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authorMel Gorman <mel@csn.ul.ie>2010-10-26 14:21:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-26 16:52:03 -0700
commitb7f50cfa3630b6e079929ffccfd442d65064ee1f (patch)
treeb6f28ed350055bb864cbe317284eb56fca29cfc3 /mm
parenta75d377686037982cbec320bb770b19fe7be6a5d (diff)
downloadvexpress-lsk-b7f50cfa3630b6e079929ffccfd442d65064ee1f.tar.gz
mm, page-allocator: do not check the state of a non-existant buddy during free
There is a bug in commit 6dda9d55 ("page allocator: reduce fragmentation in buddy allocator by adding buddies that are merging to the tail of the free lists") that means a buddy at order MAX_ORDER is checked for merging. A page of this order never exists so at times, an effectively random piece of memory is being checked. Alan Curry has reported that this is causing memory corruption in userspace data on a PPC32 platform (http://lkml.org/lkml/2010/10/9/32). It is not clear why this is happening. It could be a cache coherency problem where pages mapped in both user and kernel space are getting different cache lines due to the bad read from kernel space (http://lkml.org/lkml/2010/10/13/179). It could also be that there are some special registers being io-remapped at the end of the memmap array and that a read has special meaning on them. Compiler bugs have been ruled out because the assembly before and after the patch looks relatively harmless. This patch fixes the problem by ensuring we are not reading a possibly invalid location of memory. It's not clear why the read causes corruption but one way or the other it is a buggy read. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Corrado Zoccolo <czoccolo@gmail.com> Reported-by: Alan Curry <pacman@kosh.dhis.org> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: Rik van Riel <riel@redhat.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page_alloc.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2a362c52fdf..5faf876cfc3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -531,7 +531,7 @@ static inline void __free_one_page(struct page *page,
* so it's less likely to be used soon and more likely to be merged
* as a higher order page
*/
- if ((order < MAX_ORDER-1) && pfn_valid_within(page_to_pfn(buddy))) {
+ if ((order < MAX_ORDER-2) && pfn_valid_within(page_to_pfn(buddy))) {
struct page *higher_page, *higher_buddy;
combined_idx = __find_combined_index(page_idx, order);
higher_page = page + combined_idx - page_idx;