badblocks: fix missing bad blocks on retry in _badblocks_check()

The bad blocks check would miss bad blocks when retrying under contention,
as checking parameters are not reset. These stale values from the previous
attempt could lead to incorrect scanning in the subsequent retry.

Move seqlock to outer function and reinitialize checking state for each
retry. This ensures a clean state for each check attempt, preventing any
missed bad blocks.

Fixes: 3ea3354 ("badblocks: improve badblocks_check() for multiple ranges handling")
Signed-off-by: Zheng Qixing <[email protected]>
Reviewed-by: Yu Kuai <[email protected]>
Acked-by: Coly Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Zheng Qixing

block/badblocks.c

@@ -1191,31 +1191,12 @@ static int _badblocks_clear(struct badblocks *bb, sector_t s, int sectors)
 static int _badblocks_check(struct badblocks *bb, sector_t s, int sectors,
 			    sector_t *first_bad, int *bad_sectors)
 {
-	int unacked_badblocks, acked_badblocks;
 	int prev = -1, hint = -1, set = 0;
 	struct badblocks_context bad;
-	unsigned int seq;
+	int unacked_badblocks = 0;
+	int acked_badblocks = 0;
+	u64 *p = bb->page;
 	int len, rv;
-	u64 *p;
-
-	WARN_ON(bb->shift < 0 || sectors == 0);
-
-	if (bb->shift > 0) {
-		sector_t target;
-
-		/* round the start down, and the end up */
-		target = s + sectors;
-		rounddown(s, 1 << bb->shift);
-		roundup(target, 1 << bb->shift);
-		sectors = target - s;
-	}
-
-retry:
-	seq = read_seqbegin(&bb->lock);
-
-	p = bb->page;
-	unacked_badblocks = 0;
-	acked_badblocks = 0;
 
 re_check:
 	bad.start = s;
@@ -1281,9 +1262,6 @@ static int _badblocks_check(struct badblocks *bb, sector_t s, int sectors,
 	else
 		rv = 0;
 
-	if (read_seqretry(&bb->lock, seq))
-		goto retry;
-
 	return rv;
 }
 
@@ -1324,7 +1302,27 @@ static int _badblocks_check(struct badblocks *bb, sector_t s, int sectors,
 int badblocks_check(struct badblocks *bb, sector_t s, int sectors,
 			sector_t *first_bad, int *bad_sectors)
 {
-	return _badblocks_check(bb, s, sectors, first_bad, bad_sectors);
+	unsigned int seq;
+	int rv;
+
+	WARN_ON(bb->shift < 0 || sectors == 0);
+
+	if (bb->shift > 0) {
+		/* round the start down, and the end up */
+		sector_t target = s + sectors;
+
+		rounddown(s, 1 << bb->shift);
+		roundup(target, 1 << bb->shift);
+		sectors = target - s;
+	}
+
+retry:
+	seq = read_seqbegin(&bb->lock);
+	rv = _badblocks_check(bb, s, sectors, first_bad, bad_sectors);
+	if (read_seqretry(&bb->lock, seq))
+		goto retry;
+
+	return rv;
 }
 EXPORT_SYMBOL_GPL(badblocks_check);