btrfs: lock the inode first before flushing range when punching hole

When doing hole punching we are flushing delalloc and waiting for ordered
extents to complete before locking the inode (VFS lock and the btrfs
specific i_mmap_lock). This is fine because even if a write happens after
we call btrfs_wait_ordered_range() and before we lock the inode (call
btrfs_inode_lock()), we will notice the write at
btrfs_punch_hole_lock_range() and flush delalloc and wait for its ordered
extent.

We can however make this simpler by locking first the inode an then call
btrfs_wait_ordered_range(), which will allow us to remove the ordered
extent lookup logic from btrfs_punch_hole_lock_range() in the next patch.
It also makes the behaviour the same as plain fallocate, hole punching
and reflinks.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file.c

@@ -2976,11 +2976,12 @@ static int btrfs_punch_hole(struct file *file, loff_t offset, loff_t len)
 	bool truncated_block = false;
 	bool updated_inode = false;
 
+	btrfs_inode_lock(inode, BTRFS_ILOCK_MMAP);
+
 	ret = btrfs_wait_ordered_range(inode, offset, len);
 	if (ret)
-		return ret;
+		goto out_only_mutex;
 
-	btrfs_inode_lock(inode, BTRFS_ILOCK_MMAP);
 	ino_size = round_up(inode->i_size, fs_info->sectorsize);
 	ret = find_first_non_hole(BTRFS_I(inode), &offset, &len);
 	if (ret < 0)