On Tue, 14 Apr 2015 19:12:33 -0700 Jason Low <jason.l...@hp.com> wrote:
> Hi Steven, > > On Tue, 2015-04-14 at 19:59 -0400, Steven Rostedt wrote: > > On Tue, 14 Apr 2015 16:09:44 -0700 > > Jason Low <jason.l...@hp.com> wrote: > > > > > > > @@ -2088,7 +2088,7 @@ void task_numa_fault(int last_cpupid, int mem_node, > > > int pages, int flags) > > > > > > static void reset_ptenuma_scan(struct task_struct *p) > > > { > > > - ACCESS_ONCE(p->mm->numa_scan_seq)++; > > > + WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1); > > > > Is the READ_ONCE() inside the WRITE_ONCE() really necessary? > > Yeah, I think so to be safe, otherwise, the access of > p->mm->numa_scan_seq in the 2nd parameter doesn't have the volatile > cast. You are correct. Now I'm thinking that the WRITE_ONCE() is not needed, and just a: p->mm->numa_scan_seq = READ_ONCE(p->numa_scan_seq) + 1; Can be done. But I'm still trying to wrap my head around why this is needed here. Comments would have been really helpful. We should make all READ_ONCE() WRITE_ONCE and obsolete ACCESS_ONCE() have mandatory comments just like we do with memory barriers. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/