Re: [PATCH] io_uring: run normal task_work AFTER local work

[Jan Hendrik Farr <kernel@jfarr.cc>]

On 19 12:06:20, Jens Axboe wrote:
> On 9/19/24 10:47 AM, Jan Hendrik Farr wrote:
> >> [...]
> >>
> >> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> >> index 75f0087183e5..56097627eafc 100644
> >> --- a/io_uring/io_uring.c
> >> +++ b/io_uring/io_uring.c
> >> @@ -2472,7 +2472,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
> >>  		return 1;
> >>  	if (unlikely(!llist_empty(&ctx->work_llist)))
> >>  		return 1;
> >> -	if (unlikely(test_thread_flag(TIF_NOTIFY_SIGNAL)))
> >> +	if (unlikely(task_work_pending(current)))
> >>  		return 1;
> >>  	if (unlikely(task_sigpending(current)))
> >>  		return -EINTR;
> >> diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
> >> index 9d70b2cf7b1e..2fbf0ea9c171 100644
> >> --- a/io_uring/io_uring.h
> >> +++ b/io_uring/io_uring.h
> >> @@ -308,15 +308,17 @@ static inline int io_run_task_work(void)
> >>  	 */
> >>  	if (test_thread_flag(TIF_NOTIFY_SIGNAL))
> >>  		clear_notify_signal();
> >> +
> >> +	if (test_thread_flag(TIF_NOTIFY_RESUME)) {
> >> +		__set_current_state(TASK_RUNNING);
> >> +		resume_user_mode_work(NULL);
> >> +	}
> >> +
> >>  	/*
> >>  	 * PF_IO_WORKER never returns to userspace, so check here if we have
> >>  	 * notify work that needs processing.
> >>  	 */
> >>  	if (current->flags & PF_IO_WORKER) {
> >> -		if (test_thread_flag(TIF_NOTIFY_RESUME)) {
> >> -			__set_current_state(TASK_RUNNING);
> >> -			resume_user_mode_work(NULL);
> >> -		}
> >>  		if (current->io_uring) {
> >>  			unsigned int count = 0;
> >>  
> >>
> > 
> > Can confirm that also this patch fixes the issue on my end (both with the
> > reordering of the task_work and without it).
> 
> Great, thanks for testing! Sent out a v2. No need to test it unless you
> absolutely want to ;-)
> 
> > Also found a different way to trigger the issue that does not misuse
> > IOSQE_IO_LINK. Do three sends with IOSQE_CQE_SKIP_SUCCESS | IOSQE_IO_LINK
> > followed by a close with IOSQE_CQE_SKIP_SUCCESS on a ring with
> > IORING_SETUP_DEFER_TASKRUN.
> > 
> > I confirmed that that test case also first brakes on
> > 846072f16eed3b3fb4e59b677f3ed8afb8509b89 and is fixed by either of the
> > two patches you sent.
> > 
> > Not sure if that's a preferable test case compared to the weirder ealier one.
> > You can find it below as a patch to the existing test case in the liburing
> > repo:
> 
> I think that's an improvement, just because it doesn't rely on a weird
> usage of IOSQE_IO_LINK. And it looks good to me - do you want me to
> commit this directly, or do you want to send a "proper" patch (or github
> PR) to retain the proper attribution to you?
> 

Sent the PR with one minor change (adjusted the user data for the third
send).