mm: constify nmask argument to mbind()

The nmask argument to mbind() is const according to the userspace header
numaif.h, and since the kernel does indeed not modify it, it might as well
be declared const in the kernel.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/syscalls.h

@@ -723,7 +723,7 @@ asmlinkage long sys_move_pages(pid_t pid, unsigned long nr_pages,
 				int flags);
 asmlinkage long sys_mbind(unsigned long start, unsigned long len,
 				unsigned long mode,
-				unsigned long __user *nmask,
+				const unsigned long __user *nmask,
 				unsigned long maxnode,
 				unsigned flags);
 asmlinkage long sys_get_mempolicy(int __user *policy,

mm/mempolicy.c

@@ -1362,7 +1362,7 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 }
 
 SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
-		unsigned long, mode, unsigned long __user *, nmask,
+		unsigned long, mode, const unsigned long __user *, nmask,
 		unsigned long, maxnode, unsigned, flags)
 {
 	nodemask_t nodes;