On 9/8/21 12:21 PM, Hao Xu wrote:
> 在 2021/9/7 下午2:48, Hao Xu 写道:
>> 在 2021/9/7 上午3:04, Pavel Begunkov 写道:
>>> On 9/3/21 12:00 PM, Hao Xu wrote:
>>>> For operations like accept, multishot is a useful feature, since we can
>>>> reduce a number of accept sqe. Let's integrate it to fast poll, it may
>>>> be good for other operations in the future.
>>>>
>>>> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
>>>> ---
>>>> fs/io_uring.c | 15 ++++++++++++---
>>>> 1 file changed, 12 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>> index d6df60c4cdb9..dae7044e0c24 100644
>>>> --- a/fs/io_uring.c
>>>> +++ b/fs/io_uring.c
>>>> @@ -5277,8 +5277,15 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
>>>> return;
>>>> }
>>>> - hash_del(&req->hash_node);
>>>> - io_poll_remove_double(req);
>>>> + if (READ_ONCE(apoll->poll.canceled))
>>>> + apoll->poll.events |= EPOLLONESHOT;
>>>> + if (apoll->poll.events & EPOLLONESHOT) {
>>>> + hash_del(&req->hash_node);
>>>> + io_poll_remove_double(req);
>>>> + } else {
>>>> + add_wait_queue(apoll->poll.head, &apoll->poll.wait);
>>>
>>> It looks like it does both io_req_task_submit() and adding back
>>> to the wq, so io_issue_sqe() may be called in parallel with
>>> io_async_task_func(). If so, there will be tons of all kind of
>>> races.
>> IMHO, io_async_task_func() is called in original context one by
>> one(except PF_EXITING is set, it is also called in system-wq), so
>> shouldn't be parallel case there.
> ping...
fwiw, the case we're talking about:
CPU0 | CPU1
io_async_task_func() |
-> add_wait_queue(); |
-> io_req_task_submit(); |
/* no tw run happened in between */
| io_async_task_func()
| --> io_req_task_submit()
We called io_req_task_submit() twice without running tw in-between,
both of the calls use the same req->io_task_work.node field in the
request for accounting, and so the second call will screw
tctx->task_list and not only by not considering that
req->io_task_work.node is already taken/enqueued.
io_req_task_work_add() {
wq_list_add_tail(&req->io_task_work.node, &tctx->task_list);
}
>>>
>>>> + }
>>>> +
>>>> spin_unlock(&ctx->completion_lock);
>>>> if (!READ_ONCE(apoll->poll.canceled))
>>>> @@ -5366,7 +5373,7 @@ static int io_arm_poll_handler(struct io_kiocb *req)
>>>> struct io_ring_ctx *ctx = req->ctx;
>>>> struct async_poll *apoll;
>>>> struct io_poll_table ipt;
>>>> - __poll_t ret, mask = EPOLLONESHOT | POLLERR | POLLPRI;
>>>> + __poll_t ret, mask = POLLERR | POLLPRI;
>>>> int rw;
>>>> if (!req->file || !file_can_poll(req->file))
>>>> @@ -5388,6 +5395,8 @@ static int io_arm_poll_handler(struct io_kiocb *req)
>>>> rw = WRITE;
>>>> mask |= POLLOUT | POLLWRNORM;
>>>> }
>>>> + if (!(req->flags & REQ_F_APOLL_MULTISHOT))
>>>> + mask |= EPOLLONESHOT;
>>>> /* if we can't nonblock try, then no point in arming a poll handler */
>>>> if (!io_file_supports_nowait(req, rw))
>>>>
>>>
>
--
Pavel Begunkov
