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mm: zswap: fix pool refcount bug around shrink_worker()

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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: 45190f01dd ("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>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: <stable@vger.kernel.org>	[5.6+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2023-10-06 12:00:24 -04:00 committed by Andrew Morton
parent 229e225376
commit 969d63e1af
1 changed files with 2 additions and 2 deletions
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4
mm/zswap.c
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@ -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;
}