Re: [PATCH] io_uring: prevent eventfd recursion on poll

[Daurnimator <quae@daurnimator.com>]

On Fri, 31 Jan 2020 at 16:25, Jens Axboe <axboe@kernel.dk> wrote:
>
> If we register an eventfd with io_uring for completion notification,
> and then subsequently does a poll for that very descriptor, then we
> can trigger a deadlock scenario. Once a request completes and signals
> the eventfd context, that will in turn trigger the poll command to
> complete. When that poll request completes, it'll try trigger another
> event on the eventfd, but this time off the path led us to complete
> the poll in the first place. The result is a deadlock in eventfd,
> as it tries to ctx->wqh.lock in a nested fashion.
>
> Check if the file in question for the poll request is our eventfd
> context, and if it is, don't trigger a nested event for the poll
> completion.

Could this deadlock/loop also happen via an epoll fd?