memsw: handle swapaccount kernel parameter correctly

__setup based kernel command line parameters handlers which are handled in
obsolete_checksetup are provided with the parameter value including =
(more precisely everything right after the parameter name).

This means that the current implementation of swapaccount[=1|0] doesn't
work at all because if there is a value for the parameter then we are
testing for "0" resp.  "1" but we are getting "=0" resp.  "=1" and if
there is no parameter value we are getting an empty string rather than
NULL.

The original noswapccount parameter, which doesn't care about the value,
works correctly.

Signed-off-by: Michal Hocko <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Daisuke Nishimura <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memcontrol.c

@@ -5024,17 +5024,17 @@ struct cgroup_subsys mem_cgroup_subsys = {
 static int __init enable_swap_account(char *s)
 {
 	/* consider enabled if no parameter or 1 is given */
-	if (!s || !strcmp(s, "1"))
+	if (!(*s) || !strcmp(s, "=1"))
 		really_do_swap_account = 1;
-	else if (!strcmp(s, "0"))
+	else if (!strcmp(s, "=0"))
 		really_do_swap_account = 0;
 	return 1;
 }
 __setup("swapaccount", enable_swap_account);
 
 static int __init disable_swap_account(char *s)
 {
-	enable_swap_account("0");
+	enable_swap_account("=0");
 	return 1;
 }
 __setup("noswapaccount", disable_swap_account);