcu_read_unlock_special: %#x (b: %d, nq: %d)\n",
+ pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
t->rcu_read_unlock_special.s,
t->rcu_read_unlock_special.b.blocked,
+ t->rcu_read_unlock_special.b.exp_need_qs,
t->rcu_read_unlock_special.b.need_qs);
local_irq_restore(flags);
return;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
- empty_exp = !rcu_preempted_readers_exp(rnp);
+ empty_exp = sync_rcu_preempt_exp_done(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
np = rcu_next_node_entry(t, rnp);
list_del_init(&t->rcu_node_entry);
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
* so we must take a snapshot of the expedited state.
*/
- empty_exp_now = !rcu_preempted_readers_exp(rnp);
+ empty_exp_now = sync_rcu_preempt_exp_done(rnp);
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
rnp->gpnum,
return ndetected;
}
+ /*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each that is blocking the current
+ * expedited grace period.
+ */
+ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+ {
+ struct task_struct *t;
+ int ndetected = 0;
+
+ if (!rnp->exp_tasks)
+ return 0;
+ t = list_entry(rnp->exp_tasks->prev,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ pr_cont(" P%d", t->pid);
+ ndetected++;
+ }
+ return ndetected;
+ }
+
/*
* Check that the list of blocked tasks for the newly completed grace
* period is in fact empty. It is a serious bug to complete a grace
return;
}
if (t->rcu_read_lock_nesting > 0 &&
- __this_cpu_read(rcu_data_p->qs_pending) &&
- !__this_cpu_read(rcu_data_p->passed_quiesce))
+ __this_cpu_read(rcu_data_p->core_needs_qs) &&
+ __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))
t->rcu_read_unlock_special.b.need_qs = true;
}
/*
* Queue a preemptible-RCU callback for invocation after a grace period.
*/
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, rcu_state_p, -1, 0);
}
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
- static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
-
/*
- * Return non-zero if there are any tasks in RCU read-side critical
- * sections blocking the current preemptible-RCU expedited grace period.
- * If there is no preemptible-RCU expedited grace period currently in
- * progress, returns zero unconditionally.
+ * Remote handler for smp_call_function_single(). If there is an
+ * RCU read-side critical section in effect, request that the
+ * next rcu_read_unlock() record the quiescent state up the
+ * ->expmask fields in the rcu_node tree. Otherwise, immediately
+ * report the quiescent state.
*/
- static int rcu_preempted_readers_exp(struct rcu_node *rnp)
+ static void sync_rcu_exp_handler(void *info)
{
- return rnp->exp_tasks != NULL;
- }
-
- /*
- * return non-zero if there is no RCU expedited grace period in progress
- * for the specified rcu_node structure, in other words, if all CPUs and
- * tasks covered by the specified rcu_node structure have done their bit
- * for the current expedited grace period. Works only for preemptible
- * RCU -- other RCU implementation use other means.
- *
- * Caller must hold the root rcu_node's exp_funnel_mutex.
- */
- static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
- {
- return !rcu_preempted_readers_exp(rnp) &&
- READ_ONCE(rnp->expmask) == 0;
- }
-
- /*
- * Report the exit from RCU read-side critical section for the last task
- * that queued itself during or before the current expedited preemptible-RCU
- * grace period. This event is reported either to the rcu_node structure on
- * which the task was queued or to one of that rcu_node structure's ancestors,
- * recursively up the tree. (Calm down, calm down, we do the recursion
- * iteratively!)
- *
- * Caller must hold the root rcu_node's exp_funnel_mutex.
