uml: simplify helper stack handling

run_helper and run_helper_thread had arguments which were the same in all
callers.  run_helper's stack_out was always NULL and run_helper_thread's
stack_order was always 0.  These are now gone, and the constants folded
into the code.

Also fixed leaks of the helper stack in the AIO and SIGIO code.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 8b81bd5..4d438f3 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -161,7 +161,7 @@
 	 * problem with /dev/net/tun, which if held open by this
 	 * thread, prevents the TUN/TAP device from being reused.
 	 */
-	err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out, 0);
+	err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
 	if(err < 0){
 		printk("fork of winch_thread failed - errno = %d\n", -err);
 		goto out_close;