From: Will Deacon <will.deacon@arm.com>
Date: Mon, 19 Feb 2018 14:55:55 +0000 (+0000)
Subject: fs: dcache: Use READ_ONCE when accessing i_dir_seq
X-Git-Tag: v4.16-rc6~10^2~1
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=8cc07c808c9d595e81cbe5aad419b7769eb2e5c9;p=people%2Froyger%2Flinux.git

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@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/dcache.c b/fs/dcache.c
index bde3b6662601..8945e6cabd93 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2507,7 +2507,7 @@ retry:
 	}
 
 	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;