Re: [PATCH 1/2] io_uring: clear TIF_NOTIFY_SIGNAL when running task work

Hao Xu
2021-08-09T04:07:48Z

在 2021/8/9 上午1:31, Nadav Amit 写道:
>
>
>> On Aug 8, 2021, at 5:55 AM, Pavel Begunkov <asml.silence@gmail.com> wrote:
>>
>> On 8/8/21 1:13 AM, Nadav Amit wrote:
>>> From: Nadav Amit <namit@vmware.com>
>>>
>>> When using SQPOLL, the submission queue polling thread calls
>>> task_work_run() to run queued work. However, when work is added with
>>> TWA_SIGNAL - as done by io_uring itself - the TIF_NOTIFY_SIGNAL remains
>>
>> static int io_req_task_work_add(struct io_kiocb *req)
>> {
>> ...
>> notify = (req->ctx->flags & IORING_SETUP_SQPOLL) ? TWA_NONE : TWA_SIGNAL;
>> if (!task_work_add(tsk, &tctx->task_work, notify))
>> ...
>> }
>>
>> io_uring doesn't set TIF_NOTIFY_SIGNAL for SQPOLL. But if you see it, I'm
>> rather curious who does.
>
> I was saying io-uring, but I meant io-uring in the wider sense:
> io_queue_worker_create().
>
> Here is a call trace for when TWA_SIGNAL is used. io_queue_worker_create()
> uses TWA_SIGNAL. It is called by io_wqe_dec_running(), and not shown due
> to inlining:
Hi Nadav, Pavel,
How about trying to make this kind of call to use TWA_NONE for sqthread,
though I know for this case currently there is no info to get to know if
task is sqthread. I think we shouldn't kick sqthread.

regards,
Hao
>
> [ 70.540761] Call Trace:
> [ 70.541352] dump_stack+0x7d/0x9c
> [ 70.541930] task_work_add.cold+0x9/0x12
> [ 70.542591] io_wqe_dec_running+0xd6/0xf0
> [ 70.543259] io_wq_worker_sleeping+0x3d/0x60
> [ 70.544106] schedule+0xa0/0xc0
> [ 70.544673] userfaultfd_read_iter+0x2c3/0x790
> [ 70.545374] ? wake_up_q+0xa0/0xa0
> [ 70.545887] io_iter_do_read+0x1e/0x40
> [ 70.546531] io_read+0xdc/0x340
> [ 70.547148] ? update_curr+0x72/0x1c0
> [ 70.547887] ? update_load_avg+0x7c/0x600
> [ 70.548538] ? __switch_to_xtra+0x10a/0x500
> [ 70.549264] io_issue_sqe+0xd99/0x1840
> [ 70.549887] ? lock_timer_base+0x72/0xa0
> [ 70.550516] ? try_to_del_timer_sync+0x54/0x80
> [ 70.551224] io_wq_submit_work+0x87/0xb0
> [ 70.552001] io_worker_handle_work+0x2b5/0x4b0
> [ 70.552705] io_wqe_worker+0xd6/0x2f0
> [ 70.553364] ? recalc_sigpending+0x1c/0x50
> [ 70.554074] ? io_worker_handle_work+0x4b0/0x4b0
> [ 70.554813] ret_from_fork+0x22/0x30
>
> Does it answer your question?
>