Re: [PATCH] memcg: Only free spare array when readers are done

[Johannes Weiner]

On Thu, Jan 14, 2016 at 02:33:52PM +0100, Martijn Coenen wrote:
> 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().
> 
> Signed-off-by: Martijn Coenen <maco@xxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>