Re: [tip:perf/core] perf: Fix race in perf_event_exec()

[Eric Dumazet]

On Wed, Jan 6, 2016 at 1:46 PM, tip-bot for Peter Zijlstra
<tipbot@xxxxxxxxx> wrote:

>
> This is because context switches can swap the task_struct::perf_event_ctxp[]
> pointer around. Therefore you have to either disable preemption when looking
> at current, or hold ctx->lock.
>


>
>  void perf_event_exec(void)
>  {
> -       struct perf_event_context *ctx;
>         int ctxn;
>
>         rcu_read_lock();

Do we still need this rcu_read_lock(), if perf_event_enable_on_exec()
uses  local_irq_save( ?

> -       for_each_task_context_nr(ctxn) {
> -               ctx = current->perf_event_ctxp[ctxn];
> -               if (!ctx)
> -                       continue;
> -
> -               perf_event_enable_on_exec(ctx);
> -       }
> +       for_each_task_context_nr(ctxn)
> +               perf_event_enable_on_exec(ctxn);
>         rcu_read_unlock();
>  }
>
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