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

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Jan 06, 2016 at 01:56:56PM -0500, Eric Dumazet wrote:
> On Wed, Jan 6, 2016 at 1:46 PM, tip-bot for Peter Zijlstra
> <tipbot@zytor.com> 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( ?

Strictly speaking we should not rely on the fact that RCU grace periods
do not progress with IRQs disabled, so yes.