We can have dependencies between epoll and io_uring. Consider an epoll context, identified by the epfd file descriptor, and an io_uring file descriptor identified by iofd. If we add iofd to the epfd context, and arm a multishot poll request for epfd with iofd, then the multishot poll request will repeatedly trigger and generate events until terminated by CQ ring overflow. This isn't a desired behavior.

Add EPOLL_URING so that io_uring can pass it in as part of the poll wakeup key, and io_uring can check for that to detect a potential recursive invocation.

Cc: stable@vger.kernel.org # 6.0 Signed-off-by: Jens Axboe axboe@kernel.dk --- fs/eventpoll.c | 18 ++++++++++-------- include/uapi/linux/eventpoll.h | 6 ++++++ 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 52954d4637b5..e864256001e8 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -491,7 +491,8 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi) */ #ifdef CONFIG_DEBUG_LOCK_ALLOC

-static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi) +static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, + unsigned pollflags) { struct eventpoll *ep_src; unsigned long flags; @@ -522,16 +523,17 @@ static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi) } spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests); ep->nests = nests + 1; - wake_up_locked_poll(&ep->poll_wait, EPOLLIN); + wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags); ep->nests = 0; spin_unlock_irqrestore(&ep->poll_wait.lock, flags); }

#else

-static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi) +static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, + unsigned pollflags) { - wake_up_poll(&ep->poll_wait, EPOLLIN); + wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags); }

#endif @@ -742,7 +744,7 @@ static void ep_free(struct eventpoll *ep)

/* We need to release all tasks waiting for these file */ if (waitqueue_active(&ep->poll_wait)) - ep_poll_safewake(ep, NULL); + ep_poll_safewake(ep, NULL, 0);

/* * We need to lock this because we could be hit by @@ -1208,7 +1210,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v

/* We have to call this outside the lock */ if (pwake) - ep_poll_safewake(ep, epi); + ep_poll_safewake(ep, epi, pollflags & EPOLL_URING);

if (!(epi->event.events & EPOLLEXCLUSIVE)) ewake = 1; @@ -1553,7 +1555,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,

/* We have to call this outside the lock */ if (pwake) - ep_poll_safewake(ep, NULL); + ep_poll_safewake(ep, NULL, 0);

return 0; } @@ -1629,7 +1631,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,

/* We have to call this outside the lock */ if (pwake) - ep_poll_safewake(ep, NULL); + ep_poll_safewake(ep, NULL, 0);

return 0; } diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h index 8a3432d0f0dc..532cc7fa75c0 100644 --- a/include/uapi/linux/eventpoll.h +++ b/include/uapi/linux/eventpoll.h @@ -41,6 +41,12 @@ #define EPOLLMSG (__force __poll_t)0x00000400 #define EPOLLRDHUP (__force __poll_t)0x00002000

+/* + * Internal flag - wakeup generated by io_uring, used to detect recursion back + * into the io_uring poll handler. + */ +#define EPOLL_URING ((__force __poll_t)(1U << 27)) + /* Set exclusive wakeup mode for the target file descriptor */ #define EPOLLEXCLUSIVE ((__force __poll_t)(1U << 28))