lkml.org 
[lkml]   [2014]   [Dec]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RESEND PATCH ] mm: page_alloc: place zone_id check before VM_BUG_ON_PAGE check
Date
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@samsung.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.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



\
 
 \ /
  Last update: 2014-12-13 10:01    [W:0.093 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site