On Tue, 8 Jul 2014, Christoph Hellwig wrote: > > + if (unlikely(err)) > > + ACCESS_ONCE(bb->error) = err; > > I can't see a reason for the ACCESS_ONCE here. Multiple bios can be completed concurrently, so they write bb->error at the same time. The compiler may do store tearing (see "store tearing" in Documentation/memory-barriers.txt) - it may split one 4-byte write into several smaller writes - and it could result in setting bb->error to invalid value. We need ACCESS_ONCE to make sure that store tearing doesn't happen. Mikulas > Also the likely/unlikely annotations here smell like premature > optimization. > > Otherwise looks good to me. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
