powerpc: 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: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/mm/mmap_64.c b/arch/powerpc/mm/mmap_64.c
index 0d957a4..5a783d8 100644
--- a/arch/powerpc/mm/mmap_64.c
+++ b/arch/powerpc/mm/mmap_64.c
@@ -47,7 +47,7 @@
 	if (current->personality & ADDR_COMPAT_LAYOUT)
 		return 1;
 
-	if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
+	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
 		return 1;
 
 	return sysctl_legacy_va_layout;
@@ -77,7 +77,7 @@
 
 static inline unsigned long mmap_base(void)
 {
-	unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
+	unsigned long gap = rlimit(RLIMIT_STACK);
 
 	if (gap < MIN_GAP)
 		gap = MIN_GAP;