udf: Fix lockdep warning from udf_symlink()

Lockdep is complaining about UDF:
=============================================
[ INFO: possible recursive locking detected ]
3.12.0+ #16 Not tainted
---------------------------------------------
ln/7386 is trying to acquire lock:
 (&ei->i_data_sem){+.+...}, at: [<ffffffff8142f06d>] udf_get_block+0x8d/0x130

but task is already holding lock:
 (&ei->i_data_sem){+.+...}, at: [<ffffffff81431a8d>] udf_symlink+0x8d/0x690

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&ei->i_data_sem);
  lock(&ei->i_data_sem);

 *** DEADLOCK ***

This is because we hold i_data_sem of the symlink inode while calling
udf_add_entry() for the directory. I don't think this can ever lead to
deadlocks since we never hold i_data_sem for two inodes in any other
place.

The fix is simple - move unlock of i_data_sem for symlink inode up. We
don't need it for anything when linking symlink inode to directory.

Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/namei.c

@@ -1010,6 +1010,7 @@ static int udf_symlink(struct inode *dir, struct dentry *dentry,
 	else
 		udf_truncate_tail_extent(inode);
 	mark_inode_dirty(inode);
+	up_write(&iinfo->i_data_sem);
 
 	fi = udf_add_entry(dir, dentry, &fibh, &cfi, &err);
 	if (!fi)
@@ -1023,7 +1024,6 @@ static int udf_symlink(struct inode *dir, struct dentry *dentry,
 	udf_write_fi(dir, &cfi, fi, &fibh, NULL, NULL);
 	if (UDF_I(dir)->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB)
 		mark_inode_dirty(dir);
-	up_write(&iinfo->i_data_sem);
 	if (fibh.sbh != fibh.ebh)
 		brelse(fibh.ebh);
 	brelse(fibh.sbh);