Commit ee6a6457 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

[PATCH] mm: fixup do_wp_page() 



Wrt. the recent modifications in do_wp_page() Hugh Dickins pointed out:

  "I now realize it's right to the first order (normal case) and to the
   second order (ptrace poke), but not to the third order (ptrace poke
   anon page here to be COWed - perhaps can't occur without intervening
   mprotects)."

This patch restores the old COW behaviour for anonymous pages.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e88dd6c1

mm/memory.c

+13 −6
Original line number Diff line number Diff line
@@ -1467,11 +1467,21 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		goto gotten;



	/*

	 * Only catch write-faults on shared writable pages, read-only

	 * shared pages can get COWed by get_user_pages(.write=1, .force=1).

	 * Take out anonymous pages first, anonymous shared vmas are

	 * not dirty accountable.

	 */

	if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==

	if (PageAnon(old_page)) {

		if (!TestSetPageLocked(old_page)) {

			reuse = can_share_swap_page(old_page);

			unlock_page(old_page);

		}

	} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==

					(VM_WRITE|VM_SHARED))) {

		/*

		 * Only catch write-faults on shared writable pages,

		 * read-only shared pages can get COWed by

		 * get_user_pages(.write=1, .force=1).

		 */

		if (vma->vm_ops && vma->vm_ops->page_mkwrite) {

			/*

			 * Notify the address space that the page is about to
@@ -1503,9 +1513,6 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		dirty_page = old_page;

		get_page(dirty_page);

		reuse = 1;

	} else if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {

		reuse = can_share_swap_page(old_page);

		unlock_page(old_page);

	}



	if (reuse) {

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