Re: [PATCH v3] md/md-bitmap: fix wrong bitmap_limit for clustermd when write sb

[Su Yue <l@damenly.org>]

On Wed 05 Mar 2025 at 09:25, Yu Kuai <yukuai1@huaweicloud.com> 
wrote:

> 在 2025/03/03 11:39, Su Yue 写道:
>> In clustermd, separate write-intent-bitmaps are used for each 
>> cluster
>> node:
>> 0                    4k                     8k 
>> 12k
>> -------------------------------------------------------------------
>> | idle                | md super            | bm super [0] + 
>> bits |
>> | bm bits[0, contd]   | bm super[1] + bits  | bm bits[1, contd] 
>> |
>> | bm super[2] + bits  | bm bits [2, contd]  | bm super[3] + 
>> bits  |
>> | bm bits [3, contd]  |                     | 
>> |
>> So in node 1, pg_index in __write_sb_page() could equal to
>> bitmap->storage.file_pages. Then bitmap_limit will be 
>> calculated to
>> 0. md_super_write() will be called with 0 size.
>> That means the first 4k sb area of node 1 will never be updated
>> through filemap_write_page().
>> This bug causes hang of mdadm/clustermd_tests/01r1_Grow_resize.
>> Here use (pg_index % bitmap->storage.file_pages) to make 
>> calculation
>> of bitmap_limit correct.
>> Fixes: ab99a87542f1 ("md/md-bitmap: fix writing non bitmap 
>> pages")
>> Signed-off-by: Su Yue <glass.su@suse.com>
>> ---
>> Changelog:
>> v3:
>>      Amend commit message suggested by Heming.
>> v2:
>>      Remove unintended change calling md_super_write().
>> ---
>>   drivers/md/md-bitmap.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>
> Applied to md-6.15
>
Since it's a bug fix, could you please queue it to 6.14 if the 
merge window
is still open?

--
Su
> Thanks,
>> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
>> index 23c09d22fcdb..9ae6cc8e30cb 100644
>> --- a/drivers/md/md-bitmap.c
>> +++ b/drivers/md/md-bitmap.c
>> @@ -426,8 +426,8 @@ static int __write_sb_page(struct md_rdev 
>> *rdev, struct bitmap *bitmap,
>>   	struct block_device *bdev;
>>   	struct mddev *mddev = bitmap->mddev;
>>   	struct bitmap_storage *store = &bitmap->storage;
>> -	unsigned int bitmap_limit = (bitmap->storage.file_pages - 
>> pg_index) <<
>> -		PAGE_SHIFT;
>> +	unsigned long num_pages = bitmap->storage.file_pages;
>> +	unsigned int bitmap_limit = (num_pages - pg_index % 
>> num_pages) << PAGE_SHIFT;
>>   	loff_t sboff, offset = mddev->bitmap_info.offset;
>>   	sector_t ps = pg_index * PAGE_SIZE / SECTOR_SIZE;
>>   	unsigned int size = PAGE_SIZE;
>> @@ -436,7 +436,7 @@ static int __write_sb_page(struct md_rdev 
>> *rdev, struct bitmap *bitmap,
>>     	bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;
>>   	/* we compare length (page numbers), not page offset. */
>> -	if ((pg_index - store->sb_index) == store->file_pages - 1) 
>> {
>> +	if ((pg_index - store->sb_index) == num_pages - 1) {
>>   		unsigned int last_page_size = store->bytes & 
>>   (PAGE_SIZE - 1);
>>     		if (last_page_size == 0)
>>