From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Sebastian Siewior <bigeasy@linutronix.de>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [patch V3 23/32] perf/tracing/cpuhotplug: Fix locking order
Date: Tue, 30 May 2017 13:22:35 +0200 [thread overview]
Message-ID: <20170530112235.e3rt7rmfubamn3nq@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170524183018.GH3956@linux.vnet.ibm.com>
On Wed, May 24, 2017 at 11:30:18AM -0700, Paul E. McKenney wrote:
> > @@ -8920,7 +8912,7 @@ perf_event_mux_interval_ms_store(struct
> > pmu->hrtimer_interval_ms = timer;
> >
> > /* update all cpuctx for this PMU */
> > - get_online_cpus();
> > + cpus_read_lock();
>
> OK, I'll bite...
>
> Why is this piece using cpus_read_lock() instead of pmus_lock?
>
> My guess is for the benefit of the cpu_function_call() below, but if
> the code instead cycled through the perf_online_mask, wouldn't any
> CPU selected be guaranteed to be online?
>
> Or is there some reason that it would be necessary to specially handle
> CPUs that perf does not consider to be active, but that are still at
> least partway online?
Mostly just lazy. This code path didn't present a problem with the lock
ordering. Find the conversion below.
>
> > for_each_online_cpu(cpu) {
> > struct perf_cpu_context *cpuctx;
> > cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
> > @@ -8929,7 +8921,7 @@ perf_event_mux_interval_ms_store(struct
> > cpu_function_call(cpu,
> > (remote_function_f)perf_mux_hrtimer_restart, cpuctx);
> > }
> > - put_online_cpus();
> > + cpus_read_unlock();
> > mutex_unlock(&mux_interval_mutex);
> >
> > return count;
---
Subject: perf: Complete CPU hotplug conversion
Remove the last cpuc_read_lock() user in perf in favour of our internal
state. This conversion is non critical as the lock ordering wasn't
problematic but its nice to be consistent.
Reported-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/events/core.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 8d6acaeeea17..ad4f7f03b519 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -389,6 +389,16 @@ static atomic_t nr_switch_events __read_mostly;
static LIST_HEAD(pmus);
static DEFINE_MUTEX(pmus_lock);
static struct srcu_struct pmus_srcu;
+
+/*
+ * CPU hotplug handling, also see perf_event_{exit,init}_cpu().
+ *
+ * We use @pmus_lock to serialize PMU (un)registration against CPU hotplug,
+ * tracking the online state in @perf_online_mask and
+ * pmu->pmu_cpu_context->online. That latter is set while holding ctx->mutex
+ * and therefore holding ctx->mutex is sufficient to serialize against
+ * hotplug wrt cpuctx->online.
+ */
static cpumask_var_t perf_online_mask;
/*
@@ -8887,8 +8897,6 @@ perf_event_mux_interval_ms_show(struct device *dev,
return snprintf(page, PAGE_SIZE-1, "%d\n", pmu->hrtimer_interval_ms);
}
-static DEFINE_MUTEX(mux_interval_mutex);
-
static ssize_t
perf_event_mux_interval_ms_store(struct device *dev,
struct device_attribute *attr,
@@ -8908,12 +8916,12 @@ perf_event_mux_interval_ms_store(struct device *dev,
if (timer == pmu->hrtimer_interval_ms)
return count;
- mutex_lock(&mux_interval_mutex);
+ /* use pmus_lock to order against hotplug and self serialize */
+ mutex_lock(&pmus_lock);
pmu->hrtimer_interval_ms = timer;
/* update all cpuctx for this PMU */
- cpus_read_lock();
- for_each_online_cpu(cpu) {
+ for_each_cpu(cpu, perf_online_mask) {
struct perf_cpu_context *cpuctx;
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * timer);
@@ -8921,8 +8929,7 @@ perf_event_mux_interval_ms_store(struct device *dev,
cpu_function_call(cpu,
(remote_function_f)perf_mux_hrtimer_restart, cpuctx);
}
- cpus_read_unlock();
- mutex_unlock(&mux_interval_mutex);
+ mutex_unlock(&pmus_lock);
return count;
}
next prev parent reply other threads:[~2017-05-30 11:22 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-24 8:15 [patch V3 00/32] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Thomas Gleixner
2017-05-24 8:15 ` [patch V3 01/32] cpu/hotplug: Provide cpus_read|write_[un]lock() Thomas Gleixner
2017-05-24 16:25 ` Paul E. McKenney
2017-05-26 8:31 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 02/32] cpu/hotplug: Provide lockdep_assert_cpus_held() Thomas Gleixner
2017-05-24 16:26 ` Paul E. McKenney
2017-05-26 8:32 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 03/32] cpu/hotplug: Provide cpuhp_setup/remove_state[_nocalls]_cpuslocked() Thomas Gleixner
2017-05-26 8:32 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 04/32] cpu/hotplug: Add __cpuhp_state_add_instance_cpuslocked() Thomas Gleixner
