linux-kernel - [PATCH 4/4] ceph: fix improper use of smp_mb__before

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Date:   Mon, 20 May 2019 19:23:58 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrea Parri <andrea.parri@...rulasolutions.com>,
        stable@...r.kernel.org, "Yan, Zheng" <zyan@...hat.com>,
        Sage Weil <sage@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
        ceph-devel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 4/4] ceph: fix improper use of smp_mb__before_atomic()

This barrier only applies to the read-modify-write operations; in
particular, it does not apply to the atomic64_set() primitive.

Replace the barrier with an smp_mb().

Fixes: fdd4e15838e59 ("ceph: rework dcache readdir")
Cc: stable@...r.kernel.org
Reported-by: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Andrea Parri <andrea.parri@...rulasolutions.com>
Cc: "Yan, Zheng" <zyan@...hat.com>
Cc: Sage Weil <sage@...hat.com>
Cc: Ilya Dryomov <idryomov@...il.com>
Cc: ceph-devel@...r.kernel.org
Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 fs/ceph/super.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 6edab9a750f8a..e02f4ff0be3f1 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -541,7 +541,12 @@ static inline void __ceph_dir_set_complete(struct ceph_inode_info *ci,
 					   long long release_count,
 					   long long ordered_count)
 {
-	smp_mb__before_atomic();
+	/*
+	 * Makes sure operations that setup readdir cache (update page
+	 * cache and i_size) are strongly ordered w.r.t. the following
+	 * atomic64_set() operations.
+	 */
+	smp_mb();
 	atomic64_set(&ci->i_complete_seq[0], release_count);
 	atomic64_set(&ci->i_complete_seq[1], ordered_count);
 }
-- 
2.7.4