From 68804cf1c905ce227e4e1d0bc252c216811c59fd Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Wed, 14 Oct 2020 18:21:53 -0400 Subject: [PATCH] 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 --- kernel/rcu/rcu_segcblist.c | 1 - kernel/rcu/tree.c | 1 - 2 files changed, 2 deletions(-) diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c index 7777804..1e80a0a 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 cc6f379..b0fb654 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. */ -- 2.7.4