linux-kernel - Re: posix timer freeze after some random time, under pthread create/destroy load

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Message-ID: <Z0BliWkMHHzohMt3@pavilion.home>
Date: Fri, 22 Nov 2024 12:05:45 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Anthony Mallet <anthony.mallet@...s.fr>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
	Marco Elver <elver@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: posix timer freeze after some random time, under pthread
 create/destroy load

Le Fri, Nov 22, 2024 at 09:24:07AM +0100, Oleg Nesterov a écrit :
> On 11/21, Frederic Weisbecker wrote:
> >
> > I think this started with commit:
> >
> > bcb7ee79029d (posix-timers: Prefer delivery of signals to the current thread)
> >
> > The problem is that if the current task is exiting and has already been reaped,
> > its sighand pointer isn't there anymore.
> 
> Thanks...
> 
> This can only happen if the exiting task has already passed exit_notify() which
> sets exit_state. So I'd suggest to check current->exit_state instead of PF_EXITING
> in the patch below.
> 
> Oleg.

Right, I don't mind either way, though if it's past PF_EXITING,
complete_signal() -> wants_signal() will defer to another thread anyway, right?
Due to retarget_shared_pending() being called after the flag being set...

Thanks.

> 
> > And so the signal is ignored even
> > though it should be queued to and handled by the thread group that has other
> > live threads to take care of it.
> >
> > Can you test the following patch? I'm cooking another patch with changelog for
> > upstream that has seen recent changes in this area.
> >
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index 8f6330f0e9ca..4cadee618d4b 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -1984,7 +1984,8 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
> >  	t = pid_task(pid, type);
> >  	if (!t)
> >  		goto ret;
> > -	if (type != PIDTYPE_PID && same_thread_group(t, current))
> > +	if (type != PIDTYPE_PID && same_thread_group(t, current) &&
> > +	    !(current->flags & PF_EXITING))
> >  		t = current;
> >  	if (!likely(lock_task_sighand(t, &flags)))
> >  		goto ret;
> >
> >
>