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Subject[tip:perf/urgent] perf: Do not set task_ctx pointer in cpuctx if there are no events in the context
Commit-ID:  1d5f003f5a964711853514b04ddc872eec0fdc7b
Gitweb: http://git.kernel.org/tip/1d5f003f5a964711853514b04ddc872eec0fdc7b
Author: Gleb Natapov <gleb@redhat.com>
AuthorDate: Sun, 23 Oct 2011 19:10:33 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 14 Nov 2011 13:01:21 +0100

perf: Do not set task_ctx pointer in cpuctx if there are no events in the context

Do not set task_ctx pointer during sched_in if there are 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.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111023171033.GI17571@redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/events/core.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e8457d..b0c1186 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2173,7 +2173,8 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,

perf_event_sched_in(cpuctx, ctx, task);

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

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

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