linux-kernel - Re: [PATCH v2 2/2] kernel: rerun task_work while freezing in get

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Message-ID: <Zo3cdEMZVOJcseWm@slm.duckdns.org>
Date: Tue, 9 Jul 2024 14:57:24 -1000
From: Tejun Heo <tj@...nel.org>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christian Brauner <brauner@...nel.org>,
	Tycho Andersen <tandersen@...flix.com>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Julian Orth <ju.orth@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 2/2] kernel: rerun task_work while freezing in
 get_signal()

On Tue, Jul 09, 2024 at 03:27:19PM +0100, Pavel Begunkov wrote:
> io_uring can asynchronously add a task_work while the task is getting
> freezed. TIF_NOTIFY_SIGNAL will prevent the task from sleeping in
> do_freezer_trap(), and since the get_signal()'s relock loop doesn't
> retry task_work, the task will spin there not being able to sleep
> until the freezing is cancelled / the task is killed / etc.
> 
> Cc: stable@...r.kernel.org
> Link: https://github.com/systemd/systemd/issues/33626
> Fixes: 12db8b690010c ("entry: Add support for TIF_NOTIFY_SIGNAL")
> Reported-by: Julian Orth <ju.orth@...il.com>
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>

I haven't looked at the signal code for too long to be all that useful but
the problem described and the patch does make sense to me. FWIW,

Acked-by: Tejun Heo <tj@...nel.org>

Maybe note that this is structured specifically to ease backport and we need
further cleanups? It's not great that this is special cased in
do_freezer_trap() instead of being integrated into the outer loop.

Thanks.

-- 
tejun