If the free page and its buddy has different zone id, the current
zone->lock cann't prevent buddy page getting allocated, this could
trigger VM_BUG_ON_PAGE in a very tiny chance:
cpu 0: cpu 1:
hold zone_1 lock
check page and it buddy
PageBuddy(buddy) is true hold zone_2 lock
page_order(buddy) == order is true alloc buddy
trigger VM_BUG_ON_PAGE(page_count(buddy) != 0)
This patch fixes this issue by placing the zone id check before
the VM_BUG_ON_PAGE check.
Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
---
mm/page_alloc.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 616a2c9..491d055 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -488,17 +488,15 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
return 0;
if (page_is_guard(buddy) && page_order(buddy) == order) {
- VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
-
if (page_zone_id(page) != page_zone_id(buddy))
return 0;
+ VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
+
return 1;
}
if (PageBuddy(buddy) && page_order(buddy) == order) {
- VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
-
/*
* zone check is done late to avoid uselessly
* calculating zone/node ids for pages that could
@@ -507,6 +505,8 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
if (page_zone_id(page) != page_zone_id(buddy))
return 0;
+ VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
+
return 1;
}
return 0;
--
1.7.10.4
--
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