On Fri, May 06, 2011 at 09:08:34AM +0200, Andi Kleen wrote:
> > @@ -168,8 +168,13 @@ int __read_mostly timekeeping_suspended;
> > static struct timespec xtime_cache __attribute__ ((aligned (16)));
> > void update_xtime_cache(u64 nsec)
> > {
> > - xtime_cache = xtime;
> > - timespec_add_ns(&xtime_cache, nsec);
> > + /*
> > + * Use temporary variable so get_seconds() cannot catch
> > + * an intermediate xtime_cache.tv_sec value.
> > + */
> > + struct timespec ts = xtime;
> > + timespec_add_ns(&ts, nsec);
>
> There's nothing to stop the compiler's optimizer to use memory accesses
> directly again. Something similar to ACCESS_ONCE (that is essentially a
> volatile cast) may be required to be fully future proof.
I agree, this doesn't look like a viable solution at all.
sorry,
greg k-h
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