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 <[email protected]> > Signed-off-by: Johannes Weiner <[email protected]> > Cc: [email protected] [3.10+]
Reviewed-by: Tejun Heo <[email protected]> Oops, right, the references were reversed too. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
