From ba88acf8c2fa50c8318ad9ea6e757a291d94e70e Mon Sep 17 00:00:00 2001 From: Martijn Coenen Date: Thu, 14 Jan 2016 14:33:52 +0100 Subject: [PATCH] UPSTREAM: memcg: Only free spare array when readers are done A spare array holding mem cgroup threshold events is kept around to make sure we can always safely deregister an event and have an array to store the new set of events in. In the scenario where we're going from 1 to 0 registered events, the pointer to the primary array containing 1 event is copied to the spare slot, and then the spare slot is freed because no events are left. However, it is freed before calling synchronize_rcu(), which means readers may still be accessing threshold->primary after it is freed. Fixed by only freeing after synchronize_rcu(). Change-Id: Iee3ad8eb400612ec24898832eb19ff34eb2aecb4 Signed-off-by: Martijn Coenen --- mm/memcontrol.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ec0989684367..a19c72138334 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5790,16 +5790,17 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp, swap_buffers: /* Swap primary and spare array */ thresholds->spare = thresholds->primary; - /* If all events are unregistered, free the spare array */ - if (!new) { - kfree(thresholds->spare); - thresholds->spare = NULL; - } rcu_assign_pointer(thresholds->primary, new); /* To be sure that nobody uses thresholds */ synchronize_rcu(); + + /* If all events are unregistered, free the spare array */ + if (!new) { + kfree(thresholds->spare); + thresholds->spare = NULL; + } unlock: mutex_unlock(&memcg->thresholds_lock); }