Re: [PATCH] io_uring: fix possible deadlock in io_uring_poll

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

在 2021/2/5 上午12:48, Pavel Begunkov 写道:
> On 03/02/2021 01:48, Jens Axboe wrote:
>> On 2/2/21 5:04 PM, Pavel Begunkov wrote:
>>> On 02/02/2021 19:52, Hao Xu wrote:
>>>> This might happen if we do epoll_wait on a uring fd while reading/writing
>>>> the former epoll fd in a sqe in the former uring instance.
>>>> So let's don't flush cqring overflow list when we fail to get the uring
>>>> lock. This leads to less accuracy, but is still ok.
>>>
>>> if (io_cqring_events(ctx) || test_bit(0, &ctx->cq_check_overflow))
>>>          mask |= EPOLLIN | EPOLLRDNORM;
>>>
>>> Instead of flushing. It'd make sense if we define poll as "there might
>>> be something, go do your peek/wait with overflow checks". Jens, is that
>>> documented anywhere?
>>
>> Nope - I actually think that the approach chosen here is pretty good,
>> it'll force the app to actually check and hence do what it needs to do.
> 
> Ok, seems we agree on that.
> 
> Hao, can you send an updated patch?
> 
Sure, will send v2 soon.