linux-kernel - Re: [CFT][PATCH v3] fork, vhost: Use CLONE

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Date:   Wed, 14 Jun 2023 19:08:04 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Mike Christie <michael.christie@...cle.com>, linux@...mhuis.info,
        nicolas.dichtel@...nd.com, axboe@...nel.dk,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        sgarzare@...hat.com, jasowang@...hat.com, stefanha@...hat.com,
        brauner@...nel.org
Subject: Re: [CFT][PATCH v3] fork, vhost: Use CLONE_THREAD to fix freezer/ps
 regression

On 06/11, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > Could you spell to explain why this can't work (again, in this simple case) ?
> >
> > My current (and I know, very poor) understanding is that .release() should
> > roughly do the following:
> >
> > 	1. Ensure that vhost_work_queue() can't add the new callbacks
> >
> > 	2. Call vhost_dev_flush() to ensure that worker->work_list is empty
> >
> > 	3. Call vhost_task_stop()
>
> At least in the case of exec by the time the final fput happens
> from close_on_exec the task has already changed it's mm.

Of course you are right.

But can't resist, please note that I only meant "this simple case" which
doesn't include exec/etc.

Nevermind. As Mike explains there are more problems even in this particular
"simple" case, and I am not surprised.

Sorry for noise,

Oleg.