The patch titled
Subject: mm: zswap: fix pool refcount bug around shrink_worker()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-zswap-fix-pool-refcount-bug-around-shrink_worker.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-fix-pool-refcount-bug-around-shrink_worker.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: zswap: fix pool refcount bug around shrink_worker()
Date: Fri, 6 Oct 2023 12:00:24 -0400
When a zswap store fails due to the limit, it acquires a pool reference
and queues the shrinker. When the shrinker runs, it drops the reference.
However, there can be multiple store attempts before the shrinker wakes up
and runs once. This results in reference leaks and eventual saturation
warnings for the pool refcount.
Fix this by dropping the reference again when the shrinker is already
queued. This ensures one reference per shrinker run.
Link: https://lkml.kernel.org/r/20231006160024.170748-1-hannes@xxxxxxxxxxx
Fixes: 45190f01dd40 ("mm/zswap.c: add allocation hysteresis if pool limit is hit")
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reported-by: Chris Mason <clm@xxxxxx>
Cc: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.6+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/zswap.c~mm-zswap-fix-pool-refcount-bug-around-shrink_worker
+++ a/mm/zswap.c
@@ -1383,8 +1383,8 @@ reject:
shrink:
pool = zswap_pool_last_get();
- if (pool)
- queue_work(shrink_wq, &pool->shrink_work);
+ if (pool && !queue_work(shrink_wq, &pool->shrink_work))
+ zswap_pool_put(pool);
goto reject;
}
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
mm-zswap-fix-pool-refcount-bug-around-shrink_worker.patch
