linux-kernel - Re: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression

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Message-ID: <20230529111859.GA15193@redhat.com>
Date:   Mon, 29 May 2023 13:19:39 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Christie <michael.christie@...cle.com>,
        linux@...mhuis.info, nicolas.dichtel@...nd.com, axboe@...nel.dk,
        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: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps
 regression

On 05/27, Eric W. Biederman wrote:
>
> Looking forward I don't see not asking the worker threads to stop
> for the coredump right now causing any problems in the future.
> So I think we can use this to resolve the coredump issue I spotted.

But we have almost the same problem with exec.

Execing thread will wait for vhost_worker() while vhost_worker will wait for
.release -> vhost_task_stop().

And even O_CLOEXEC won't help, do_close_on_exec() is called after de_thread().

Or suppose that vhost_worker's sub-thread forks a child with CLONE_FILES...

If we want CLONE_THREAD, I think vhost_worker() should exit after get_signal()
returns SIGKILL. Perhaps it should "disable" vhost_work_queue() somehow and
flush the pending works on ->work_list before exit, I dunno. But imo it should
not wait for the final fput().

Oleg.