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

[Jens Axboe <axboe@kernel.dk>]

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?

-- 
Jens Axboe