[PATCH v2] mm/shrinker: Fix refcount leak in shrink_slab_memcg()

[Altan Hacigumus]

When kmem is disabled for memcg, slab-backed shrinkers are skipped.
However, shrink_slab_memcg() doesn't drop the reference acquired via
shrinker_try_get() before continuing.

Add the missing shrinker_put().

Also, since memcg_kmem_online() and shrinker flags cannot change
dynamically, remove the shrinker from the bitmap to avoid unnecessary
future scans.

Fixes: 50d09da8e119 ("mm: shrinker: make memcg slab shrink lockless")
Suggested-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Acked-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20260203073757.135088-1-ahacigu.linux@xxxxxxxxx
Signed-off-by: Altan Hacigumus <ahacigu.linux@xxxxxxxxx>
---
Changes in v2:
- Use clear_bit() to remove shrinker from bitmap instead of just skipping
---
 mm/shrinker.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/shrinker.c b/mm/shrinker.c
index 4a93fd433689..68dc7b4242f2 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -544,8 +544,11 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 
 			/* Call non-slab shrinkers even though kmem is disabled */
 			if (!memcg_kmem_online() &&
-			    !(shrinker->flags & SHRINKER_NONSLAB))
+			    !(shrinker->flags & SHRINKER_NONSLAB)) {
+				clear_bit(offset, unit->map);
+				shrinker_put(shrinker);
 				continue;
+			}
 
 			ret = do_shrink_slab(&sc, shrinker, priority);
 			if (ret == SHRINK_EMPTY) {
-- 
2.43.0