Re: [PATCH 2/4] task_work: don't run task_work if task_work_exited is queued

[Oleg Nesterov <oleg@redhat.com>]

On 04/07, Jens Axboe wrote:
>
> On 4/7/20 4:39 AM, Oleg Nesterov wrote:
> >
> > IIUC, this is needed for the next change which adds task_work_run() into
> > io_ring_ctx_wait_and_kill(), right?
>
> Right - so you'd rather I localize that check there instead? Can certainly
> do that.

I am still not sure we need this check at all... probably this is because
I don't understand the problem.

> > could you explain how the exiting can call io_ring_ctx_wait_and_kill()
> > after it passed exit_task_work() ?
>
> Sure, here's a trace where it happens:

but this task has not passed exit_task_work(),

>  __task_work_run+0x66/0xa0
>  io_ring_ctx_wait_and_kill+0x14e/0x3c0
>  io_uring_release+0x1c/0x20
>  __fput+0xaa/0x200
>  __task_work_run+0x66/0xa0
>  do_exit+0x9cf/0xb40

So task_work_run() is called recursively from exit_task_work()->task_work_run().
See my another email, this is wrong with or without this series. And that is
why I think task_work_run() hits work_exited.

Could you explain why io_ring_ctx_wait_and_kill() needs task_work_run() ?

Oleg.