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Code Issues Releases Wiki Activity

perf/core: Fix cgroup events tracking

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We encounter perf warnings when using cgroup events like:

  cd /sys/fs/cgroup
  mkdir test
  perf stat -e cycles -a -G test

Which then triggers:

  WARNING: CPU: 0 PID: 690 at kernel/events/core.c:849 perf_cgroup_switch+0xb2/0xc0
  Call Trace:
   <TASK>
   __schedule+0x4ae/0x9f0
   ? _raw_spin_unlock_irqrestore+0x23/0x40
   ? __cond_resched+0x18/0x20
   preempt_schedule_common+0x2d/0x70
   __cond_resched+0x18/0x20
   wait_for_completion+0x2f/0x160
   ? cpu_stop_queue_work+0x9e/0x130
   affine_move_task+0x18a/0x4f0

  WARNING: CPU: 0 PID: 690 at kernel/events/core.c:829 ctx_sched_in+0x1cf/0x1e0
  Call Trace:
   <TASK>
   ? ctx_sched_out+0xb7/0x1b0
   perf_cgroup_switch+0x88/0xc0
   __schedule+0x4ae/0x9f0
   ? _raw_spin_unlock_irqrestore+0x23/0x40
   ? __cond_resched+0x18/0x20
   preempt_schedule_common+0x2d/0x70
   __cond_resched+0x18/0x20
   wait_for_completion+0x2f/0x160
   ? cpu_stop_queue_work+0x9e/0x130
   affine_move_task+0x18a/0x4f0

The above two warnings are not complete here since I remove other
unimportant information. The problem is caused by the perf cgroup
events tracking:

  CPU0					CPU1
  perf_event_open()
    perf_event_alloc()
      account_event()
	account_event_cpu()
	  atomic_inc(perf_cgroup_events)
					  __perf_event_task_sched_out()
					    if (atomic_read(perf_cgroup_events))
					      perf_cgroup_switch()
						// kernel/events/core.c:849
						WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0)
						if (READ_ONCE(cpuctx->cgrp) == cgrp) // false
						  return
						perf_ctx_lock()
						ctx_sched_out()
						cpuctx->cgrp = cgrp
						ctx_sched_in()
						  perf_cgroup_set_timestamp()
						    // kernel/events/core.c:829
						    WARN_ON_ONCE(!ctx->nr_cgroups)
						perf_ctx_unlock()
    perf_install_in_context()
      cpu_function_call()
					  __perf_install_in_context()
					    add_event_to_ctx()
					      list_add_event()
						perf_cgroup_event_enable()
						  ctx->nr_cgroups++
						  cpuctx->cgrp = X

We can see from above that we wrongly use percpu atomic perf_cgroup_events
to check if we need to perf_cgroup_switch(), which should only be used
when we know this CPU has cgroup events enabled.

The commit bd27568117 ("perf: Rewrite core context handling") change
to have only one context per-CPU, so we can just use cpuctx->cgrp to
check if this CPU has cgroup events enabled.

So percpu atomic perf_cgroup_events is not needed.

Fixes: bd27568117 ("perf: Rewrite core context handling")
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lkml.kernel.org/r/20221207124023.66252-1-zhouchengming@bytedance.com
This commit is contained in:
Chengming Zhou 2022-12-07 20:40:23 +08:00 committed by Peter Zijlstra
parent e2d3714846
commit f841b682ba
1 changed files with 10 additions and 32 deletions
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42
kernel/events/core.c
View file

@ -380,7 +380,6 @@ enum event_type_t {
/*
* perf_sched_events : >0 events exist
* perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu
*/
static void perf_sched_delayed(struct work_struct *work);
@ -389,7 +388,6 @@ static DECLARE_DELAYED_WORK(perf_sched_work, perf_sched_delayed);
static DEFINE_MUTEX(perf_sched_mutex);
static atomic_t perf_sched_count;
static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
static DEFINE_PER_CPU(struct pmu_event_list, pmu_sb_events);
static atomic_t nr_mmap_events __read_mostly;
@ -844,9 +842,16 @@ static void perf_cgroup_switch(struct task_struct *task)
struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
struct perf_cgroup *cgrp;
cgrp = perf_cgroup_from_task(task, NULL);
/*
* cpuctx->cgrp is set when the first cgroup event enabled,
* and is cleared when the last cgroup event disabled.
*/
if (READ_ONCE(cpuctx->cgrp) == NULL)
return;
WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0);
cgrp = perf_cgroup_from_task(task, NULL);
if (READ_ONCE(cpuctx->cgrp) == cgrp)
return;
@ -3631,8 +3636,7 @@ void __perf_event_task_sched_out(struct task_struct *task,
* to check if we have to switch out PMU state.
* cgroup event are system-wide mode only
*/
if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
perf_cgroup_switch(next);
perf_cgroup_switch(next);
}
static bool perf_less_group_idx(const void *l, const void *r)
@ -4974,15 +4978,6 @@ static void unaccount_pmu_sb_event(struct perf_event *event)
detach_sb_event(event);
}
static void unaccount_event_cpu(struct perf_event *event, int cpu)
{
if (event->parent)
return;
if (is_cgroup_event(event))
atomic_dec(&per_cpu(perf_cgroup_events, cpu));
}
#ifdef CONFIG_NO_HZ_FULL
static DEFINE_SPINLOCK(nr_freq_lock);
#endif
@ -5048,8 +5043,6 @@ static void unaccount_event(struct perf_event *event)
schedule_delayed_work(&perf_sched_work, HZ);
}
unaccount_event_cpu(event, event->cpu);
unaccount_pmu_sb_event(event);
}
@ -11679,15 +11672,6 @@ static void account_pmu_sb_event(struct perf_event *event)
attach_sb_event(event);
}
static void account_event_cpu(struct perf_event *event, int cpu)
{
if (event->parent)
return;
if (is_cgroup_event(event))
atomic_inc(&per_cpu(perf_cgroup_events, cpu));
}
/* Freq events need the tick to stay alive (see perf_event_task_tick). */
static void account_freq_event_nohz(void)
{
@ -11775,8 +11759,6 @@ static void account_event(struct perf_event *event)
}
enabled:
account_event_cpu(event, event->cpu);
account_pmu_sb_event(event);
}
@ -12822,13 +12804,11 @@ static void __perf_pmu_remove(struct perf_event_context *ctx,
perf_event_groups_for_cpu_pmu(event, groups, cpu, pmu) {
perf_remove_from_context(event, 0);
unaccount_event_cpu(event, cpu);
put_pmu_ctx(event->pmu_ctx);
list_add(&event->migrate_entry, events);
for_each_sibling_event(sibling, event) {
perf_remove_from_context(sibling, 0);
unaccount_event_cpu(sibling, cpu);
put_pmu_ctx(sibling->pmu_ctx);
list_add(&sibling->migrate_entry, events);
}
@ -12847,7 +12827,6 @@ static void __perf_pmu_install_event(struct pmu *pmu,
if (event->state >= PERF_EVENT_STATE_OFF)
event->state = PERF_EVENT_STATE_INACTIVE;
account_event_cpu(event, cpu);
perf_install_in_context(ctx, event, cpu);
}
@ -13742,8 +13721,7 @@ static int __perf_cgroup_move(void *info)
struct task_struct *task = info;
preempt_disable();
if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
perf_cgroup_switch(task);
perf_cgroup_switch(task);
preempt_enable();
return 0;