Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 29 May 2023 13:19:39 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Mike Christie <michael.christie@oracle.com>,
        linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, mst@redhat.com,
        sgarzare@redhat.com, jasowang@redhat.com, stefanha@redhat.com,
        brauner@kernel.org
Subject: Re: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps
 regression
Message-ID: <20230529111859.GA15193@redhat.com>
References: <20230523121506.GA6562@redhat.com>
 <87bkib6nxr.fsf@email.froward.int.ebiederm.org>
 <20230524141022.GA19091@redhat.com>
 <87ttw1zt4i.fsf@email.froward.int.ebiederm.org>
 <20230525115512.GA9229@redhat.com>
 <87y1lcxwcj.fsf@email.froward.int.ebiederm.org>
 <CAHk-=wj4DS=2F5mW+K2P7cVqrsuGd3rKE_2k2BqnnPeeYhUCvg@mail.gmail.com>
 <87cz2mrtnk.fsf@email.froward.int.ebiederm.org>
 <CAHk-=whsi9JFP-okH3jXHrA8rh8bMuuSt6ZgkmPwiDMAn437qA@mail.gmail.com>
 <87mt1pmezu.fsf@email.froward.int.ebiederm.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <87mt1pmezu.fsf@email.froward.int.ebiederm.org>
User-Agent: Mutt/1.5.24 (2015-08-30)
Precedence: bulk

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.