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

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Message-ID: <Zo3bt3AJHSG5rVnZ@slm.duckdns.org>
Date: Tue, 9 Jul 2024 14:54:15 -1000
From: Tejun Heo <tj@...nel.org>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>, io-uring@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>,
	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 2/2] kernel: rerun task_work while freezing in
 get_signal()

Hello,

On Tue, Jul 09, 2024 at 08:55:43PM +0100, Pavel Begunkov wrote:
...
> > > CRIU, I assume. I'll try it ...
> > 
> > Than I think we can forget about task_works and this patch. CRIU dumps
> > the tasks in TASK_TRACED state.
> 
> And would be hard to test, io_uring (the main source of task_work)
> is not supported
> 
> (00.466022) Error (criu/proc_parse.c:477): Unknown shit 600 (anon_inode:[io_uring])
> ...
> (00.467642) Unfreezing tasks into 1
> (00.467656)     Unseizing 15488 into 1
> (00.468149) Error (criu/cr-dump.c:2111): Dumping FAILED.

Yeah, the question is: If CRIU is to use cgroup freezer to freeze the tasks
and then go around tracing each to make dump, would the freezer be enough in
avoiding interim state changes? Using CRIU implementation is a bit arbitrary
but I think checkpoint-restart is a useful bar to measure what should stay
stable while a cgroup is frozen.

Thanks.

-- 
tejun