Clean up stack growth checks and move them into a common function.

The grows-up and grows-down cases had all the same issues, but
differered in the details. Additionlly, historical evolution of
the tests had caused the result to be pretty unreadable with some
rather long and complex conditionals.

Fix it all up in a more readable helper function.

This also adds the missing RLIMIT_MEMLOCK test.

mm/mmap.c

@@ -1335,13 +1335,60 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
 	return prev ? prev->vm_next : vma;
 }
 
+/*
+ * Verify that the stack growth is acceptable and
+ * update accounting. This is shared with both the
+ * grow-up and grow-down cases.
+ */
+static int acct_stack_growth(struct vm_area_struct * vma, unsigned long size, unsigned long grow)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct rlimit *rlim = current->signal->rlim;
+
+	/* address space limit tests */
+	rlim = current->signal->rlim;
+	if (mm->total_vm + grow > rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT)
+		return -ENOMEM;
+
+	/* Stack limit test */
+	if (size > rlim[RLIMIT_STACK].rlim_cur)
+		return -ENOMEM;
+
+	/* mlock limit tests */
+	if (vma->vm_flags & VM_LOCKED) {
+		unsigned long locked;
+		unsigned long limit;
+		locked = mm->locked_vm + grow;
+		limit = rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
+		if (locked > limit)
+			return -ENOMEM;
+	}
+
+	/*
+	 * Overcommit..  This must be the final test, as it will
+	 * update security statistics.
+	 */
+	if (security_vm_enough_memory(grow))
+		return -ENOMEM;
+
+	/* Ok, everything looks good - let it rip */
+	mm->total_vm += grow;
+	if (vma->vm_flags & VM_LOCKED)
+		mm->locked_vm += grow;
+	__vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);
+	acct_update_integrals();
+	update_mem_hiwater();
+	return 0;
+}
+
 #ifdef CONFIG_STACK_GROWSUP
 /*
  * vma is the first one with address > vma->vm_end.  Have to extend vma.
  */
 int expand_stack(struct vm_area_struct * vma, unsigned long address)
 {
-	unsigned long grow;
+	int error;
+	unsigned long size, grow;
 
 	if (!(vma->vm_flags & VM_GROWSUP))
 		return -EFAULT;
@@ -1361,30 +1408,14 @@ int expand_stack(struct vm_area_struct * vma, unsigned long address)
 	 */
 	address += 4 + PAGE_SIZE - 1;
 	address &= PAGE_MASK;
+	size = address - vma->vm_start;
 	grow = (address - vma->vm_end) >> PAGE_SHIFT;
 
-	/* Overcommit.. */
-	if (security_vm_enough_memory(grow)) {
-		anon_vma_unlock(vma);
-		return -ENOMEM;
-	}
-	
-	if (address - vma->vm_start > current->signal->rlim[RLIMIT_STACK].rlim_cur ||
-			((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) >
-			current->signal->rlim[RLIMIT_AS].rlim_cur) {
-		anon_vma_unlock(vma);
-		vm_unacct_memory(grow);
-		return -ENOMEM;
-	}
-	vma->vm_end = address;
-	vma->vm_mm->total_vm += grow;
-	if (vma->vm_flags & VM_LOCKED)
-		vma->vm_mm->locked_vm += grow;
-	__vm_stat_account(vma->vm_mm, vma->vm_flags, vma->vm_file, grow);
-	acct_update_integrals();
-	update_mem_hiwater();
+	error = acct_stack_growth(vma, size, grow);
+	if (!error)
+		vma->vm_end = address;
 	anon_vma_unlock(vma);
-	return 0;
+	return error;
 }
 
 struct vm_area_struct *
@@ -1409,7 +1440,8 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
  */
 int expand_stack(struct vm_area_struct *vma, unsigned long address)
 {
-	unsigned long grow;
+	int error;
+	unsigned long size, grow;
 
 	/*
 	 * We must make sure the anon_vma is allocated
@@ -1425,31 +1457,16 @@ int expand_stack(struct vm_area_struct *vma, unsigned long address)
 	 * anon_vma lock to serialize against concurrent expand_stacks.
 	 */
 	address &= PAGE_MASK;
+	size = vma->vm_end - address;
 	grow = (vma->vm_start - address) >> PAGE_SHIFT;
 
-	/* Overcommit.. */
-	if (security_vm_enough_memory(grow)) {
-		anon_vma_unlock(vma);
-		return -ENOMEM;
-	}
-	
-	if (vma->vm_end - address > current->signal->rlim[RLIMIT_STACK].rlim_cur ||
-			((vma->vm_mm->total_vm + grow) << PAGE_SHIFT) >
-			current->signal->rlim[RLIMIT_AS].rlim_cur) {
-		anon_vma_unlock(vma);
-		vm_unacct_memory(grow);
-		return -ENOMEM;
+	error = acct_stack_growth(vma, size, grow);
+	if (!error) {
+		vma->vm_start = address;
+		vma->vm_pgoff -= grow;
 	}
-	vma->vm_start = address;
-	vma->vm_pgoff -= grow;
-	vma->vm_mm->total_vm += grow;
-	if (vma->vm_flags & VM_LOCKED)
-		vma->vm_mm->locked_vm += grow;
-	__vm_stat_account(vma->vm_mm, vma->vm_flags, vma->vm_file, grow);
-	acct_update_integrals();
-        update_mem_hiwater();
 	anon_vma_unlock(vma);
-	return 0;
+	return error;
 }
 
 struct vm_area_struct *