Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx value

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2011-03-28 at 16:57 +0200, Peter Zijlstra wrote:
> 
> ---
> Subject: perf: Optimize ctx_sched_out
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Mon Mar 28 16:55:36 CEST 2011
> 
> Oleg noted that ctx_sched_out() disables the PMU even though it might
> not actually do something, avoid needless PMU-disabling.
> 
> Reported-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> LKML-Reference: <new-submission>
> ---
>  kernel/perf_event.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/kernel/perf_event.c
> ===================================================================
> --- linux-2.6.orig/kernel/perf_event.c
> +++ linux-2.6/kernel/perf_event.c
> @@ -1767,7 +1767,6 @@ static void ctx_sched_out(struct perf_ev
>         struct perf_event *event;
>  
>         raw_spin_lock(&ctx->lock);
> -       perf_pmu_disable(ctx->pmu);
>         ctx->is_active = 0;
>         if (likely(!ctx->nr_events))
>                 goto out;
> @@ -1777,6 +1776,7 @@ static void ctx_sched_out(struct perf_ev
>         if (!ctx->nr_active)
>                 goto out;
>  
> +       perf_pmu_disable(ctx->pmu);
>         if (event_type & EVENT_PINNED) {
>                 list_for_each_entry(event, &ctx->pinned_groups, group_entry)
>                         group_sched_out(event, cpuctx, ctx);
> @@ -1786,8 +1786,8 @@ static void ctx_sched_out(struct perf_ev
>                 list_for_each_entry(event, &ctx->flexible_groups, group_entry)
>                         group_sched_out(event, cpuctx, ctx);
>         }
> -out:
>         perf_pmu_enable(ctx->pmu);
> +out:
>         raw_spin_unlock(&ctx->lock);
>  }

We could probably remove the PMU disabling all together, but that would
involve like actual thinking :-)