Revert "mm: keep a guard page below a grow-down stack segment"

This reverts commit dabebaedfe.

mm/memory.c

@@ -2611,26 +2611,6 @@ out_page:
 	return ret;
 }
 
-/*
- * This is like a special single-page "expand_downwards()",
- * except we must first make sure that 'address-PAGE_SIZE'
- * doesn't hit another vma.
- *
- * The "find_vma()" will do the right thing even if we wrap
- */
-static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned long address)
-{
-	address &= PAGE_MASK;
-	if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
-		address -= PAGE_SIZE;
-		if (find_vma(vma->vm_mm, address) != vma)
-			return -ENOMEM;
-
-		expand_stack(vma, address);
-	}
-	return 0;
-}
-
 /*
  * We enter with non-exclusive mmap_sem (to exclude vma changes,
  * but allow concurrent faults), and pte mapped but not yet locked.
@@ -2644,19 +2624,6 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	spinlock_t *ptl;
 	pte_t entry;
 
-	if (check_stack_guard_page(vma, address) < 0)
-		return VM_FAULT_SIGBUS;
-
-	if (!(flags & FAULT_FLAG_WRITE)) {
-		entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
-						vma->vm_page_prot));
-		ptl = pte_lockptr(mm, pmd);
-		spin_lock(ptl);
-		if (!pte_none(*page_table))
-			goto unlock;
-		goto setpte;
-	}
-
 	/* Allocate our own private page. */
 	pte_unmap(page_table);