Fix mountpoint reference leakage in linkat

commit d22e6338 upstream.

Recent changes to retry on ESTALE in linkat
(commit 442e31ca)
introduced a mountpoint reference leak and a small memory
leak in case a filesystem link operation returns ESTALE
which is pretty normal for distributed filesystems like
lustre, nfs and so on.
Free old_path in such a case.

[AV: there was another missing path_put() nearby - on the previous
goto retry]

[js: the second path_put is not in 3.12 yet, hunk removed]
Signed-off-by: Oleg Drokin: <green@linuxhacker.ru>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

fs/namei.c

@@ -3924,6 +3924,7 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 out_dput:
 	done_path_create(&new_path, new_dentry);
 	if (retry_estale(error, how)) {
+		path_put(&old_path);
 		how |= LOOKUP_REVAL;
 		goto retry;
 	}