Re: [PATCH 4/6] io_uring: let fast poll support multishot

[Hao Xu <haoxu@linux.alibaba.com>]

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@linux.alibaba.com>
>>> ---
>>>   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...
>>
>>> +    }
>>> +
>>>       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))
>>>
>>