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

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Date:   Mon, 29 May 2023 14:03:05 -0500
From:   Mike Christie <michael.christie@...cle.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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 5/29/23 12:54 PM, Oleg Nesterov wrote:
> On 05/29, Oleg Nesterov wrote:
>>
>> Mike, sorry, I don't understand your email.
>>
>> Just in case, let me remind I know nothing about drivers/vhost/
> 
> And... this is slightly off-topic but you didn't answer my previous
> question and I am just curious. Do you agree that, even if we forget
> about CLONE_THREAD/signals, vhost_worker() needs fixes anyway because
> it can race with vhost_work_queue() ?

You saw the reply where I wrote I was waiting for the vhost devs to
reply because it's their code, right? Just wanted to make sure you know
I'm not ignoring your mails. The info is very valuable to me since I don't
know the signal code.

- I think you are right about using a continue after schedule.
- The work fn is stable. It's setup once and never changes.
- I have no idea why we do the __set_current_state(TASK_RUNNING). As
far as I can tell the work functions do not change the task state and
that might have been a left over from something else. However, the
vhost devs might know of some case.
- For the barrier use, I think you are right, but I couldn't trigger
an issue even if I hack up different timings. So I was hoping the
vhost devs know of something else in there.