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do_wp_page: fix regression with execute in place

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Fix do_wp_page for VM_MIXEDMAP mappings.

In the case where pfn_valid returns 0 for a pfn at the beginning of
do_wp_page and the mapping is not shared writable, the code branches to
label `gotten:' with old_page == NULL.

In case the vma is locked (vma->vm_flags & VM_LOCKED), lock_page,
clear_page_mlock, and unlock_page try to access the old_page.

This patch checks whether old_page is valid before it is dereferenced.

The regression was introduced by "mlock: mlocked pages are unevictable"
(commit b291f00039).

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: <stable@kernel.org>		[2.6.28.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Carsten Otte 2009-02-04 15:12:16 -08:00 committed by Linus Torvalds
parent 777c6c5f1f
commit ab92661d5d
1 changed files with 1 additions and 1 deletions
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2
mm/memory.c
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@ -1999,7 +1999,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
* Don't let another task, with possibly unlocked vma,
* keep the mlocked page.
*/
if (vma->vm_flags & VM_LOCKED) {
if ((vma->vm_flags & VM_LOCKED) && old_page) {
lock_page(old_page); /* for LRU manipulation */
clear_page_mlock(old_page);
unlock_page(old_page);