badblocks: fix merge issue when new badblocks align with pre+1

There is a merge issue when adding badblocks as follow:
  echo 0 10 > bad_blocks
  echo 30 10 > bad_blocks
  echo 20 10 > bad_blocks
  cat bad_blocks
  0 10
  20 10    //should be merged with (30 10)
  30 10

In this case, if new badblocks does not intersect with prev, it is added
by insert_at(). If there is an intersection with prev+1, the merge will
be processed in the next re_insert loop.

However, when the end of the new badblocks is exactly equal to the offset
of prev+1, no further re_insert loop occurs, and the two badblocks are not
merge.

Fix it by inc prev, badblocks can be merged during the subsequent code.

Fixes: aa511ff ("badblocks: switch to the improved badblock handling code")
Signed-off-by: Li Nan <[email protected]>
Reviewed-by: Yu Kuai <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Li Nan

block/badblocks.c

@@ -892,7 +892,7 @@ static int _badblocks_set(struct badblocks *bb, sector_t s, int sectors,
 		len = insert_at(bb, 0, &bad);
 		bb->count++;
 		added++;
-		hint = 0;
+		hint = ++prev;
 		goto update_sectors;
 	}
 
@@ -947,7 +947,7 @@ static int _badblocks_set(struct badblocks *bb, sector_t s, int sectors,
 	len = insert_at(bb, prev + 1, &bad);
 	bb->count++;
 	added++;
-	hint = prev + 1;
+	hint = ++prev;
 
 update_sectors:
 	s += len;