md/md-bitmap: fix wrong bitmap_limit for clustermd when write sb

JIRA: https://issues.redhat.com/browse/RHEL-83988

commit 6130825
Author: Su Yue <[email protected]>
Date:   Mon Mar 3 11:39:18 2025 +0800

    md/md-bitmap: fix wrong bitmap_limit for clustermd when write sb

    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: ab99a87 ("md/md-bitmap: fix writing non bitmap pages")
    Signed-off-by: Su Yue <[email protected]>
    Reviewed-by: Heming Zhao <[email protected]>
    Link: https://lore.kernel.org/linux-raid/[email protected]
    Signed-off-by: Yu Kuai <[email protected]>

Signed-off-by: Nigel Croxon <[email protected]>

Author: ncroxon

drivers/md/md-bitmap.c

@@ -428,8 +428,8 @@ 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;
@@ -438,7 +438,7 @@ 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)