On Thu, Aug 30, 2012 at 11:56:25AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul.mcken...@linaro.org> > > The first memory barrier in __call_rcu() is supposed to order any > updates done beforehand by the caller against the actual queuing > of the callback. However, the second memory barrier (which is intended > to order incrementing the queue lengths before queuing the callback) > is also between the caller's updates and the queuing of the callback. > The second memory barrier can therefore serve both purposes. > > This commit therefore removes the first memory barrier.
I don't see any such second memory barrier in __call_rcu(), at least not in current master. Right after this smp_mb(), __call_rcu() enqueues the callback and increments the queue length. Did you add a second memory barrier in some other patch that hasn't made it upstream yet? If so, could you note that patch dependency explicitly in the commit message? - Josh Triplett > Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > --- > kernel/rcutree.c | 2 -- > 1 files changed, 0 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index e58097b..5b6709b 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1923,8 +1923,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct > rcu_head *rcu), > head->func = func; > head->next = NULL; > > - smp_mb(); /* Ensure RCU update seen before callback registry. */ > - > /* > * Opportunistically note grace-period endings and beginnings. > * Note that we might see a beginning right after we see an > -- > 1.7.8 > -- 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/
