Re: [PATCH 09/10] kthread: Ensure struct kthread is present for all kthreads

[Eric W. Biederman]

Added a couple of people from the vhost thread.

Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:

> On Wed, Dec 22, 2021 at 3:25 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> 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