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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe