[IA64] use helpers for rlimits

Make sure compiler won't do weird things with limits. E.g. fetching
them twice may return 2 different values after writable limits are
implemented.

I.e. either use rlimit helpers added in
3e10e716abf3c71bdb5d86b8f507f9e72236c9cd
or ACCESS_ONCE if not applicable.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
index b9609c6..7c0d481 100644
--- a/arch/ia64/mm/init.c
+++ b/arch/ia64/mm/init.c
@@ -91,7 +91,7 @@
 inline void
 ia64_set_rbs_bot (void)
 {
-	unsigned long stack_size = current->signal->rlim[RLIMIT_STACK].rlim_max & -16;
+	unsigned long stack_size = rlimit_max(RLIMIT_STACK) & -16;
 
 	if (stack_size > MAX_USER_STACK_SIZE)
 		stack_size = MAX_USER_STACK_SIZE;