Messages in this thread | | | Subject | Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx value | From | Peter Zijlstra <> | Date | Sat, 26 Mar 2011 19:29:28 +0100 |
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On Sat, 2011-03-26 at 18:35 +0100, Oleg Nesterov wrote: > On 03/26, Oleg Nesterov wrote: > > > > On 03/26, Peter Zijlstra wrote: > > > > > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > > > index c75925c..e9e4e35 100644 > > > --- a/kernel/perf_event.c > > > +++ b/kernel/perf_event.c > > > @@ -1073,6 +1073,8 @@ event_sched_out(struct perf_event *event, > > > if (!is_software_event(event)) > > > cpuctx->active_oncpu--; > > > ctx->nr_active--; > > > + if (!ctx->nr_active && cpuctx->task_ctx == ctx) > > > + cpuctx->task_ctx = NULL; > > > > If we clear cpuctx->task_ctx, we should also clear ctx->is_active.
Right.
> > Otherwise I can't see any problem, but I do not understand this code > > enough. > > but probably we also need update_context_time().
It looks like event_sched_out() relies on up-to-date ctx->time through perf_event_time() and most call-paths leading to event_sched_out() do indeed seem to update the ctx time, all except the move_group branch in perf_event_open() afaict.
Sadly the reproducer doesn't seem to trigger the issue at all, its still running on a plain -tip kernel.
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