mm/mmap.c: add mlock_future_check() helper

Both do_brk and do_mmap_pgoff verify that we are actually capable of
locking future pages if the corresponding VM_LOCKED flags are used.
Encapsulate this logic into a single mlock_future_check() helper
function.
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: Michel Lespinasse <walken@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -1191,6 +1191,24 @@ static inline unsigned long round_hint_to_min(unsigned long hint)
 	return hint;
 }
 
+static inline int mlock_future_check(struct mm_struct *mm,
+				     unsigned long flags,
+				     unsigned long len)
+{
+	unsigned long locked, lock_limit;
+
+	/*  mlock MCL_FUTURE? */
+	if (flags & VM_LOCKED) {
+		locked = len >> PAGE_SHIFT;
+		locked += mm->locked_vm;
+		lock_limit = rlimit(RLIMIT_MEMLOCK);
+		lock_limit >>= PAGE_SHIFT;
+		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+			return -EAGAIN;
+	}
+	return 0;
+}
+
 /*
  * The caller must hold down_write(&current->mm->mmap_sem).
  */
@@ -1252,16 +1270,8 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 		if (!can_do_mlock())
 			return -EPERM;
 
-	/* mlock MCL_FUTURE? */
-	if (vm_flags & VM_LOCKED) {
-		unsigned long locked, lock_limit;
-		locked = len >> PAGE_SHIFT;
-		locked += mm->locked_vm;
-		lock_limit = rlimit(RLIMIT_MEMLOCK);
-		lock_limit >>= PAGE_SHIFT;
-		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+	if (mlock_future_check(mm, vm_flags, len))
 		return -EAGAIN;
-	}
 
 	if (file) {
 		struct inode *inode = file_inode(file);
@@ -2592,18 +2602,9 @@ static unsigned long do_brk(unsigned long addr, unsigned long len)
 	if (error & ~PAGE_MASK)
 		return error;
 
-	/*
-	 * mlock MCL_FUTURE?
-	 */
-	if (mm->def_flags & VM_LOCKED) {
-		unsigned long locked, lock_limit;
-		locked = len >> PAGE_SHIFT;
-		locked += mm->locked_vm;
-		lock_limit = rlimit(RLIMIT_MEMLOCK);
-		lock_limit >>= PAGE_SHIFT;
-		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
-			return -EAGAIN;
-	}
+	error = mlock_future_check(mm, mm->def_flags, len);
+	if (error)
+		return error;
 
 	/*
 	 * mm->mmap_sem is required to protect against another thread