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perf/core: Fix endless multiplex timer

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commit 90c91dfb86d0ff545bd329d3ddd72c147e2ae198 upstream.

Kan and Andi reported that we fail to kill rotation when the flexible
events go empty, but the context does not. XXX moar

Fixes: fd7d55172d ("perf/cgroups: Don't rotate events for cgroups unnecessarily")
Reported-by: Andi Kleen <[email protected]>
Reported-by: Kan Liang <[email protected]>
Tested-by: Kan Liang <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Cc: Robin Murphy <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Peter Zijlstra 2020-03-05 13:38:51 +01:00 • committed by Greg Kroah-Hartman
commit 68a2350376
1 changed files with 14 additions and 6 deletions
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20
kernel/events/core.c
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@ -2171,6 +2171,7 @@ __perf_remove_from_context(struct perf_event *event,
if (!ctx->nr_events && ctx->is_active) {
ctx->is_active = 0;
ctx->rotate_necessary = 0;
if (ctx->task) {
WARN_ON_ONCE(cpuctx->task_ctx != ctx);
cpuctx->task_ctx = NULL;
@ -3047,12 +3048,6 @@ static void ctx_sched_out(struct perf_event_context *ctx,
if (!ctx->nr_active || !(is_active & EVENT_ALL))
return;
/*
* If we had been multiplexing, no rotations are necessary, now no events
* are active.
*/
ctx->rotate_necessary = 0;
perf_pmu_disable(ctx->pmu);
if (is_active & EVENT_PINNED) {
list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list)
@ -3062,6 +3057,13 @@ static void ctx_sched_out(struct perf_event_context *ctx,
if (is_active & EVENT_FLEXIBLE) {
list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list)
group_sched_out(event, cpuctx, ctx);
/*
* Since we cleared EVENT_FLEXIBLE, also clear
* rotate_necessary, is will be reset by
* ctx_flexible_sched_in() when needed.
*/
ctx->rotate_necessary = 0;
}
perf_pmu_enable(ctx->pmu);
}
@ -3800,6 +3802,12 @@ ctx_event_to_rotate(struct perf_event_context *ctx)
typeof(*event), group_node);
}
/*
* Unconditionally clear rotate_necessary; if ctx_flexible_sched_in()
* finds there are unschedulable events, it will set it again.
*/
ctx->rotate_necessary = 0;
return event;
}