linux-kernel - [PATCH v2 2/2] fs: dcache: Use READ_ONCE when accessing i_dir

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Message-Id: <1519052155-6361-3-git-send-email-will.deacon@arm.com>
Date:   Mon, 19 Feb 2018 14:55:55 +0000
From:   Will Deacon <will.deacon@....com>
To:     linux-fsdevel@...r.kernel.org
Cc:     peterz@...radead.org, viro@...iv.linux.org.uk, willy@...radead.org,
        linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>
Subject: [PATCH v2 2/2] fs: dcache: Use READ_ONCE when accessing i_dir_seq

i_dir_seq is subject to concurrent modification by a cmpxchg or
store-release operation, so ensure that the relaxed access in
d_alloc_parallel uses READ_ONCE.

Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Will Deacon <will.deacon@....com>
---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index b243deec298c..5716ab04e1db 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2502,7 +2502,7 @@ struct dentry *d_alloc_parallel(struct dentry *parent,
 	}
 
 	hlist_bl_lock(b);
-	if (unlikely(parent->d_inode->i_dir_seq != seq)) {
+	if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
 		hlist_bl_unlock(b);
 		rcu_read_unlock();
 		goto retry;
-- 
2.1.4