linux-kernel - [PATCH] perf, powerpc: Fix power_pmu_event

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Message-ID: <20101019055535.GA10398@drongo>
Date:	Tue, 19 Oct 2010 16:55:35 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Alexey Kardashevskiy <aik@....ibm.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: [PATCH] perf, powerpc: Fix power_pmu_event_init to not use
 event->ctx

Commit c3f00c70 ("perf: Separate find_get_context() from event
initialization") changed the generic perf_event code to call
perf_event_alloc, which calls the arch-specific event_init code,
before looking up the context for the new event.  Unfortunately,
power_pmu_event_init uses event->ctx->task to see whether the new
event is a per-task event or a system-wide event, and thus crashes
since event->ctx is NULL at the point where power_pmu_event_init gets
called.

(The reason it needs to know whether it is a per-task event is because
there are some hardware events on Power systems which only count when
the processor is not idle, and there are some fixed-function counters
which count such events.  For example, the "run cycles" event counts
cycles when the processor is not idle.  If the user asks to count
cycles, we can use "run cycles" if this is a per-task event, since the
processor is running when the task is running, by definition.  We
can't use "run cycles" if the user asks for "cycles" on a system-wide
counter.)

Fortunately the information we need is in the event->attach_state
field, so we just use that instead.

Signed-off-by: Paul Mackerras <paulus@...ba.org>
Reported-by: Alexey Kardashevskiy <aik@....ibm.com>
---
 arch/powerpc/kernel/perf_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c
index 9cb4924..3129c85 100644
--- a/arch/powerpc/kernel/perf_event.c
+++ b/arch/powerpc/kernel/perf_event.c
@@ -1092,7 +1092,7 @@ static int power_pmu_event_init(struct perf_event *event)
 	 * XXX we should check if the task is an idle task.
 	 */
 	flags = 0;
-	if (event->ctx->task)
+	if (event->attach_state & PERF_ATTACH_TASK)
 		flags |= PPMU_ONLY_COUNT_RUN;

 	/*
--
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