tree ef6390b2e72c706503b7197422d6ab293498b1b3
parent 3eb409b63f6c8369509bedea8d045be8e7aa5ded
author Martijn Coenen <maco@google.com> 1452778432 +0100
committer Martijn Coenen <maco@google.com> 1453229311 +0000

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 <maco@google.com>