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. -- 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/
