Messages in this thread | | | Date | Mon, 28 Mar 2011 15:30:33 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx value |
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On 03/26, Peter Zijlstra wrote: > > 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.
Wait... Yes, we have to clear ctx->is_active, otherwise we break, say, perf_install_in_context().
But if we clear ->is_active we break perf_event_enable(). Suppose we are doing ioctl(PERF_EVENT_IOC_DISABLE) + ioctl(PERF_EVENT_IOC_ENABLE). PERF_EVENT_IOC_DISABLE can sched_out the last event, but _IOC_ENABLE treats ctx->is_active == F as "it is not running".
Btw, why ctx_sched_out() checks nr_events under perf_pmu_disable() ?
Oleg.
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