memcg: don't need to free memcg via RCU or workqueue

Now memcg has the same life cycle with its corresponding cgroup, and a
cgroup is freed via RCU and then mem_cgroup_css_free() will be called in
a work function, so we can simply call __mem_cgroup_free() in
mem_cgroup_css_free().

This actually reverts commit 59927fb984d ("memcg: free mem_cgroup by RCU
to fix oops").

Signed-off-by: Li Zefan <lizefan@huawei.com>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Glauber Costa <glommer@openvz.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 46 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fa521a2f4bf6..d12ca6f3c293 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -263,28 +263,10 @@ struct mem_cgroup {
         /* vmpressure notifications */
         struct vmpressure vmpressure;
 
-        union {
-                /*
-                 * the counter to account for mem+swap usage.
-                 */
-                struct res_counter memsw;
-
-                /*
-                 * rcu_freeing is used only when freeing struct mem_cgroup,
-                 * so put it into a union to avoid wasting more memory.
-                 * It must be disjoint from the css field.  It could be
-                 * in a union with the res field, but res plays a much
-                 * larger part in mem_cgroup life than memsw, and might
-                 * be of interest, even at time of free, when debugging.
-                 * So share rcu_head with the less interesting memsw.
-                 */
-                struct rcu_head rcu_freeing;
-                /*
-                 * We also need some space for a worker in deferred freeing.
-                 * By the time we call it, rcu_freeing is no longer in use.
-                 */
-                struct work_struct work_freeing;
-        };
+        /*
+         * the counter to account for mem+swap usage.
+         */
+        struct res_counter memsw;
 
         /*
          * the counter to account for kernel memory usage.
@@ -6211,29 +6193,6 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
                 vfree(memcg);
 }
 
-
-/*
- * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
- * but in process context.  The work_freeing structure is overlaid
- * on the rcu_freeing structure, which itself is overlaid on memsw.
- */
-static void free_work(struct work_struct *work)
-{
-        struct mem_cgroup *memcg;
-
-        memcg = container_of(work, struct mem_cgroup, work_freeing);
-        __mem_cgroup_free(memcg);
-}
-
-static void free_rcu(struct rcu_head *rcu_head)
-{
-        struct mem_cgroup *memcg;
-
-        memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
-        INIT_WORK(&memcg->work_freeing, free_work);
-        schedule_work(&memcg->work_freeing);
-}
-
 /*
  * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
  */
@@ -6383,7 +6342,7 @@ static void mem_cgroup_css_free(struct cgroup *cont)
         struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
 
         memcg_destroy_kmem(memcg);
-        call_rcu(&memcg->rcu_freeing, free_rcu);
+        __mem_cgroup_free(memcg);
 }
 
 #ifdef CONFIG_MMU