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Message-id: <000101d016ad$f0278720$d0769560$%yang@samsung.com>
Date: Sat, 13 Dec 2014 16:21:36 +0800
From: Weijie Yang <weijie.yang@...sung.com>
To: 'Andrew Morton' <akpm@...ux-foundation.org>
Cc: mgorman@...e.de, 'Johannes Weiner' <hannes@...xchg.org>,
'Rik van Riel' <riel@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [RESEND PATCH ] mm: page_alloc: place zone_id check before
VM_BUG_ON_PAGE check
If the freeing page and its buddy page are not at the same zone, the current
holding zone->lock for the freeing page cann't prevent buddy page getting
allocated, this could trigger VM_BUG_ON_PAGE in page_is_buddy() at a
very tiny chance, such as:
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)
zone_1->lock prevents the freeing page getting allocated
zone_2->lock prevents the buddy page getting allocated
they are not the same zone->lock.
If we cann't remove the zone_id check statement, it's better handle
this rare race. This patch fixes this by placing the zone_id check
before the VM_BUG_ON_PAGE check.
Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
Acked-by: Mel Gorman <mgorman@...e.de>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Rik van Riel <riel@...hat.com>
---
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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