Commit 68804cf1 authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Paul E. McKenney
Browse files

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: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent ae5c2341

kernel/rcu/rcu_segcblist.c

+0 −1
Original line number Diff line number Diff line
@@ -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);

kernel/rcu/tree.c

+0 −1
Original line number Diff line number Diff line
@@ -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. */