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/net_user.c b/arch/um/drivers/net_user.c
index 3503cff..6fa948b 100644
--- a/arch/um/drivers/net_user.c
+++ b/arch/um/drivers/net_user.c
@@ -187,7 +187,7 @@
 	}
 	pe_data.close_me = fds[0];
 	pe_data.stdout = fds[1];
-	pid = run_helper(change_pre_exec, &pe_data, argv, NULL);
+	pid = run_helper(change_pre_exec, &pe_data, argv);
 
 	if (pid > 0)	/* Avoid hang as we won't get data in failure case. */
 		read_output(fds[0], output, output_len);