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

[Massimiliano Pellizzer]

On Wed, 21 May 2025 at 10:01, Stefan Bader <stefan.bader at canonical.com> wrote:
>
> On 21.05.25 08:21, Zixing Liu wrote:
> > BugLink: https://bugs.launchpad.net/linux/+bug/2110289
>
> We normally use "https://bugs.launchpad.net/bugs/2110289". Also the
> patch looks a little odd at least in TB (having From: twice). And it
> misses the "(cherry picked)" line and the s-o-b. But given the critical
> timing I would fix this all up when applying.
>
> I will wait on feedback from tester before applying but to speed up the
> process already
>
> Acked-by: Stefan Bader <stefan.bader at canonical.com>
>
> >
> > 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(-)
> >
>
>
> --
> - Stefan
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

Except for the formatting issues mentioned by the other reviewer, the
content of the patch looks good to me.

Acked-by: Massimiliano Pellizzer <massimiliano.pellizzer at canonical.com>

-- 
Massimiliano Pellizzer