Re: [patch 04/44] posix-cpu-timers: Fixup stale comment

Thomas Gleixner
2019-08-20T17:57:43Z

On Tue, 20 Aug 2019, Frederic Weisbecker wrote:
> On Mon, Aug 19, 2019 at 04:31:45PM +0200, Thomas Gleixner wrote:
> > /*
> > - * Clean out CPU timers still ticking when a thread exited. The task
> > - * pointer is cleared, and the expiry time is replaced with the residual
> > - * time for later timer_gettime calls to return.
> > + * Clean out CPU timers which are still armed when a thread exits. The
> > + * timers are only removed from the list. No other updates are done. The
> > + * corresponding posix timers are still accessible, but cannot be rearmed.
> > + *
> > * This must be called with the siglock held.
> > */
> > static void cleanup_timers(struct list_head *head)
>
> Indeed and I believe we could avoid that step. We remove the sighand at the same
> time so those can't be accessed anymore anyway.
>
> exit_itimers() takes care of the last call release and could force remove from
> the list (although it might be taken care of in your series, haven't checked yet):

No. The posix timer is not necessarily owned by the exiting task or
process. It can be owned by a different entity which has permissions,
e.g. parent.

So those are not in the posix timer list of the exiting task, which gets
cleaned up in exit_itimers(). Those are in the list of the task which armed
the timer. The timer is merily queued in the 'active timers' list of the
exiting task and posix_cpu_timers_exit()/posix_cpu_timers_exit_group()
remove it before the task/signal structs go away.

Thanks,

tglx