3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vlastimil Babka <vbabka@xxxxxxx>
commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c upstream.
A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin
fuzzing with trinity. The call site try_to_unmap_cluster() does not lock
the pages other than its check_page parameter (which is already locked).
The BUG_ON in mlock_vma_page() is not documented and its purpose is
somewhat unclear, but apparently it serializes against page migration,
which could otherwise fail to transfer the PG_mlocked flag. This would
not be fatal, as the page would be eventually encountered again, but
NR_MLOCK accounting would become distorted nevertheless. This patch adds
a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that
effect.
The call site try_to_unmap_cluster() is fixed so that for page !=
check_page, trylock_page() is attempted (to avoid possible deadlocks as we
already have check_page locked) and mlock_vma_page() is performed only
upon success. If the page lock cannot be obtained, the page is left
without PG_mlocked, which is again not a problem in the whole unevictable
memory design.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Yijing Wang <wangyijing@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/mlock.c | 2 ++
mm/rmap.c | 14 ++++++++++++--
2 files changed, 14 insertions(+), 2 deletions(-)
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -78,6 +78,7 @@ void __clear_page_mlock(struct page *pag
*/
void mlock_vma_page(struct page *page)
{
+ /* Serialize with page migration */
BUG_ON(!PageLocked(page));
if (!TestSetPageMlocked(page)) {
@@ -105,6 +106,7 @@ void mlock_vma_page(struct page *page)
*/
void munlock_vma_page(struct page *page)
{
+ /* For try_to_munlock() and to serialize with page migration */
BUG_ON(!PageLocked(page));
if (TestClearPageMlocked(page)) {
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1449,9 +1449,19 @@ static int try_to_unmap_cluster(unsigned
BUG_ON(!page || PageAnon(page));
if (locked_vma) {
- mlock_vma_page(page); /* no-op if already mlocked */
- if (page == check_page)
+ if (page == check_page) {
+ /* we know we have check_page locked */
+ mlock_vma_page(page);
ret = SWAP_MLOCK;
+ } else if (trylock_page(page)) {
+ /*
+ * If we can lock the page, perform mlock.
+ * Otherwise leave the page alone, it will be
+ * eventually encountered again later.
+ */
+ mlock_vma_page(page);
+ unlock_page(page);
+ }
continue; /* don't unmap */
}
--
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