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

[Hao Xu]

在 2021/8/9 上午1:31, Nadav Amit 写道:
> > On Aug 8, 2021, at 5:55 AM, Pavel Begunkov <asml.silence@xxxxxxxxx> wrote:
> >
> > On 8/8/21 1:13 AM, Nadav Amit wrote:
> > > From: Nadav Amit <namit@xxxxxxxxxx>
> > >
> > > 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?