On 08/06/2016 10:17, Borislav Petkov wrote: >> > - version = __pvclock_read_cycles(src, &ret, &flags); >> > + version = src->version; >> > + /* Make the latest version visible */ >> > + smp_rmb(); >> > + >> > + flags = src->flags; >> > /* Make sure that the version double-check is last. */ > What does that comment mean over the barrier? It should be over the > "while" line IMO. > >> > smp_rmb(); > Why the two barriers back-to-back? Can't have one at the end for all? >
This is basically implementing a seqcount. It needs two barriers and, technically, they should be virt_rmb() -- it really doesn't matter of course because reads are never reordered on x86. Paolo
