[SRU Focal/Groovy] UBUNTU: SAUCE: Revert "mm: memcg/slab: fix memory leak at non-root kmem_cache destroy"

[Thadeu Lima de Souza Cascardo]

BugLink: https://bugs.launchpad.net/bugs/1894780

This reverts commit 79ffe7107b13042c69c4a06394175362121b06b5. This is
commit d38a2b7a9c939e6d7329ab92b96559ccebf7b135 upstream.

Said commit causes same-sized kmemcaches to become unmergeable, and when a
new kmemcache is created, it will fail creating the sysfs entry, making the
kmemcache creation to fail.

Considering the original commit fix a leak but causes a different leak and
failures to create kmemcaches, the revert is preferable until a proper fix
is developed.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 mm/slab_common.c | 35 +++++++----------------------------
 1 file changed, 7 insertions(+), 28 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index e36dd36c7076..8c1ffbf7de45 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -326,14 +326,6 @@ int slab_unmergeable(struct kmem_cache *s)
 	if (s->refcount < 0)
 		return 1;
 
-#ifdef CONFIG_MEMCG_KMEM
-	/*
-	 * Skip the dying kmem_cache.
-	 */
-	if (s->memcg_params.dying)
-		return 1;
-#endif
-
 	return 0;
 }
 
@@ -894,15 +886,12 @@ static int shutdown_memcg_caches(struct kmem_cache *s)
 	return 0;
 }
 
-static void memcg_set_kmem_cache_dying(struct kmem_cache *s)
+static void flush_memcg_workqueue(struct kmem_cache *s)
 {
 	spin_lock_irq(&memcg_kmem_wq_lock);
 	s->memcg_params.dying = true;
 	spin_unlock_irq(&memcg_kmem_wq_lock);
-}
 
-static void flush_memcg_workqueue(struct kmem_cache *s)
-{
 	/*
 	 * SLAB and SLUB deactivate the kmem_caches through call_rcu. Make
 	 * sure all registered rcu callbacks have been invoked.
@@ -934,6 +923,10 @@ static inline int shutdown_memcg_caches(struct kmem_cache *s)
 {
 	return 0;
 }
+
+static inline void flush_memcg_workqueue(struct kmem_cache *s)
+{
+}
 #endif /* CONFIG_MEMCG_KMEM */
 
 void slab_kmem_cache_release(struct kmem_cache *s)
@@ -951,6 +944,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
 	if (unlikely(!s))
 		return;
 
+	flush_memcg_workqueue(s);
+
 	get_online_cpus();
 	get_online_mems();
 
@@ -960,22 +955,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
 	if (s->refcount)
 		goto out_unlock;
 
-#ifdef CONFIG_MEMCG_KMEM
-	memcg_set_kmem_cache_dying(s);
-
-	mutex_unlock(&slab_mutex);
-
-	put_online_mems();
-	put_online_cpus();
-
-	flush_memcg_workqueue(s);
-
-	get_online_cpus();
-	get_online_mems();
-
-	mutex_lock(&slab_mutex);
-#endif
-
 	err = shutdown_memcg_caches(s);
 	if (!err)
 		err = shutdown_cache(s);
-- 
2.25.1