mm: use rlimit helpers

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
3e10e716ab ("resource: add helpers for
fetching rlimits") or ACCESS_ONCE if not applicable.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mlock.c

@@ -25,7 +25,7 @@ int can_do_mlock(void)
 {
 	if (capable(CAP_IPC_LOCK))
 		return 1;
-	if (current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur != 0)
+	if (rlimit(RLIMIT_MEMLOCK) != 0)
 		return 1;
 	return 0;
 }
@@ -487,7 +487,7 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 	locked = len >> PAGE_SHIFT;
 	locked += current->mm->locked_vm;
 
-	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
+	lock_limit = rlimit(RLIMIT_MEMLOCK);
 	lock_limit >>= PAGE_SHIFT;
 
 	/* check against resource limits */
@@ -550,7 +550,7 @@ SYSCALL_DEFINE1(mlockall, int, flags)
 
 	down_write(&current->mm->mmap_sem);
 
-	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
+	lock_limit = rlimit(RLIMIT_MEMLOCK);
 	lock_limit >>= PAGE_SHIFT;
 
 	ret = -ENOMEM;
@@ -584,7 +584,7 @@ int user_shm_lock(size_t size, struct user_struct *user)
 	int allowed = 0;
 
 	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
-	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
+	lock_limit = rlimit(RLIMIT_MEMLOCK);
 	if (lock_limit == RLIM_INFINITY)
 		allowed = 1;
 	lock_limit >>= PAGE_SHIFT;
@@ -618,12 +618,12 @@ int account_locked_memory(struct mm_struct *mm, struct rlimit *rlim,
 
 	down_write(&mm->mmap_sem);
 
-	lim = rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
+	lim = ACCESS_ONCE(rlim[RLIMIT_AS].rlim_cur) >> PAGE_SHIFT;
 	vm   = mm->total_vm + pgsz;
 	if (lim < vm)
 		goto out;
 
-	lim = rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
+	lim = ACCESS_ONCE(rlim[RLIMIT_MEMLOCK].rlim_cur) >> PAGE_SHIFT;
 	vm   = mm->locked_vm + pgsz;
 	if (lim < vm)
 		goto out;