[PATCH v2 1/2] [md/bitmap] md_bitmap_read_sb uses wrong bitmap blocks

[PATCH v2 1/2] [md/bitmap] md_bitmap_read_sb uses wrong bitmap blocks

[Zhao Heming]

The patched code is used to get chunks number, should use
round-up div to replace current sector_div.
The same code is in md_bitmap_resize():
```
chunks = DIV_ROUND_UP_SECTOR_T(blocks, 1 << chunkshift);
```

Signed-off-by: Zhao Heming <heming.zhao@suse.com>
---
v2:
- change grammar mistake in patch Subject
- fix code syntax error 

---
 drivers/md/md-bitmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index b10c51988c8e..553b6406ba1c 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -605,8 +605,8 @@ static int md_bitmap_read_sb(struct bitmap *bitmap)
 	if (bitmap->cluster_slot >= 0) {
 		sector_t bm_blocks = bitmap->mddev->resync_max_sectors;
 
-		sector_div(bm_blocks,
-			   bitmap->mddev->bitmap_info.chunksize >> 9);
+		bm_blocks = DIV_ROUND_UP_SECTOR_T(bm_blocks,
+			   (bitmap->mddev->bitmap_info.chunksize >> 9));
 		/* bits to bytes */
 		bm_blocks = ((bm_blocks+7) >> 3) + sizeof(bitmap_super_t);
 		/* to 4k blocks */
-- 
2.27.0

[PATCH v2 2/2] [md/bitmap] md_bitmap_get_counter returns wrong blocks

[Zhao Heming]

md_bitmap_get_counter() has code:

```
    if (bitmap->bp[page].hijacked ||
        bitmap->bp[page].map == NULL)
        csize = ((sector_t)1) << (bitmap->chunkshift +
                      PAGE_COUNTER_SHIFT - 1);
```

the minus 1 is wrong, this branch should report 2048 bits of space.
with "-1" action, this only report 1024 bit of space.

this bug code returns wrong blocks, but it doesn't inflence bitmap logic:
1. most callers focus this function return value (the counter of offset),
   not the parameter blocks.
2. the bug is only triggered when hijacked is true or map is NULL.
   the hijacked true condition is very rare.
   the "map == null" only true when array is creating or resizing.
3. even the caller gets wrong blocks, current code makes caller just to
   call md_bitmap_get_counter() one more time.

Signed-off-by: Zhao Heming <heming.zhao@suse.com>
---
v2:
- shorten patch Subject

---
 drivers/md/md-bitmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 553b6406ba1c..11c75e727b49 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1367,7 +1367,7 @@ __acquires(bitmap->lock)
 	if (bitmap->bp[page].hijacked ||
 	    bitmap->bp[page].map == NULL)
 		csize = ((sector_t)1) << (bitmap->chunkshift +
-					  PAGE_COUNTER_SHIFT - 1);
+					  PAGE_COUNTER_SHIFT);
 	else
 		csize = ((sector_t)1) << bitmap->chunkshift;
 	*blocks = csize - (offset & (csize - 1));
-- 
2.27.0

Re: [PATCH v2 1/2] [md/bitmap] md_bitmap_read_sb uses wrong bitmap blocks

[Song Liu]

On Mon, Oct 5, 2020 at 9:02 AM Zhao Heming <heming.zhao@suse.com> wrote:
>
> The patched code is used to get chunks number, should use
> round-up div to replace current sector_div.
> The same code is in md_bitmap_resize():
> ```
> chunks = DIV_ROUND_UP_SECTOR_T(blocks, 1 << chunkshift);
> ```
>
> Signed-off-by: Zhao Heming <heming.zhao@suse.com>

Applied both patches to md-next.

Thanks,
Song