mm: use mm_struct to resolve gate vma's in __get_user_pages

We now check if a requested user page overlaps a gate vma using the supplied mm
instead of the supplied task.  The given task is now used solely for accounting
purposes and may be NULL.
Signed-off-by: Stephen Wilson <wilsons@start.ca>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

mm/memory.c

@@ -1486,9 +1486,9 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		struct vm_area_struct *vma;
 
 		vma = find_extend_vma(mm, start);
-		if (!vma && in_gate_area(tsk->mm, start)) {
+		if (!vma && in_gate_area(mm, start)) {
 			unsigned long pg = start & PAGE_MASK;
-			struct vm_area_struct *gate_vma = get_gate_vma(tsk->mm);
+			struct vm_area_struct *gate_vma = get_gate_vma(mm);
 			pgd_t *pgd;
 			pud_t *pud;
 			pmd_t *pmd;
@@ -1589,10 +1589,13 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 						return i ? i : -EFAULT;
 					BUG();
 				}
+
+				if (tsk) {
 					if (ret & VM_FAULT_MAJOR)
 						tsk->maj_flt++;
 					else
 						tsk->min_flt++;
+				}
 
 				if (ret & VM_FAULT_RETRY) {
 					*nonblocking = 0;
@@ -1638,7 +1641,8 @@ EXPORT_SYMBOL(__get_user_pages);
 
 /**
  * get_user_pages() - pin user pages in memory
- * @tsk:	task_struct of target task
+ * @tsk:	the task_struct to use for page fault accounting, or
+ *		NULL if faults are not to be recorded.
  * @mm:		mm_struct of target mm
  * @start:	starting user address
  * @nr_pages:	number of pages from start to pin