Re: [PATCH v3 06/11] perf: Add support for SIGTRAP on perf events

[Peter Zijlstra]

On Mon, Mar 29, 2021 at 04:32:18PM +0200, Marco Elver wrote:
> On Mon, 29 Mar 2021 at 16:27, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > On 03/29, Peter Zijlstra wrote:
> > >
> > > On Thu, Mar 25, 2021 at 09:14:39AM +0100, Marco Elver wrote:
> > > > @@ -6395,6 +6395,13 @@ static void perf_sigtrap(struct perf_event *event)
> > > >  {
> > > >     struct kernel_siginfo info;
> > > >
> > > > +   /*
> > > > +    * This irq_work can race with an exiting task; bail out if sighand has
> > > > +    * already been released in release_task().
> > > > +    */
> > > > +   if (!current->sighand)
> > > > +           return;
> >
> > This is racy. If "current" has already passed exit_notify(), current->parent
> > can do release_task() and destroy current->sighand right after the check.
> >
> > > Urgh.. I'm not entirely sure that check is correct, but I always forget
> > > the rules with signal. It could be we ought to be testing PF_EXISTING
> > > instead.
> >
> > Agreed, PF_EXISTING check makes more sense in any case, the exiting task
> > can't receive the signal anyway.
> 
> Thanks for confirming. I'll switch to just checking PF_EXITING
> (PF_EXISTING does not exist :-)).

Indeed! Typing be hard :-)