- */
- static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
- bool wake)
- {
- unsigned long flags;
- unsigned long mask;
-
- raw_spin_lock_irqsave(&rnp->lock, flags);
- smp_mb__after_unlock_lock();
- for (;;) {
- if (!sync_rcu_preempt_exp_done(rnp)) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- break;
- }
- if (rnp->parent == NULL) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- if (wake) {
- smp_mb(); /* EGP done before wake_up(). */
- wake_up(&sync_rcu_preempt_exp_wq);
- }
- break;
- }
- mask = rnp->grpmask;
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
- rnp = rnp->parent;
- raw_spin_lock(&rnp->lock); /* irqs already disabled */
- smp_mb__after_unlock_lock();
- rnp->expmask &= ~mask;
- }
- }
-
- /*
- * Snapshot the tasks blocking the newly started preemptible-RCU expedited
- * grace period for the specified rcu_node structure, phase 1. If there
- * are such tasks, set the ->expmask bits up the rcu_node tree and also
- * set the ->expmask bits on the leaf rcu_node structures to tell phase 2
- * that work is needed here.
- *
- * Caller must hold the root rcu_node's exp_funnel_mutex.
- */
- static void
- sync_rcu_preempt_exp_init1(struct rcu_state *rsp, struct rcu_node *rnp)
- {
- unsigned long flags;
- unsigned long mask;
- struct rcu_node *rnp_up;
-
- raw_spin_lock_irqsave(&rnp->lock, flags);
- smp_mb__after_unlock_lock();
- WARN_ON_ONCE(rnp->expmask);
- WARN_ON_ONCE(rnp->exp_tasks);
- if (!rcu_preempt_has_tasks(rnp)) {
- /* No blocked tasks, nothing to do. */
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- return;
- }
- /* Call for Phase 2 and propagate ->expmask bits up the tree. */
- rnp->expmask = 1;
- rnp_up = rnp;
- while (rnp_up->parent) {
- mask = rnp_up->grpmask;
- rnp_up = rnp_up->parent;
- if (rnp_up->expmask & mask)
- break;
- raw_spin_lock(&rnp_up->lock); /* irqs already off */
- smp_mb__after_unlock_lock();
- rnp_up->expmask |= mask;
- raw_spin_unlock(&rnp_up->lock); /* irqs still off */
- }
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- }
-
- /*
- * Snapshot the tasks blocking the newly started preemptible-RCU expedited
- * grace period for the specified rcu_node structure, phase 2. If the
- * leaf rcu_node structure has its ->expmask field set, check for tasks.
- * If there are some, clear ->expmask and set ->exp_tasks accordingly,
- * then initiate RCU priority boosting. Otherwise, clear ->expmask and
- * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits,
- * enabling rcu_read_unlock_special() to do the bit-clearing.
- *
- * Caller must hold the root rcu_node's exp_funnel_mutex.
- */
- static void
- sync_rcu_preempt_exp_init2(struct rcu_state *rsp, struct rcu_node *rnp)
- {
- unsigned long flags;
-
- raw_spin_lock_irqsave(&rnp->lock, flags);
- smp_mb__after_unlock_lock();
- if (!rnp->expmask) {
- /* Phase 1 didn't do anything, so Phase 2 doesn't either. */
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- return;
- }
-
- /* Phase 1 is over. */
- rnp->expmask = 0;
+ struct rcu_data *rdp;
+ struct rcu_state *rsp = info;
+ struct task_struct *t = current;
/*
- * If there are still blocked tasks, set up ->exp_tasks so that
- * rcu_read_unlock_special() will wake us and then boost them.
+ * Within an RCU read-side critical section, request that the next
+ * rcu_read_unlock() report. Unless this RCU read-side critical
+ * section has already blocked, in which case it is already set
+ * up for the expedited grace period to wait on it.
*/
- if (rcu_preempt_has_tasks(rnp)) {
- rnp->exp_tasks = rnp->blkd_tasks.next;
- rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
+ if (t->rcu_read_lock_nesting > 0 &&
+ !t->rcu_read_unlock_special.b.blocked) {
+ t->rcu_read_unlock_special.b.exp_need_qs = true;
return;
}
- /* No longer any blocked tasks, so undo bit setting. */
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- rcu_report_exp_rnp(rsp, rnp, false);
+ /*
+ * We are either exiting an RCU read-side critical section (negative
+ * values of t->rcu_read_lock_nesting) or are not in one at all
+ * (zero value of t->rcu_read_lock_nesting). Or we are in an RCU
+ * read-side critical section that blocked before this expedited
+ * grace period started. Either way, we can immediately report
+ * the quiescent state.
