Re: [PATCH v2] md/md-bitmap: fix wrong bitmap_limit for clustermd when write sb

[Glass Su <glass.su@suse.com>]

> On Mar 3, 2025, at 11:08, Heming Zhao <heming.zhao@suse.com> wrote:
> 
> Hi Glass,
> 
> The code looks good to me.
> The commit log needs to be revised.
> 
> On 3/2/25 12:39, Su Yue wrote:
>> In clustermd, Separate write-intent-bitmaps are used for each cluster
>> node:
> 
> Change 'Separate' to lowercase 'separate'.
>> 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 node the first 4k sb area of node 1 will never be updated
>> through filemap_write_page().
> 
> "That means node the ...", should remove the word 'node'?

Thanks. Fixed in v3.

— 
Su
> 
> - Heming
> 
>> This bug causes hang of mdadm/clustermd_tests/01r1_Grow_resize.
>> Here use (pg_index % bitmap->storage.file_pages) to calculation of
>> bitmap_limit correct.
>> Fixes: ab99a87542f1 ("md/md-bitmap: fix writing non bitmap pages")
>> Signed-off-by: Su Yue <glass.su@suse.com>
>> ---
>>  drivers/md/md-bitmap.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>> 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)
>