selftests/epoll: add a regression test for pipe->poll_usage

pipe->poll_usage was added to ensure that edge-triggered epoll consumers
get a wakeup on every write, even if the pipe was already non-empty.
However, none of the existing epoll_wakeup_test cases cover this; the
test suite passes even with WRITE_ONCE(pipe->poll_usage, true) removed.

Add a test that writes twice to a pipe and verifies that epoll_wait with
EPOLLET reports data each time. This covers the pipe-specific per-write
wakeup behavior that edge-triggered consumers depend on.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://patch.msgid.link/amnlGZesXu-SUK2H@redhat.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions