On Wed, Jun 05, 2013 at 06:53:45PM -0400, Johannes Weiner wrote: > The lockless reclaim hierarchy iterator currently has a misplaced > barrier that can lead to use-after-free crashes. > > The reclaim hierarchy iterator consist of a sequence count and a > position pointer that are read and written locklessly, with memory > barriers enforcing ordering. > > The write side sets the position pointer first, then updates the > sequence count to "publish" the new position. Likewise, the read side > must read the sequence count first, then the position. If the > sequence count is up to date, it's guaranteed that the position is up > to date as well: > > writer: reader: > iter->position = position if iter->sequence == expected: > smp_wmb() smp_rmb() > iter->sequence = sequence position = iter->position > > However, the read side barrier is currently misplaced, which can lead > to dereferencing stale position pointers that no longer point to valid > memory. Fix this. > > Reported-by: Tejun Heo <tj@xxxxxxxxxx> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: stable@xxxxxxxxxx [3.10+] Reviewed-by: Tejun Heo <tj@xxxxxxxxxx> Oops, right, the references were reversed too. Thanks. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>