On Wed, 11 Jul 2007 18:00:58 -0700 "Paul E. McKenney" <[EMAIL PROTECTED]> wrote:
> Turns out that compiler writers are a bit more aggressive about optimizing > than one might expect. This patch prevents a number of such optimizations > from messing up rcu_deference(). This is not merely a theoretical > problem, as evidenced by the rmb() in mce_log(). > > Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]> > --- > > rcupdate.h | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff -urpNa -X dontdiff linux-2.6.22/include/linux/rcupdate.h > linux-2.6.22-volrcud/include/linux/rcupdate.h > --- linux-2.6.22/include/linux/rcupdate.h 2007-07-08 16:32:17.000000000 > -0700 > +++ linux-2.6.22-volrcud/include/linux/rcupdate.h 2007-07-11 > 17:21:09.000000000 -0700 > @@ -217,6 +217,18 @@ extern int rcu_needs_cpu(int cpu); > local_bh_enable(); \ > } while(0) > > +/* > + * Prevent the compiler from merging or refetching accesses. The compiler > + * is also forbidden from reordering successive instances of ACCESS_ONCE(), > + * but only when the compiler is aware of some particular ordering. One way > + * to make the compiler aware of ordering is to put the two invocations of > + * ACCESS_ONCE() in different C statements. > + * > + * This macro does absolutely -nothing- to prevent the CPU from reordering, > + * merging, or refetching absolutely anything at any time. > + */ > +#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) drivers/net/hamradio/bpqether.c: In function 'bpq_seq_next': drivers/net/hamradio/bpqether.c:421: error: invalid lvalue in unary '&' - 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/
