[PATCH v4 3/4] block/badblocks: fix badblocks loss when badblocks combine

[linan666]

From: Li Nan <linan122@xxxxxxxxxx>

badblocks will loss if set it as below:
  $ echo 1 1 > bad_blocks
  $ echo 3 1 > bad_blocks
  $ echo 1 4 > bad_blocks
  $ cat bad_blocks
    1 3

After the fix, in the same scenario, it will be:
  $ cat bad_blocks
    1 4

In badblocks_set(), if set a new badblocks, first find two existing
badblocks adjacent to it, named lo and hi. Then try to merge new with lo.
If merge success and there is an intersection between lo and hi, try to
combine lo and hi.

set 1 4
binary-search:
  lo: 1 1	|____|
  hi: 3 1		  |____|

merge with lo:
  lo: 1 4	|___________________|
  hi: 3 1		  |____|

combine lo and hi:
  result: 1 3	|______________|
			       | -> hi's end
			       |____| -> lost

Now, the end of combined badblocks must be hi's end. However, it should be
the larger one between lo and hi. Fix it.

Fixes: 9e0e252a048b ("badblocks: Add core badblock management code")
Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
 block/badblocks.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/block/badblocks.c b/block/badblocks.c
index 7b1ad364e85c..c1745b76d8f1 100644
--- a/block/badblocks.c
+++ b/block/badblocks.c
@@ -267,16 +267,14 @@ int badblocks_set(struct badblocks *bb, sector_t s, int sectors,
 	if (sectors == 0 && hi < bb->count) {
 		/* we might be able to combine lo and hi */
 		/* Note: 's' is at the end of 'lo' */
-		sector_t a = BB_OFFSET(p[hi]);
-		int lolen = BB_LEN(p[lo]);
-		int hilen = BB_LEN(p[hi]);
-		int newlen = lolen + hilen - (s - a);
+		sector_t a = BB_OFFSET(p[lo]);
+		int newlen = max(s, BB_OFFSET(p[hi]) + BB_LEN(p[hi])) - a;
 
-		if (s >= a && newlen < BB_MAX_LEN) {
+		if (s >= BB_OFFSET(p[hi]) && newlen < BB_MAX_LEN) {
 			/* yes, we can combine them */
 			int ack = BB_ACK(p[lo]) && BB_ACK(p[hi]);
 
-			p[lo] = BB_MAKE(BB_OFFSET(p[lo]), newlen, ack);
+			p[lo] = BB_MAKE(a, newlen, ack);
 			memmove(p + hi, p + hi + 1,
 				(bb->count - hi - 1) * 8);
 			bb->count--;
-- 
2.39.2