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SubjectRe: [PATCH] perf: do not set task_ctx pointer in cpuctx if there is no events in the context
On Mon, Nov 07, 2011 at 02:00:11PM +0100, Peter Zijlstra wrote:
> On Thu, 2011-11-03 at 09:41 +0200, Gleb Natapov wrote:
> > Ingo, Peter can you look into this please.
>
> queued it and the jump_label thing.
I see jump_label thing in tip/perf/core but not this one yet. This is
good because this one needs amendment :) See below.

---

Do not set task_ctx pointer during sched_in if there is no
events associated with the context. Otherwise if during task
execution total number of events in the system will become zero
perf_event_context_sched_out() will not be called and cpuctx->task_ctx
will be left with a stale value. Also perf_event_sched_in() shouldn't try
to schedule task events in this case otherwise cpuctx->task_ctx->is_active
will not be cleared during sched_out and will become incorrect.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d1a1bee..7210657 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2171,9 +2171,10 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
*/
cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);

- perf_event_sched_in(cpuctx, ctx, task);
+ if (ctx->nr_events)
+ cpuctx->task_ctx = ctx;

- cpuctx->task_ctx = ctx;
+ perf_event_sched_in(cpuctx, cpuctx->task_ctx, task);

perf_pmu_enable(ctx->pmu);
perf_ctx_unlock(cpuctx, ctx);
--
Gleb.

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