Btrfs: Add ACCESS_ONCE() to transaction->abort accesses

We may access and update transaction->aborted on the different CPUs without
lock, so we need ACCESS_ONCE() wrapper to prevent the compiler from creating
unsolicited accesses and make sure we can get the right value.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 99545df..d8982e9 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -267,7 +267,7 @@
 			     function, line, errstr);
 		return;
 	}
-	trans->transaction->aborted = errno;
+	ACCESS_ONCE(trans->transaction->aborted) = errno;
 	__btrfs_std_error(root->fs_info, function, line, errno, NULL);
 }
 /*