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

[Heming Zhao <heming.zhao@suse.com>]

On 3/3/25 11:39, Su Yue wrote:
> 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>

Looks good to me
Reviewed-by: Heming Zhao <heming.zhao@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(-)
> 
> 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)