Re: [PATCH] io_uring: simplify the SQPOLL thread check when cancelling requests

Bui Quang Minh
2025-01-13T15:33:23Z

On 1/13/25 04:15, Pavel Begunkov wrote:
> On 1/12/25 16:14, Bui Quang Minh wrote:
> ...
>>>> @@ -2898,7 +2899,12 @@ static __cold void io_ring_exit_work(struct
>>>> work_struct *work)
>>>>           if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
>>>>               io_move_task_work_from_local(ctx);
>>>>
>>>> -        while (io_uring_try_cancel_requests(ctx, NULL, true))
>>>> +        /*
>>>> +         * Even if SQPOLL thread reaches this path, don't force
>>>> +         * iopoll here, let the io_uring_cancel_generic handle
>>>> +         * it.
>>>
>>> Just curious, will sq_thread enter this io_ring_exit_work path?
>>
>> AFAIK, yes. The SQPOLL thread is created with create_io_thread, this
>> function creates a new task with CLONE_FILES. So all the open files is
>> shared. There will be case that the parent closes its io_uring file
>> and SQPOLL thread become the only owner of that file. So it can reach
>> this path when terminating.
>
> The function is run by a separate kthread, the sqpoll task doesn't
> call it directly.

Yeah, the io_uring_release can be called in sqpoll thread but the
io_ring_exit_work is queued in the io_uring workqueue so that function
is executed in a kthread worker.

I will update the comment and commit message.

Thanks,
Quang Minh.