Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Thorsten Leemhuis <linux@leemhuis.info>
Cc: Christian Brauner <brauner@kernel.org>,
	Linux kernel regressions list <regressions@lists.linux.dev>,
	mst@redhat.com, konrad.wilk@oracle.com,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org, hch@infradead.org,
	ebiederm@xmission.com, stefanha@redhat.com,
	nicolas.dichtel@6wind.com
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads
Date: Sat, 13 May 2023 10:08:04 -0500	[thread overview]
Message-ID: <CAHk-=wicXCNR1bBioaAiBqEDgv-CoQD9z2RsM2VOTPzkK0xr8g@mail.gmail.com> (raw)
In-Reply-To: <48842e92-835e-bc3f-7118-48b8f415f532@leemhuis.info>

On Sat, May 13, 2023 at 7:39 AM Thorsten Leemhuis <linux@leemhuis.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
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