afs: Fix the nlink handling of dir-over-dir rename

Fix rename of one directory over another such that the nlink on the deleted
directory is cleared to 0 rather than being decremented to 1.

This was causing the generic/035 xfstest to fail.

Fixes: e49c7b2 ("afs: Build an abstraction around an "operation" concept")
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/162194384460.3999479.7605572278074191079.stgit@warthog.procyon.org.uk/ # v1
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/afs/dir.c

@@ -1919,7 +1919,9 @@ static void afs_rename_edit_dir(struct afs_operation *op)
 	new_inode = d_inode(new_dentry);
 	if (new_inode) {
 		spin_lock(&new_inode->i_lock);
-		if (new_inode->i_nlink > 0)
+		if (S_ISDIR(new_inode->i_mode))
+			clear_nlink(new_inode);
+		else if (new_inode->i_nlink > 0)
 			drop_nlink(new_inode);
 		spin_unlock(&new_inode->i_lock);
 	}