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Subject[patch 02/53] do_wp_page: fix regression with execute in place
2.6.28-stable review patch.  If anyone has any objections, please let us know.
------------------

From: Carsten Otte <cotte@de.ibm.com>

commit ab92661d5d9514647346047f30f67a7f35ffea67 upstream.

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 b291f000393f5a0b679012b39d79fbc85c018233).

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1881,7 +1881,7 @@ gotten:
* 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);


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