From: Joel Fernandes (Google) Date: Wed, 14 Oct 2020 22:21:53 +0000 (-0400) Subject: rcu/tree: segcblist: Remove redundant smp_mb()s X-Git-Tag: howlett/maple/20220722_2~3773^2~1^2^5~23 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=68804cf1c905ce227e4e1d0bc252c216811c59fd;p=users%2Fjedix%2Flinux-maple.git rcu/tree: segcblist: Remove redundant smp_mb()s The full memory barriers in rcu_segcblist_enqueue() and in rcu_do_batch() are not needed because rcu_segcblist_add_len(), and thus also rcu_segcblist_inc_len(), already includes a memory barrier *before* and *after* the length of the list is updated. This commit therefore removes these redundant smp_mb() invocations. Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c index 777780447887..1e80a0a9036a 100644 --- a/kernel/rcu/rcu_segcblist.c +++ b/kernel/rcu/rcu_segcblist.c @@ -327,7 +327,6 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp, struct rcu_head *rhp) { rcu_segcblist_inc_len(rsclp); - smp_mb(); /* Ensure counts are updated before callback is enqueued. */ rcu_segcblist_inc_seglen(rsclp, RCU_NEXT_TAIL); rhp->next = NULL; WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cc6f379c7ddf..b0fb654cba80 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2523,7 +2523,6 @@ static void rcu_do_batch(struct rcu_data *rdp) /* Update counts and requeue any remaining callbacks. */ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl); - smp_mb(); /* List handling before counting for rcu_barrier(). */ rcu_segcblist_add_len(&rdp->cblist, -count); /* Reinstate batch limit if we have worked down the excess. */