Merge patch series "eventpoll: Fix epoll_wait() report false negative"

Nam Cao <namcao@linutronix.de> says:

While staring at epoll, I noticed ep_events_available() looks wrong. I
wrote a small program to confirm, and yes it is definitely wrong.

This series adds a reproducer to kselftest, and fix the bug.

* patches from https://patch.msgid.link/cover.1780422137.git.namcao@linutronix.de:
  eventpoll: Fix epoll_wait() report false negative
  selftests/eventpoll: Add test for multiple waiters

Link: https://patch.msgid.link/cover.1780422137.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <brauner@kernel.org>