1 files changed, 21 insertions, 22 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8fcc86f1d7bc..4375b1e9bd56 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -170,6 +170,20 @@ static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_MEMCG_KMEM
+
+/*
+ * We allow subsystems to populate their shrinker-related
+ * LRU lists before register_shrinker_prepared() is called
+ * for the shrinker, since we don't want to impose
+ * restrictions on their internal registration order.
+ * In this case shrink_slab_memcg() may find corresponding
+ * bit is set in the shrinkers map.
+ *
+ * This value is used by the function to detect registering
+ * shrinkers and to skip do_shrink_slab() calls for them.
+ */
+#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
+
 static DEFINE_IDR(shrinker_idr);
 static int shrinker_nr_max;
 
@@ -179,7 +193,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 
 	down_write(&shrinker_rwsem);
 	/* This may call shrinker, so it must use down_read_trylock() */
-	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+	id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
 	if (id < 0)
 		goto unlock;
 
@@ -364,21 +378,6 @@ int prealloc_shrinker(struct shrinker *shrinker)
 	if (!shrinker->nr_deferred)
 		return -ENOMEM;
 
-	/*
-	 * There is a window between prealloc_shrinker()
-	 * and register_shrinker_prepared(). We don't want
-	 * to clear bit of a shrinker in such the state
-	 * in shrink_slab_memcg(), since this will impose
-	 * restrictions on a code registering a shrinker
-	 * (they would have to guarantee, their LRU lists
-	 * are empty till shrinker is completely registered).
-	 * So, we differ the situation, when 1)a shrinker
-	 * is semi-registered (id is assigned, but it has
-	 * not yet linked to shrinker_list) and 2)shrinker
-	 * is not registered (id is not assigned).
-	 */
-	INIT_LIST_HEAD(&shrinker->list);
-
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
 		if (prealloc_memcg_shrinker(shrinker))
 			goto free_deferred;
@@ -408,6 +407,9 @@ void register_shrinker_prepared(struct shrinker *shrinker)
 {
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
+#ifdef CONFIG_MEMCG_KMEM
+	idr_replace(&shrinker_idr, shrinker, shrinker->id);
+#endif
 	up_write(&shrinker_rwsem);
 }
 
@@ -589,15 +591,12 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 		struct shrinker *shrinker;
 
 		shrinker = idr_find(&shrinker_idr, i);
-		if (unlikely(!shrinker)) {
-			clear_bit(i, map->map);
+		if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
+			if (!shrinker)
+				clear_bit(i, map->map);
 			continue;
 		}
 
-		/* See comment in prealloc_shrinker() */
-		if (unlikely(list_empty(&shrinker->list)))
-			continue;
-
 		ret = do_shrink_slab(&sc, shrinker, priority);
 		if (ret == SHRINK_EMPTY) {
 			clear_bit(i, map->map);