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perf/core: Remove WARN from perf_event_read()

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This effectively reverts commit:

  71e7bc2bab ("perf/core: Check return value of the perf_event_read() IPI")

... and puts in a comment explaining why we ignore the return value.

Reported-by: Vegard Nossum <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: David Carrillo-Cisneros <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 71e7bc2bab ("perf/core: Check return value of the perf_event_read() IPI")
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra authored and Ingo Molnar committed 2016-09-05 11:55:00 +02:00
1 parent c6935931c1
commit 5876314875
1 file changed
+12 -4
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kernel/events/core.c
+12 -4
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@@ -3549,10 +3549,18 @@ static int perf_event_read(struct perf_event *event, bool group)
.group = group,
.ret = 0,
};
ret = smp_call_function_single(event->oncpu, __perf_event_read, &data, 1);
/* The event must have been read from an online CPU: */
WARN_ON_ONCE(ret);
ret = ret ? : data.ret;
/*
* Purposely ignore the smp_call_function_single() return
* value.
*
* If event->oncpu isn't a valid CPU it means the event got
* scheduled out and that will have updated the event count.
*
* Therefore, either way, we'll have an up-to-date event count
* after this.
*/
(void)smp_call_function_single(event->oncpu, __perf_event_read, &data, 1);
ret = data.ret;
} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
struct perf_event_context *ctx = event->ctx;
unsigned long flags;