memcg/sl[au]b: track all the memcg children of a kmem_cache

This enables us to remove all the children of a kmem_cache being
destroyed, if for example the kernel module it's being used in gets
unloaded.  Otherwise, the children will still point to the destroyed
parent.

Signed-off-by: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Glauber Costa <glommer@parallels.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Frederic Weisbecker <fweisbec@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: JoonSoo Kim <js1304@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 50 insertions, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 270a36789859..4b68ec2c8df6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2772,6 +2772,8 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
         memcg_check_events(memcg, page);
 }
 
+static DEFINE_MUTEX(set_limit_mutex);
+
 #ifdef CONFIG_MEMCG_KMEM
 static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
 {
@@ -3176,6 +3178,51 @@ out:
         return new_cachep;
 }
 
+void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
+{
+        struct kmem_cache *c;
+        int i;
+
+        if (!s->memcg_params)
+                return;
+        if (!s->memcg_params->is_root_cache)
+                return;
+
+        /*
+         * If the cache is being destroyed, we trust that there is no one else
+         * requesting objects from it. Even if there are, the sanity checks in
+         * kmem_cache_destroy should caught this ill-case.
+         *
+         * Still, we don't want anyone else freeing memcg_caches under our
+         * noses, which can happen if a new memcg comes to life. As usual,
+         * we'll take the set_limit_mutex to protect ourselves against this.
+         */
+        mutex_lock(&set_limit_mutex);
+        for (i = 0; i < memcg_limited_groups_array_size; i++) {
+                c = s->memcg_params->memcg_caches[i];
+                if (!c)
+                        continue;
+
+                /*
+                 * We will now manually delete the caches, so to avoid races
+                 * we need to cancel all pending destruction workers and
+                 * proceed with destruction ourselves.
+                 *
+                 * kmem_cache_destroy() will call kmem_cache_shrink internally,
+                 * and that could spawn the workers again: it is likely that
+                 * the cache still have active pages until this very moment.
+                 * This would lead us back to mem_cgroup_destroy_cache.
+                 *
+                 * But that will not execute at all if the "dead" flag is not
+                 * set, so flip it down to guarantee we are in control.
+                 */
+                c->memcg_params->dead = false;
+                cancel_delayed_work_sync(&c->memcg_params->destroy);
+                kmem_cache_destroy(c);
+        }
+        mutex_unlock(&set_limit_mutex);
+}
+
 struct create_work {
         struct mem_cgroup *memcg;
         struct kmem_cache *cachep;
@@ -4284,8 +4331,6 @@ void mem_cgroup_print_bad_page(struct page *page)
 }
 #endif
 
-static DEFINE_MUTEX(set_limit_mutex);
-
 static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                                 unsigned long long val)
 {
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1c424b6511bf..080a43804bf1 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -249,6 +249,9 @@ EXPORT_SYMBOL(kmem_cache_create);
 
 void kmem_cache_destroy(struct kmem_cache *s)
 {
+        /* Destroy all the children caches if we aren't a memcg cache */
+        kmem_cache_destroy_memcg_children(s);
+
         get_online_cpus();
         mutex_lock(&slab_mutex);
         s->refcount--;