On Wed, Nov 06, 2013 at 03:00:11PM +0100, Peter Zijlstra wrote: > On Wed, Nov 06, 2013 at 08:50:47AM -0500, Vince Weaver wrote: > > On Wed, 6 Nov 2013, tip-bot for Peter Zijlstra wrote: > > > > > +++ b/tools/perf/util/evlist.h > > > @@ -177,7 +177,7 @@ int perf_evlist__strerror_open(struct perf_evlist *evlist, int err, char *buf, s > > > static inline unsigned int perf_mmap__read_head(struct perf_mmap *mm) > > > { > > > struct perf_event_mmap_page *pc = mm->base; > > > - int head = pc->data_head; > > > + int head = ACCESS_ONCE(pc->data_head); > > > rmb(); > > > return head; > > > > so is this ACCESS_ONCE required now for proper access to the mmap buffer? > > Pretty much; otherwise your C compiler is allowed to mess it up. > > > remember that there are users trying to use this outside of the kernel > > where we don't necessarily have access to internal kernl macros. Some of > > these users aren't necessarily GPLv2 compatible either (PAPI for example > > is more or less BSD licensed) so just cutting and pasting chunks of > > internal kernel macros isn't always the best route either. > > Other license stuff is not my problem; that said I doubt there's much > copyright to claim on a volatile cast. Also, does PAPI actually use the buffer then? I thought that was strictly self monitoring. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html