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Date: Tue, 6 Oct 2015 09:29:37 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 18/18] rcu: Better hotplug handling for synchronize_sched_expedited()
Earlier versions of synchronize_sched_expedited() can prematurely end
grace periods due to the fact that a CPU marked as cpu_is_offline()
can still be using RCU read-side critical sections during the time that
CPU makes its last pass through the scheduler and into the idle loop
and during the time that a given CPU is in the process of coming online.
This commit therefore eliminates this window by adding additional
interaction with the CPU-hotplug operations.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 62 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ed957c3b6c86..80c834c46b8d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -246,17 +246,23 @@ static int rcu_gp_in_progress(struct rcu_state *rsp)
*/
void rcu_sched_qs(void)
{
+ 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.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);
}
}
@@ -3553,7 +3559,10 @@ static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
raw_spin_lock_irqsave(&rnp->lock, flags);
smp_mb__after_unlock_lock();
- WARN_ON_ONCE((rnp->expmask & mask) != mask);
+ 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. */
}
@@ -3644,12 +3653,37 @@ static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
}
/* Invoked on each online non-idle CPU for expedited quiescent state. */
-static void synchronize_sched_expedited_cpu_stop(void *data)
+static void sync_sched_exp_handler(void *data)
{
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = data;
+
+ 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.
@@ -3677,7 +3711,6 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
if (raw_smp_processor_id() == cpu ||
- cpu_is_offline(cpu) ||
!(atomic_add_return(0, &rdtp->dynticks) & 0x1))
mask_ofl_test |= rdp->grpmask;
}
@@ -3697,9 +3730,28 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
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)
+ 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;
@@ -3796,7 +3848,7 @@ void synchronize_sched_expedited(void)
return; /* Someone else did our work for us. */
rcu_exp_gp_seq_start(rsp);
- sync_rcu_exp_select_cpus(rsp, synchronize_sched_expedited_cpu_stop);
+ sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
synchronize_sched_expedited_wait(rsp);
rcu_exp_gp_seq_end(rsp);
@@ -4183,6 +4235,7 @@ int rcu_cpu_notify(struct notifier_block *self,
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:
@@ -4195,7 +4248,10 @@ int rcu_cpu_notify(struct notifier_block *self,
break;
case CPU_DYING_IDLE:
/* QS for any half-done expedited RCU-sched GP. */
- rcu_sched_qs();
+ 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);
--
2.5.2
--
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