[PATCH 5.10] btrfs: fix region size in count_bitmap_extents

[Anastasia Belova]

count_bitmap_extents was deleted in version 5.11, but
there is possible mistake in versions 5.6-5.10.

Region size should be calculated by subtracting
the end from the beginning.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: dfb79ddb130e ("btrfs: track discardable extents for async discard")
Signed-off-by: Anastasia Belova <abelova@xxxxxxxxxxxxx>
---
 fs/btrfs/free-space-cache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 4989c60b1df9..a34e266a0969 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -1930,7 +1930,7 @@ static int count_bitmap_extents(struct btrfs_free_space_ctl *ctl,
 
 	bitmap_for_each_set_region(bitmap_info->bitmap, rs, re, 0,
 				   BITS_PER_BITMAP) {
-		bytes -= (rs - re) * ctl->unit;
+		bytes -= (re - rs) * ctl->unit;
 		count++;
 
 		if (!bytes)
-- 
2.30.2