linux-kernel - Re: [patch V5 16/26] signal: Replace resched

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Message-ID: <ZyEOeqkSYWR2XTp_@localhost.localdomain>
Date: Tue, 29 Oct 2024 17:34:02 +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 V5 16/26] signal: Replace resched_timer logic

Le Tue, Oct 29, 2024 at 05:22:17PM +0100, Thomas Gleixner a écrit :
> On Tue, Oct 29 2024 at 16:56, Frederic Weisbecker wrote:
> >> @@ -568,10 +568,10 @@ static void collect_signal(int sig, stru
> >>  		list_del_init(&first->list);
> >>  		copy_siginfo(info, &first->info);
> >>  
> >> -		*resched_timer = (first->flags & SIGQUEUE_PREALLOC) &&
> >> -				 (info->si_code == SI_TIMER);
> >> -
> >> -		__sigqueue_free(first);
> >> +		if (unlikely((first->flags & SIGQUEUE_PREALLOC) && (info->si_code == SI_TIMER)))
> >> +			*timer_sigq = first;
> >> +		else
> >> +			__sigqueue_free(first);
> >
> > So this isn't calling __sigqueue_free() unconditionally anymore. What if
> > the timer has been freed already, what is going to free the sigqueue?
> 
> __sigqueue_free() does not free timers marked with SIGQUEUE_PREALLOC.
> 
> sigqueue_free() takes care of that, which is invoked from
> posixtimer_free_timer(). It clears SIGQUEUE_PREALLOC and if it is queued
> it lets it pending and delivery will free it.

But the delivery freeing used to be done with the __sigqueue_free()
above, which doesn't happen anymore, right?

> 
> That's not any different from before this change.
> 
> Though thinking more about it. As we drop the signal in that case
> anyway, we could remove it from pending in sigqueue_free() directly. Let
> me look into that.

Ok.

Thanks.

> 
> Thanks,
> 
>         tglx