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SubjectRe: [PATCH] perf, powerpc: Fix power_pmu_event_init to not use event->ctx
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On Tue, 2010-10-19 at 16:55 +1100, Paul Mackerras wrote:
> 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.

Ah, sorry for the breakage.

> Signed-off-by: Paul Mackerras <paulus@samba.org>
> Reported-by: Alexey Kardashevskiy <aik@au1.ibm.com>

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> ---
> 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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