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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 13 May 2023 10:08:04 -0500
Message-ID: <CAHk-=wicXCNR1bBioaAiBqEDgv-CoQD9z2RsM2VOTPzkK0xr8g@mail.gmail.com>
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads
To:     Thorsten Leemhuis <linux@leemhuis.info>
Cc:     Mike Christie <michael.christie@oracle.com>,
        nicolas.dichtel@6wind.com, Christian Brauner <brauner@kernel.org>,
        Linux kernel regressions list <regressions@lists.linux.dev>,
        hch@infradead.org, stefanha@redhat.com, jasowang@redhat.com,
        mst@redhat.com, sgarzare@redhat.com,
        virtualization@lists.linux-foundation.org, ebiederm@xmission.com,
        konrad.wilk@oracle.com, linux-kernel@vger.kernel.org
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On Sat, May 13, 2023 at 7:39=E2=80=AFAM Thorsten Leemhuis <linux@leemhuis.i=
nfo> 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 |=3D 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