From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Alexey Gladkov <legion@kernel.org>,
        Kyle Huey <me@kylehuey.com>, Oleg Nesterov <oleg@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Mike Christie <michael.christie@oracle.com>,
        Mike Christie <michael.christie@oracle.com>,
        virtualization@lists.linux-foundation.org,
        christian.brauner@ubuntu.com, axboe@kernel.dk
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Date:   Wed, 22 Dec 2021 21:34:39 -0600
In-Reply-To: <CAHk-=wgtFAA9SbVYg0gR1tqPMC17-NYcs0GQkaYg1bGhh1uJQQ@mail.gmail.com>
        (Linus Torvalds's message of "Wed, 22 Dec 2021 17:44:19 -0800")
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Subject: Re: [PATCH 09/10] kthread: Ensure struct kthread is present for all kthreads
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Added a couple of people from the vhost thread.

Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Wed, Dec 22, 2021 at 3:25 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>>
>> Solve this by skipping the put_user for all kthreads.
>
> Ugh.
>
> While this fixes the problem, could we please just not mis-use that
> 'set_child_tid' as that kthread pointer any more?
>
> It was always kind of hacky. I think a new pointer with the proper
> 'struct kthread *' type would be an improvement.
>
> One of the "arguments" in the comment for re-using that set_child_tid
> pointer was that 'fork()' used to not wrongly copy it, but your patch
> literally now does that "allocate new kthread struct" at fork-time, so
> that argument is actually bogus now.

I agree.  I think I saw in the recent vhost patches that were
generalizing create_io_thread that the pf_io_worker field of
struct task_struct was being generalized as well.

If so I think it makes sense just to take that approach.

Just build some basic infrastructure that can be used for io_workers,
vhost_workers, and kthreads.

Eric