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

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Date:   Sat, 27 May 2023 20:41:29 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Mike Christie <michael.christie@...cle.com>
Cc:     Oleg Nesterov <oleg@...hat.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

Mike Christie <michael.christie@...cle.com> writes:

> On 5/23/23 7:15 AM, Oleg Nesterov wrote:
>> 
>> Now the main question. Whatever we do, SIGKILL/SIGSTOP/etc can come right
>> before we call work->fn(). Is it "safe" to run this callback with
>> signal_pending() or fatal_signal_pending() ?
>
> The questions before this one I'll leave for the core vhost devs since
> they know best.

Let me ask a clarifying question:

Is it only the call to schedule() in vhost_worker that you are worried
about not sleeping if signal_pending() or fatal_signal_pending()?

Is there concern that the worker functions aka "work->fn()" will also
have killable or interruptible sleeps that also will misbehave.

We can handle schedule() in vhost_worker without problem.

If a worker function has interruptible or killable sleeps that will turn
into busy waits or worse not sleeping long enough that seems like a
problem.  There is no way to guarantee that the outer loop of
vhost_worker will protect the worker functions from signal_pending()
or fatal_signal_pending() becoming true.

Eric