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

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Date:   Thu, 25 May 2023 13:55:13 +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: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps
 regression

On 05/24, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > Yes, but probably SIGABRT/exit doesn't really differ from SIGKILL wrt
> > vhost_worker().
>
> Actually I think it reveals that exiting with SIGABRT will cause
> a deadlock.
>
> coredump_wait will wait for all of the threads to reach
> coredump_task_exit.  Meanwhile vhost_worker is waiting for
> all of the other threads to reach exit_files to close their
> file descriptors.

Indeed, I didn't think about this.


So why do we actually need CLONE_THREAD ? Can't vhost_worker() be a kernel thread?

kthread_create() won't be convenient, but how about kernel_thread() ? it inherits
mm/cgroups/rlimits/etc, kthread_stop() should work just fine.

Oleg.