The commit is pushed to "branch-rh7-3.10.0-1127.vz7.150.x-ovz" and will appear
at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.vz7.150.8
------>
commit cd3eaf13e6373f690b75dd17a0bed42521475b46
Author: Kirill Tkhai <[email protected]>
Date: Thu May 7 21:30:07 2020 +0300
mm: Add RCU read brackets into memcg_uncharge_kmem()
Potentially, here can be last css refcnt, so we should
have stable memory to access parent pointer.
Signed-off-by: Kirill Tkhai <[email protected]>
---
mm/memcontrol.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 797cb8e6df6d7..e82c59f6a9840 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3525,7 +3525,13 @@ void memcg_uncharge_kmem(struct mem_cgroup *memcg,
*
* The memory barrier imposed by test&clear is paired with the
* explicit one in memcg_kmem_mark_dead().
+ *
+ * We take RCU to remain memcg memory stable for parent dereferencing.
+ * Parent's memory is stable even in case of page_counter_uncharge()
+ * has decremented its last charged memory, because child dentry owns
+ * parents's dentry refcnt.
*/
+ rcu_read_lock();
if (memcg_kmem_test_and_clear_dead(memcg))
css_put(&memcg->css);
@@ -3541,6 +3547,7 @@ void memcg_uncharge_kmem(struct mem_cgroup *memcg,
else
break;
}
+ rcu_read_unlock();
}
int __memcg_charge_slab(struct kmem_cache *s, gfp_t gfp, unsigned int nr_pages)
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