From 4d15f89af0325364bc3051fa0bb8d1be23f87159 Mon Sep 17 00:00:00 2001
From: Julia Cartwright <julia@ni.com>
Date: Thu, 26 Apr 2018 15:02:03 -0500
Subject: [PATCH 408/518] seqlock: provide the same ordering semantics as
 mainline

[ Upstream commit afa4c06b89a3c0fb7784ff900ccd707bef519cb7 ]

The mainline implementation of read_seqbegin() orders prior loads w.r.t.
the read-side critical section.  Fixup the RT writer-boosting
implementation to provide the same guarantee.

Also, while we're here, update the usage of ACCESS_ONCE() to use
READ_ONCE().

Fixes: e69f15cf77c23 ("seqlock: Prevent rt starvation")
Cc: stable-rt@vger.kernel.org
Signed-off-by: Julia Cartwright <julia@ni.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/seqlock.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index ccc8ffb46aac2..92c60384ce1c9 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -469,6 +469,7 @@ static inline unsigned read_seqbegin(seqlock_t *sl)
 		spin_unlock_wait(&sl->lock);
 		goto repeat;
 	}
+	smp_rmb();
 	return ret;
 }
 #endif
-- 
2.41.0

