linux-kernel - Re: [PATCH v11 8/8] vhost: use vhost

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Date:   Sat, 13 May 2023 10:08:04 -0500
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thorsten Leemhuis <linux@...mhuis.info>
Cc:     Mike Christie <michael.christie@...cle.com>,
        nicolas.dichtel@...nd.com, Christian Brauner <brauner@...nel.org>,
        Linux kernel regressions list <regressions@...ts.linux.dev>,
        hch@...radead.org, stefanha@...hat.com, jasowang@...hat.com,
        mst@...hat.com, sgarzare@...hat.com,
        virtualization@...ts.linux-foundation.org, ebiederm@...ssion.com,
        konrad.wilk@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads

On Sat, May 13, 2023 at 7:39 AM Thorsten Leemhuis <linux@...mhuis.info> wrote:
>
> Jumping in here, as I found another problem with that patch: it broke
> s2idle on my laptop when a qemu-kvm VM is running, as freezing user
> space processes now fails for me:

Hmm. kthreads have PF_NOFREEZE by default, which is probably the reason.

Adding

        current->flags |= PF_NOFREEZE;

to the vhost_task setup might just fix it, but it feels a bit off.

The way io_uring does this is to  do

                if (signal_pending(current)) {
                        struct ksignal ksig;

                        if (!get_signal(&ksig))
                                continue;
                        break;
                }

in the main loop, which ends up handling the freezer situation too.
But it should handle things like SIGSTOP etc as well, and also exit on
actual signals.

I get the feeling that the whole "vhost_task_should_stop()" logic
should have the exact logic above, and basically make those threads
killable as well.

Hmm?

                Linus