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

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Message-ID: <20241122082407.GA14342@redhat.com>
Date: Fri, 22 Nov 2024 09:24:07 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
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

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.

> 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;
>
>