Btrfs: fix an oops of log replay

When btrfs recovers from a crash, it may hit the oops below:

------------[ cut here ]------------
kernel BUG at fs/btrfs/inode.c:4580!
[...]
RIP: 0010:[<ffffffffa03df251>]  [<ffffffffa03df251>] btrfs_add_link+0x161/0x1c0 [btrfs]
[...]
Call Trace:
 [<ffffffffa03e7b31>] ? btrfs_inode_ref_index+0x31/0x80 [btrfs]
 [<ffffffffa04054e9>] add_inode_ref+0x319/0x3f0 [btrfs]
 [<ffffffffa0407087>] replay_one_buffer+0x2c7/0x390 [btrfs]
 [<ffffffffa040444a>] walk_down_log_tree+0x32a/0x480 [btrfs]
 [<ffffffffa0404695>] walk_log_tree+0xf5/0x240 [btrfs]
 [<ffffffffa0406cc0>] btrfs_recover_log_trees+0x250/0x350 [btrfs]
 [<ffffffffa0406dc0>] ? btrfs_recover_log_trees+0x350/0x350 [btrfs]
 [<ffffffffa03d18b2>] open_ctree+0x1442/0x17d0 [btrfs]
[...]

This comes from that while replaying an inode ref item, we forget to
check those old conflicting DIR_ITEM and DIR_INDEX items in fs/file tree,
then we will come to conflict corners which lead to BUG_ON().

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Tested-by: Andy Lutomirski <luto@mit.edu>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/tree-log.c

@@ -799,14 +799,15 @@ static noinline int add_inode_ref(struct btrfs_trans_handle *trans,
 				  struct extent_buffer *eb, int slot,
 				  struct btrfs_key *key)
 {
-	struct inode *dir;
-	int ret;
 	struct btrfs_inode_ref *ref;
+	struct btrfs_dir_item *di;
+	struct inode *dir;
 	struct inode *inode;
-	char *name;
-	int namelen;
 	unsigned long ref_ptr;
 	unsigned long ref_end;
+	char *name;
+	int namelen;
+	int ret;
 	int search_done = 0;
 
 	/*
@@ -909,6 +910,25 @@ again:
 	}
 	btrfs_release_path(path);
 
+	/* look for a conflicting sequence number */
+	di = btrfs_lookup_dir_index_item(trans, root, path, btrfs_ino(dir),
+					 btrfs_inode_ref_index(eb, ref),
+					 name, namelen, 0);
+	if (di && !IS_ERR(di)) {
+		ret = drop_one_dir_item(trans, root, path, dir, di);
+		BUG_ON(ret);
+	}
+	btrfs_release_path(path);
+
+	/* look for a conflicing name */
+	di = btrfs_lookup_dir_item(trans, root, path, btrfs_ino(dir),
+				   name, namelen, 0);
+	if (di && !IS_ERR(di)) {
+		ret = drop_one_dir_item(trans, root, path, dir, di);
+		BUG_ON(ret);
+	}
+	btrfs_release_path(path);
+
 insert:
 	/* insert our name */
 	ret = btrfs_add_link(trans, dir, inode, name, namelen, 0,