+ */
+ rdp = this_cpu_ptr(rsp->rda);
+ rcu_report_exp_rdp(rsp, rdp, true);
}
/**
rcu_exp_gp_seq_start(rsp);
- /* force all RCU readers onto ->blkd_tasks lists. */
- synchronize_sched_expedited();
-
- /*
- * Snapshot current state of ->blkd_tasks lists into ->expmask.
- * Phase 1 sets bits and phase 2 permits rcu_read_unlock_special()
- * to start clearing them. Doing this in one phase leads to
- * strange races between setting and clearing bits, so just say "no"!
- */
- rcu_for_each_leaf_node(rsp, rnp)
- sync_rcu_preempt_exp_init1(rsp, rnp);
- rcu_for_each_leaf_node(rsp, rnp)
- sync_rcu_preempt_exp_init2(rsp, rnp);
+ /* Initialize the rcu_node tree in preparation for the wait. */
+ sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler);
/* Wait for snapshotted ->blkd_tasks lists to drain. */
rnp = rcu_get_root(rsp);
- wait_event(sync_rcu_preempt_exp_wq,
- sync_rcu_preempt_exp_done(rnp));
+ synchronize_sched_expedited_wait(rsp);
/* Clean up and exit. */
rcu_exp_gp_seq_end(rsp);
return 0;
}
+ /*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections that are
+ * blocking the current expedited grace period.
+ */
+ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+ {
+ return 0;
+ }
+
/*
* Because there is no preemptible RCU, there can be no readers blocked,
* so there is no need to check for blocked tasks. So check only for
ticks_value = rsp->gpnum - rdp->gpnum;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
- pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
- cpu, ticks_value, ticks_title,
+ pr_err("\t%d-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
+ cpu,
+ "O."[!!cpu_online(cpu)],
+ "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
+ "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
+ ticks_value, ticks_title,
atomic_read(&rdtp->dynticks) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
if (!rdp->beenonline)
return;
- seq_printf(m, "%3d%cc=%ld g=%ld pq=%d/%d qp=%d",
+ seq_printf(m, "%3d%cc=%ld g=%ld cnq=%d/%d:%d",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? '!' : ' ',
ulong2long(rdp->completed), ulong2long(rdp->gpnum),
- rdp->passed_quiesce,
+ rdp->cpu_no_qs.b.norm,
rdp->rcu_qs_ctr_snap == per_cpu(rcu_qs_ctr, rdp->cpu),
- rdp->qs_pending);
+ rdp->core_needs_qs);
seq_printf(m, " dt=%d/%llx/%d df=%lu",
atomic_read(&rdp->dynticks->dynticks),
rdp->dynticks->dynticks_nesting,
gpnum = rsp->gpnum;
seq_printf(m, "c=%ld g=%ld s=%d jfq=%ld j=%x ",
ulong2long(rsp->completed), ulong2long(gpnum),
- rsp->fqs_state,
+ rsp->gp_state,
(long)(rsp->jiffies_force_qs - jiffies),
(int)(jiffies & 0xffff));
seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
cpu_is_offline(rdp->cpu) ? '!' : ' ',
rdp->n_rcu_pending);
seq_printf(m, "qsp=%ld rpq=%ld cbr=%ld cng=%ld ",
- rdp->n_rp_qs_pending,
+ rdp->n_rp_core_needs_qs,
rdp->n_rp_report_qs,
rdp->n_rp_cb_ready,
rdp->n_rp_cpu_needs_gp);
projects / linux.git / commitdiff