From d837f7277f56e70d82b3a4a037d744854e62f387 Mon Sep 17 00:00:00 2001
From: Zhao Heming <heming.zhao@suse.com>
Date: Tue, 6 Oct 2020 00:00:24 +0800
Subject: [PATCH] md/bitmap: md_bitmap_get_counter returns wrong blocks
Git-commit: d837f7277f56e70d82b3a4a037d744854e62f387
Patch-mainline: v5.10-rc1
References: bsc#1163727

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>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 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 cd9a12ca281d..b3f13105659d 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1368,7 +1368,7 @@ static bitmap_counter_t *md_bitmap_get_counter(struct bitmap_counts *bitmap,
 	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));
-- 
1.8.3.1