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...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Johannes Weiner hannes@cmpxchg.org 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@cmpxchg.org Fixes: 45190f01dd40 ("mm/zswap.c: add allocation hysteresis if pool limit is hit") Signed-off-by: Johannes Weiner hannes@cmpxchg.org Reported-by: Chris Mason clm@fb.com Cc: Vitaly Wool vitaly.wool@konsulko.com Cc: Domenico Cerasuolo cerasuolodomenico@gmail.com Cc: Nhat Pham nphamcs@gmail.com Cc: stable@vger.kernel.org [5.6+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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; }

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Patches currently in -mm which might be from hannes@cmpxchg.org are

mm-zswap-fix-pool-refcount-bug-around-shrink_worker.patch