linux-kernel - Re: [RFC PATCH 0/8] vhost_tasks: Use CLONE

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Message-ID: <2ccdf297-0998-d1a8-5a66-0abdc6e37c1b@oracle.com>
Date:   Thu, 1 Jun 2023 11:10:50 -0500
From:   Mike Christie <michael.christie@...cle.com>
To:     Christian Brauner <brauner@...nel.org>,
        Thorsten Leemhuis <linux@...mhuis.info>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     oleg@...hat.com, nicolas.dichtel@...nd.com, axboe@...nel.dk,
        ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        sgarzare@...hat.com, jasowang@...hat.com, stefanha@...hat.com,
        Linux kernel regressions list <regressions@...ts.linux.dev>,
        hch@...radead.org, konrad.wilk@...cle.com
Subject: Re: [RFC PATCH 0/8] vhost_tasks: Use CLONE_THREAD/SIGHAND

On 6/1/23 5:47 AM, Christian Brauner wrote:
> On Thu, Jun 01, 2023 at 09:58:38AM +0200, Thorsten Leemhuis wrote:
>> On 19.05.23 14:15, Christian Brauner wrote:
>>> On Thu, May 18, 2023 at 10:25:11AM +0200, Christian Brauner wrote:
>>>> On Wed, May 17, 2023 at 07:09:12PM -0500, Mike Christie wrote:
>>>>> This patch allows the vhost and vhost_task code to use CLONE_THREAD,
>>>>> CLONE_SIGHAND and CLONE_FILES. It's a RFC because I didn't do all the
>>>>> normal testing, haven't coverted vsock and vdpa, and I know you guys
>>>>> will not like the first patch. However, I think it better shows what
>>>> Just to summarize the core idea behind my proposal is that no signal
>>>> handling changes are needed unless there's a bug in the current way
>>>> io_uring workers already work. All that should be needed is
>>>> s/PF_IO_WORKER/PF_USER_WORKER/ in signal.c.
>> [...]
>>>> So it feels like this should be achievable by adding a callback to
>>>> struct vhost_worker that get's called when vhost_worker() gets SIGKILL
>>>> and that all the users of vhost workers are forced to implement.
>>>>
>>>> Yes, it is more work but I think that's the right thing to do and not to
>>>> complicate our signal handling.
>>>>
>>>> Worst case if this can't be done fast enough we'll have to revert the
>>>> vhost parts. I think the user worker parts are mostly sane and are
>>> As mentioned, if we can't settle this cleanly before -rc4 we should
>>> revert the vhost parts unless Linus wants to have it earlier.
>> Meanwhile -rc5 is just a few days away and there are still a lot of
>> discussions in the patch-set proposed to address the issues[1]. Which is
>> kinda great (albeit also why I haven't given it a spin yet), but on the
>> other hand makes we wonder:
> You might've missed it in the thread but it seems everyone is currently
> operating under the assumption that the preferred way is to fix this is
> rather than revert. See the mail in [1]:
> 
> "So I'd really like to finish this. Even if we end up with a hack or
> two in signal handling that we can hopefully fix up later by having
> vhost fix up some of its current assumptions."
> 
> which is why no revert was send for -rc4. And there's a temporary fix we
> seem to have converged on.
> 
> @Mike, do you want to prepare an updated version of the temporary fix.
> If @Linus prefers to just apply it directly he can just grab it from the
> list rather than delaying it. Make sure to grab a Co-developed-by line
> on this, @Mike.

Yes, I'll send it within a couple hours.