linux-kernel - Re: [patch V5 05/26] posix-timers: Drop signal if timer has been deleted or reprogrammed

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Message-ID: <ZxZJPnqsQygi6juI@localhost.localdomain>
Date: Mon, 21 Oct 2024 14:29:50 +0200
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 V5 05/26] posix-timers: Drop signal if timer has been
 deleted or reprogrammed

Le Tue, Oct 01, 2024 at 10:42:06AM +0200, Thomas Gleixner a écrit :
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> No point in delivering a signal from the past. POSIX does not specify the
> behaviour here:
> 
>  - "The effect of disarming or resetting a timer with pending expiration
>     notifications is unspecified."
> 
>  - "The disposition of pending signals for the deleted timer is unspecified."
> 
> In both cases it is reasonable to expect that pending signals are
> discarded. Especially in the reprogramming case it does not make sense to
> account for previous overruns or to deliver a signal for a timer which has
> been disarmed.

The change below indeed checks if the timer has been deleted but not if
it has been reprogrammed/disarmed/reset.

Or am I missing something?

Thanks.

> 
> Drop the signal as that is conistent and understandable behaviour.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/time/posix-timers.c |  9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> ---
> diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
> index d7ed7542f803..b5d7e71c10f2 100644
> --- a/kernel/time/posix-timers.c
> +++ b/kernel/time/posix-timers.c
> @@ -250,14 +250,14 @@ static void common_hrtimer_rearm(struct k_itimer *timr)
>  }
>  
>  /*
> - * This function is called from the signal delivery code if
> - * info::si_sys_private is not zero, which indicates that the timer has to
> - * be rearmed. Restart the timer and update info::si_overrun.
> + * This function is called from the signal delivery code. It decides
> + * whether the signal should be dropped and rearms interval timers.
>   */
>  bool posixtimer_deliver_signal(struct kernel_siginfo *info)
>  {
>  	struct k_itimer *timr;
>  	unsigned long flags;
> +	bool ret = false;
>  
>  	/*
>  	 * Release siglock to ensure proper locking order versus
> @@ -279,6 +279,7 @@ bool posixtimer_deliver_signal(struct kernel_siginfo *info)
>  
>  		info->si_overrun = timer_overrun_to_int(timr, info->si_overrun);
>  	}
> +	ret = true;
>  
>  	unlock_timer(timr, flags);
>  out:
> @@ -286,7 +287,7 @@ bool posixtimer_deliver_signal(struct kernel_siginfo *info)
>  
>  	/* Don't expose the si_sys_private value to userspace */
>  	info->si_sys_private = 0;
> -	return true;
> +	return ret;
>  }
>  
>  int posix_timer_queue_signal(struct k_itimer *timr)
>