linux-kernel - Re: [patch V2 08/17] posix-timers: Rework timer removal

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Message-ID: <Z8zJQtzLIliTNe2e@pavilion.home>
Date: Sat, 8 Mar 2025 23:48:34 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Benjamin Segall <bsegall@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch V2 08/17] posix-timers: Rework timer removal

Le Sat, Mar 08, 2025 at 09:34:06AM +0100, Thomas Gleixner a écrit :
> On Sat, Mar 08 2025 at 00:03, Frederic Weisbecker wrote:
> > Le Sun, Mar 02, 2025 at 08:36:56PM +0100, Thomas Gleixner a écrit :
> >> --- a/include/linux/posix-timers.h
> >> +++ b/include/linux/posix-timers.h
> >> @@ -240,6 +240,13 @@ static inline void posixtimer_sigqueue_p
> >>  
> >>  	posixtimer_putref(tmr);
> >>  }
> >> +
> >> +static inline bool posixtimer_valid(const struct k_itimer *timer)
> >> +{
> >> +	unsigned long val = (unsigned long)timer->it_signal;
> >> +
> >> +	return !(val & 0x1UL);
> >> +}
> >>  #else  /* CONFIG_POSIX_TIMERS */
> >>  static inline void posixtimer_sigqueue_getref(struct sigqueue *q) { }
> >>  static inline void posixtimer_sigqueue_putref(struct sigqueue *q) { }
> >> --- a/kernel/signal.c
> >> +++ b/kernel/signal.c
> >> @@ -2092,7 +2092,7 @@ static inline void posixtimer_sig_ignore
> >>  	 * from a non-periodic timer, then just drop the reference
> >>  	 * count. Otherwise queue it on the ignored list.
> >>  	 */
> >> -	if (tmr->it_signal && tmr->it_sig_periodic)
> >> +	if (posixtimer_valid(tmr) && tmr->it_sig_periodic)
> >>  		hlist_add_head(&tmr->ignored_list, &tsk->signal->ignored_posix_timers);
> >>  	else
> >>  		posixtimer_putref(tmr);
> >> --- a/kernel/time/posix-timers.c
> >> +++ b/kernel/time/posix-timers.c
> >> @@ -279,7 +279,7 @@ static bool __posixtimer_deliver_signal(
> >>  	 * since the signal was queued. In either case, don't rearm and
> >>  	 * drop the signal.
> >>  	 */
> >> -	if (timr->it_signal_seq != timr->it_sigqueue_seq || WARN_ON_ONCE(!timr->it_signal))
> >> +	if (timr->it_signal_seq != timr->it_sigqueue_seq || !posixtimer_valid(timr))
> >
> > Hmm, should it still warn here? ie: WARN_ON_ONCE(!posixtimer_valid(timr)) ?
> 
> No, because the timer is invalidated early now.

But the signal can only be queued before posix_timer_delete(). So
if the bit 0 of it_signal has been reset, it_signal_seq must have been
incremented along, right?

And if so then timr->it_signal_seq == timr->it_sigqueue_seq must imply
posixtimer_valid(). And if not we should warn. Or am I missing something?

Thanks.


> 
> Thanks,
> 
>         tglx