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

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Message-ID: <8cb29846-7e48-4308-ae4e-70b0e270dbb8@gmail.com>
Date: Wed, 10 Jul 2024 18:55:34 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Tejun Heo <tj@...nel.org>
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 7/10/24 01:57, Tejun Heo wrote:
> 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

I'll add a couple of words

> do_freezer_trap() instead of being integrated into the outer loop.

v1 had it in the common loop, but might actually be good it's
limited to freezing, need more digging.

-- 
Pavel Begunkov