call_usermodehelper: simplify/fix UMH_NO_WAIT case

__call_usermodehelper(UMH_NO_WAIT) has 2 problems:

	- if kernel_thread() fails, call_usermodehelper_freeinfo()
	  is not called.

	- for unknown reason UMH_NO_WAIT has UMH_WAIT_PROC logic,
	  we spawn yet another thread which waits until the user
	  mode application exits.

Change the UMH_NO_WAIT code to use ____call_usermodehelper() instead of
wait_for_helper(), and do call_usermodehelper_freeinfo() unconditionally.
We can rely on CLONE_VFORK, do_fork(CLONE_VFORK) until the child exits or
execs.

With or without this patch UMH_NO_WAIT does not report the error if
kernel_thread() fails, this is correct since the caller doesn't wait for
result.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kmod.c

@@ -205,10 +205,7 @@ static int wait_for_helper(void *data)
 			sub_info->retval = ret;
 	}
 
-	if (sub_info->wait == UMH_NO_WAIT)
-		call_usermodehelper_freeinfo(sub_info);
-	else
-		complete(sub_info->complete);
+	complete(sub_info->complete);
 	return 0;
 }
 
@@ -217,13 +214,13 @@ static void __call_usermodehelper(struct work_struct *work)
 {
 	struct subprocess_info *sub_info =
 		container_of(work, struct subprocess_info, work);
-	pid_t pid;
 	enum umh_wait wait = sub_info->wait;
+	pid_t pid;
 
 	/* CLONE_VFORK: wait until the usermode helper has execve'd
 	 * successfully We need the data structures to stay around
 	 * until that is done.  */
-	if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
+	if (wait == UMH_WAIT_PROC)
 		pid = kernel_thread(wait_for_helper, sub_info,
 				    CLONE_FS | CLONE_FILES | SIGCHLD);
 	else
@@ -232,6 +229,7 @@ static void __call_usermodehelper(struct work_struct *work)
 
 	switch (wait) {
 	case UMH_NO_WAIT:
+		call_usermodehelper_freeinfo(sub_info);
 		break;
 
 	case UMH_WAIT_PROC: