From: Hugh Dickins <hughd@xxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit c0d73261f5c1355a35b8b40e871d31578ce0c044 upstream.
Use ACCESS_ONCE() in handle_pte_fault() when getting the entry or
orig_pte upon which all subsequent decisions and pte_same() tests will
be made.
I have no evidence that its lack is responsible for the mm/filemap.c:202
BUG_ON(page_mapped(page)) in __delete_from_page_cache() found by
trinity, and I am not optimistic that it will fix it. But I have found
no other explanation, and ACCESS_ONCE() here will surely not hurt.
If gcc does re-access the pte before passing it down, then that would be
disastrous for correct page fault handling, and certainly could explain
the page_mapped() BUGs seen (concurrent fault causing page to be mapped
in a second time on top of itself: mapcount 2 for a single pte).
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 99fe3aa1035c..b870c9c5c89b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3698,7 +3698,7 @@ static int handle_pte_fault(struct mm_struct *mm,
pte_t entry;
spinlock_t *ptl;
- entry = *pte;
+ entry = ACCESS_ONCE(*pte);
if (!pte_present(entry)) {
if (pte_none(entry)) {
if (vma->vm_ops) {
--
2.1.0
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