mm/shrinker: fix refcount leak in shrink_slab_memcg()

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.

Link: https://lkml.kernel.org/r/20260204033553.50039-1-ahacigu.linux@gmail.com
Fixes: 50d09da8e119 ("mm: shrinker: make memcg slab shrink lockless")
Signed-off-by: Altan Hacigumus <ahacigu.linux@gmail.com>
Acked-by: Qi Zheng <zhengqi.arch@bytedance.com>
Link: https://lore.kernel.org/r/20260203073757.135088-1-ahacigu.linux@gmail.com
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/shrinker.c b/mm/shrinker.c
index 7b61fc0ee78fb0a37c183f73fd00b8b0d0f539e7..94646ee0af63bc4afddc458e658b1455743c2040 100644 (file)
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -544,8 +544,11 @@ again:
 
                        /* 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) {