[PATCH v2 10/10] Warn cyclic buffer overrun and correct it if possible

[HATAYAMA Daisuke]

(2013/09/11 17:35), HATAYAMA Daisuke wrote:
> (2013/09/11 16:51), Atsushi Kumagai wrote:
>> Hello HATAYAMA-san,
>>
>> (2012/11/16 14:02), HATAYAMA Daisuke wrote:
>>> Clearling bits on cyclic buffer can overrun the cyclic buffer
>>> according to some combination of MAX_ORDER and cyclic buffer size.
>>>
>>> The cyclic buffer size is corrected if possible.
>>>
>>> Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
>>
>> I know it's so late, I found that updating pfn_cyclic is missing.
>> It can cause memory corruption.
>>
>
> Hello Kumagai-san,
>
> Reviewed-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
>
> It might be even better to introduce some kind of helper function that
> sets up these cyclic-mode-related parameters and then to use it in
> initial() and check_cyclic_buffer_overrun().
>

Hello Kumaga-san,

I found one more bug. Could you review it?

 From c98375b9af6c19dff88823166eaf13674b4a47ec Mon Sep 17 00:00:00 2001
From: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
Date: Thu, 12 Sep 2013 10:35:17 +0900
Subject: [PATCH] Use divideup() to calculate maximum required bitmap size

Currently, check_cyclic_buffer_overrun() wrongly calculates maximum
bitmap size required to represent maximum block size managed by buddy
allocator with roundup(). Then, max_block_size is BITPERBYTE-time
larger than its correct size. As a result, although the bug never
affect free-page filtering since roundup(max_order_nr_pages,
BITPERBYTE) is a multiple of divideup(max_order_nr_pages, BITPERBYTE),
the following sanity check, (max_block_size > info->bufsize_cyclic),
and recalculation of info->bufsize_cyclic becomes BITPERBYTE-time
conservative and inefficient.

Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
---
  makedumpfile.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 164b3f1..e66c494 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -4078,10 +4078,10 @@ check_cyclic_buffer_overrun(void)
  {
  	int max_order = ARRAY_LENGTH(zone.free_area);
  	int max_order_nr_pages = 1 << (max_order - 1);
-	unsigned long max_block_size = roundup(max_order_nr_pages, BITPERBYTE);
+	unsigned long max_block_size = divideup(max_order_nr_pages,
+						BITPERBYTE);
  
-	if (info->bufsize_cyclic %
-	    roundup(max_order_nr_pages, BITPERBYTE)) {
+	if (info->bufsize_cyclic % max_block_size) {
  		unsigned long bufsize;
  
  		if (max_block_size > info->bufsize_cyclic) {
-- 
1.8.3.1



-- 
Thanks.
HATAYAMA, Daisuke