linux-kernel - Re: [patch v6 17/20] signal: Queue ignored posixtimers on ignore list

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Message-ID: <ZyTj2W8Jndv0nzga@localhost.localdomain>
Date: Fri, 1 Nov 2024 15:21:13 +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>,
	John Stultz <jstultz@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
	Eric Biederman <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [patch v6 17/20] signal: Queue ignored posixtimers on ignore list

Le Thu, Oct 31, 2024 at 04:46:43PM +0100, Thomas Gleixner a écrit :
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Queue posixtimers which have their signal ignored on the ignored list:
> 
>    1) When the timer fires and the signal has SIG_IGN set
> 
>    2) When SIG_IGN is installed via sigaction() and a timer signal
>       is already queued
> 
> This completes the SIG_IGN handling and such timers are not longer self
> rearmed which avoids pointless wakeups.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/signal.c |   39 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 34 insertions(+), 5 deletions(-)
> ---
> 
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -731,6 +731,16 @@ void signal_wake_up_state(struct task_st
>  		kick_process(t);
>  }
>  
> +static inline void posixtimer_sig_ignore(struct task_struct *tsk, struct sigqueue *q);
> +
> +static void sigqueue_free_ignored(struct task_struct *tsk, struct sigqueue *q)
> +{
> +	if (likely(!(q->flags & SIGQUEUE_PREALLOC) || q->info.si_code != SI_TIMER))
> +		__sigqueue_free(q);
> +	else
> +		posixtimer_sig_ignore(tsk, q);

So this happens when the signal is ignored and delays it to when it will be
unignored. But the comment on do_sigaction() says:

		/*
		 * POSIX 3.3.1.3:
		 *  "Setting a signal action to SIG_IGN for a signal that is
		 *   pending shall cause the pending signal to be discarded,
		 *   whether or not it is blocked."
		 *
		 */

Are posix timers an exception to that rule?

Also I see flush_sigqueue_mask() called on other occasions, for example
when a STOP signal happens to remove pending CONT, not sure if posix
timers can set SIGCONT...

Thanks.