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

[Stefan Bader]

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
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