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SubjectRe: Q: perf_install_in_context/perf_event_enable are racy?
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On Fri, 2011-01-21 at 14:03 +0100, Ingo Molnar wrote:
> > > But, it seems, there is another problem. Forget about the exiting,
> > > I can't understand why we can trust current in the code above.
> > > With __ARCH_WANT_INTERRUPTS_ON_CTXSW schedule() does:
> > >
> > > // sets cpuctx->task_ctx = NULL
> > > perf_event_task_sched_out();
> > >
> > > // enables irqs
> > > prepare_lock_switch();
> > >
> > >
> > > // updates current_task
> > > switch_to();
> > >
> > > What if IPI comes in the window before switch_to() ?
> > >
> > > (the same questions for __perf_event_enable).
> >
> > Ingo, do you have any insights in that, I think you wrote all that
> > initially?
>
> Not sure. Can an IPI come there - we have irqs disabled usually, dont we?

Ah, I think I see how that works:

__perf_event_task_sched_out()
perf_event_context_sched_out()
if (do_switch)
cpuctx->task_ctx = NULL;
vs

__perf_install_in_context()
if (cpu_ctx->task_ctx != ctx)



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