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Message-ID: <ZyFDIP_1zeygVxa8@pavilion.home>
Date: Tue, 29 Oct 2024 21:18:40 +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 08:16:27PM +0100, Thomas Gleixner a écrit :
> On Tue, Oct 29 2024 at 18:55, Frederic Weisbecker wrote:
> > Le Tue, Oct 29, 2024 at 05:55:38PM +0100, Thomas Gleixner a écrit :
> >> It still happens because SIGQUEUE_PREALLOC is cleared in sigqueue_free()
> >>
> >> __sigqueue_free() has
> >> if (q->flags & PREALLOC)
> >> return;
> >>
> >> So the old code called __sigqueue_free() unconditionally which just
> >> returned. But now we have a condition to that effect already, so why
> >> call into __sigqueue_free() for nothing?
> >
> > 1) Signal is queued
> > 2) Timer is deleted, sigqueue() clears SIGQUEUE_PREALLOC but doesn't go
> > further because the sigqueue is queued
> > 3) Signal is collected and delivered but it's not calling __sigqueue_free()
> > so the sigqueue is not released.
> >
> > This is "fixed" on the subsequent patch which uses embedded sigqueue and
> > rcuref but this patch alone breaks.
> >
> > Or am I missing something that prevents it?
>
> Again:
>
> > 1) Signal is queued
> > 2) Timer is deleted, sigqueue() clears SIGQUEUE_PREALLOC but doesn't go
> > further because the sigqueue is queued
>
> 3)
>
> void collect_signal(..)
>
> if (unlikely((first->flags & SIGQUEUE_PREALLOC) && (info->si_code == SI_TIMER)))
> *timer_sigq = first; // Path NOT taken because SIGQUEUE_PREALLOC is not set
> else
> __sigqueue_free(first); // Path taken and frees it
>
> No?
Duh! Yes of course...
Thanks.
>
> Thanks,
>
> tglx
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