From: Will Deacon <will.deacon@arm.com>
Date: Mon, 19 Feb 2018 14:55:55 +0000
Subject: [PATCH] fs: dcache: Use READ_ONCE when accessing i_dir_seq
Git-commit: 8cc07c808c9d595e81cbe5aad419b7769eb2e5c9
Patch-mainline: v4.16-rc6
References: git-fixes

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>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/dcache.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2492,7 +2492,7 @@ 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;