[SRU][P][PATCH 0/1] fs/eventpoll: fix endless busy loop after timeout has expired

[Zixing Liu]

BugLink: https://bugs.launchpad.net/linux/+bug/2110289

SRU Justification:

[Impact]

fs/eventpoll: fix endless busy loop after timeout has expired

commit 0a65bc27bd64 introduced a regression where if the epoll time-out
is too small and ep_poll(...) is entered after the time-out already
reached, the kernel will soft-lock itself due to improper time-out handling.

[Fix]

Plucky: cherry-picked from upstream stable linux-6.14.y
Oracular: not affected
Noble:    not affected
Jammy:    not affected
Focal:    not affected
Bionic:   not affected
Xenial:   not affected
Trusty:   not affected

[Test Plan]

* Use the provided reproducer to check if the test program will
cause high CPU usage.
* Check if snapd still causes high CPU usage every 5 minutes.

[Where problems could occur]

The change involves fixing the timed-out handling logic when
the timer expires before the event is processed in the wait queue.
This may cause epoll-related issues if the fix is found to
be inappropriate.

[Notes]

Oracular and below are not affected, as the commit introduced regression
was not present in older kernels or their stable trees.

Max Kellermann (1):
  fs/eventpoll: fix endless busy loop after timeout has expired

 fs/eventpoll.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

-- 
2.48.1