linux-kernel - [PATCH RFC tip/core/rcu 08/15] seqlock: Remove now-redundant smp_read_barrier

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Date:   Mon,  9 Oct 2017 17:22:42 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, torvalds@...ux-foundation.org,
        mark.rutland@....com, dhowells@...hat.com,
        linux-arch@...r.kernel.org, peterz@...radead.org,
        will.deacon@....com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: [PATCH RFC tip/core/rcu 08/15] seqlock: Remove now-redundant smp_read_barrier_depends()

READ_ONCE() now implies smp_read_barrier_depends(), so this patch
removes the now-redundant smp_read_barrier_depends() from
raw_read_seqcount_latch().

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
---
 include/linux/seqlock.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index ead97654c4e9..27364347ff68 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -277,9 +277,8 @@ static inline void raw_write_seqcount_barrier(seqcount_t *s)
 
 static inline int raw_read_seqcount_latch(seqcount_t *s)
 {
-	int seq = READ_ONCE(s->sequence);
 	/* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */
-	smp_read_barrier_depends();
+	int seq = READ_ONCE(s->sequence); /* ^^^ */
 	return seq;
 }
 
-- 
2.5.2