2017-05-26 8:33 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 05/32] stop_machine: Provide stop_machine_cpuslocked() Thomas Gleixner
2017-05-24 17:42 ` Paul E. McKenney
2017-05-26 8:33 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 06/32] padata: Make padata_alloc() static Thomas Gleixner
2017-05-26 8:34 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 07/32] padata: Avoid nested calls to cpus_read_lock() in pcrypt_init_padata() Thomas Gleixner
2017-05-26 8:35 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 08/32] x86/mtrr: Remove get_online_cpus() from mtrr_save_state() Thomas Gleixner
2017-05-26 8:35 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 09/32] cpufreq: Use cpuhp_setup_state_nocalls_cpuslocked() Thomas Gleixner
2017-05-26 8:36 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 10/32] KVM/PPC/Book3S HV: " Thomas Gleixner
2017-05-26 8:36 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 11/32] hwtracing/coresight-etm3x: " Thomas Gleixner
2017-05-25 16:46 ` Mathieu Poirier
2017-05-26 8:37 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 12/32] hwtracing/coresight-etm4x: " Thomas Gleixner
2017-05-25 16:47 ` Mathieu Poirier
2017-05-26 8:37 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 13/32] perf/x86/intel/cqm: Use cpuhp_setup_state_cpuslocked() Thomas Gleixner
2017-05-26 8:38 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 14/32] ARM/hw_breakpoint: " Thomas Gleixner
2017-05-26 8:38 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 15/32] s390/kernel: Use stop_machine_cpuslocked() Thomas Gleixner
2017-05-24 10:57 ` Heiko Carstens
2017-05-26 8:39 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 16/32] powerpc/powernv: " Thomas Gleixner
2017-05-26 8:40 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 17/32] cpu/hotplug: Use stop_machine_cpuslocked() in takedown_cpu() Thomas Gleixner
2017-05-26 8:40 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 18/32] x86/perf: Drop EXPORT of perf_check_microcode Thomas Gleixner
2017-05-26 8:41 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 19/32] perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode() Thomas Gleixner
2017-05-26 8:41 ` [tip:smp/hotplug] " tip-bot for Sebastian Andrzej Siewior
2017-05-24 8:15 ` [patch V3 20/32] PCI: Use cpu_hotplug_disable() instead of get_online_cpus() Thomas Gleixner
2017-05-26 8:42 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 21/32] PCI: Replace the racy recursion prevention Thomas Gleixner
2017-05-26 8:42 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 22/32] ACPI/processor: Use cpu_hotplug_disable() instead of get_online_cpus() Thomas Gleixner
2017-05-26 8:43 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 23/32] perf/tracing/cpuhotplug: Fix locking order Thomas Gleixner
2017-05-24 18:30 ` Paul E. McKenney
2017-05-24 18:47 ` Thomas Gleixner
2017-05-24 21:10 ` Paul E. McKenney
2017-05-30 11:22 ` Peter Zijlstra [this message]
2017-05-30 16:25 ` Paul E. McKenney
2017-05-26 8:43 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 24/32] jump_label: Reorder hotplug lock and jump_label_lock Thomas Gleixner
2017-05-24 12:50 ` David Miller
2017-05-26 8:44 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 25/32] kprobes: Cure hotplug lock ordering issues Thomas Gleixner
2017-05-24 15:54 ` Masami Hiramatsu
2017-05-26 7:47 ` Thomas Gleixner
2017-05-26 8:45 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 26/32] arm64: Prevent cpu hotplug rwsem recursion Thomas Gleixner
2017-05-26 8:45 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 27/32] arm: Prevent " Thomas Gleixner
2017-05-26 8:46 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 28/32] s390: " Thomas Gleixner
2017-05-24 10:57 ` Heiko Carstens
2017-05-26 8:46 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 29/32] cpu/hotplug: Convert hotplug locking to percpu rwsem Thomas Gleixner
2017-05-26 8:47 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 30/32] sched: Provide is_percpu_thread() helper Thomas Gleixner
2017-05-26 8:47 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 31/32] acpi/processor: Prevent cpu hotplug deadlock Thomas Gleixner
2017-05-26 8:48 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 8:15 ` [patch V3 32/32] cpuhotplug: Link lock stacks for hotplug callbacks Thomas Gleixner
2017-05-26 8:48 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2017-05-24 16:22 ` [patch V3 00/32] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Paul E. McKenney
2017-05-26 7:03 ` Ingo Molnar
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