usermodehelper: cleanup/fix __orderly_poweroff() && argv_free()

__orderly_poweroff() does argv_free() if call_usermodehelper_fns()
returns -ENOMEM.  As Lucas pointed out, this can be wrong if -ENOMEM was
not triggered by the failing call_usermodehelper_setup(), in this case
both __orderly_poweroff() and argv_cleanup() can do kfree().

Kill argv_cleanup() and change __orderly_poweroff() to call argv_free()
unconditionally like do_coredump() does.  This info->cleanup() is not
needed (and wrong) since 6c0c0d4d "fix bug in orderly_poweroff() which
did the UMH_NO_WAIT => UMH_WAIT_EXEC change, we can rely on the fact
that CLONE_VFORK can't return until do_execve() succeeds/fails.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Cc: David Howells <dhowells@redhat.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: hongfeng <hongfeng@marvell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys.c

@@ -2185,11 +2185,6 @@ SYSCALL_DEFINE3(getcpu, unsigned __user *, cpup, unsigned __user *, nodep,
 
 char poweroff_cmd[POWEROFF_CMD_PATH_LEN] = "/sbin/poweroff";
 
-static void argv_cleanup(struct subprocess_info *info)
-{
-	argv_free(info->argv);
-}
-
 static int __orderly_poweroff(void)
 {
 	int argc;
@@ -2209,9 +2204,8 @@ static int __orderly_poweroff(void)
 	}
 
 	ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_WAIT_EXEC,
-				      NULL, argv_cleanup, NULL);
-	if (ret == -ENOMEM)
-		argv_free(argv);
+				      NULL, NULL, NULL);
+	argv_free(argv);
 
 	return ret;
 }