md/raid1: Fix data corruption for degraded array with slow disk

read_balance() will avoid reading from slow disks as much as possible,
however, if valid data only lands in slow disks, and a new normal disk
is still in recovery, unrecovered data can be read:

raid1_read_request
 read_balance
  raid1_should_read_first
  -> return false
  choose_best_rdev
  -> normal disk is not recovered, return -1
  choose_bb_rdev
  -> missing the checking of recovery, return the normal disk
 -> read unrecovered data

Root cause is that the checking of recovery is missing in
choose_bb_rdev(). Hence add such checking to fix the problem.

Also fix similar problem in choose_slow_rdev().

Cc: [email protected]
Fixes: 9f3ced7 ("md/raid1: factor out choose_bb_rdev() from read_balance()")
Fixes: dfa8ecd ("md/raid1: factor out choose_slow_rdev() from read_balance()")
Reported-and-tested-by: Mateusz Jończyk <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Yu Kuai <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Song Liu <[email protected]>

drivers/md/raid1.c

@@ -617,6 +617,12 @@ static int choose_first_rdev(struct r1conf *conf, struct r1bio *r1_bio,
 	return -1;
 }
 
+static bool rdev_in_recovery(struct md_rdev *rdev, struct r1bio *r1_bio)
+{
+	return !test_bit(In_sync, &rdev->flags) &&
+	       rdev->recovery_offset < r1_bio->sector + r1_bio->sectors;
+}
+
 static int choose_bb_rdev(struct r1conf *conf, struct r1bio *r1_bio,
 			  int *max_sectors)
 {
@@ -635,6 +641,7 @@ static int choose_bb_rdev(struct r1conf *conf, struct r1bio *r1_bio,
 
 		rdev = conf->mirrors[disk].rdev;
 		if (!rdev || test_bit(Faulty, &rdev->flags) ||
+		    rdev_in_recovery(rdev, r1_bio) ||
 		    test_bit(WriteMostly, &rdev->flags))
 			continue;
 
@@ -673,7 +680,8 @@ static int choose_slow_rdev(struct r1conf *conf, struct r1bio *r1_bio,
 
 		rdev = conf->mirrors[disk].rdev;
 		if (!rdev || test_bit(Faulty, &rdev->flags) ||
-		    !test_bit(WriteMostly, &rdev->flags))
+		    !test_bit(WriteMostly, &rdev->flags) ||
+		    rdev_in_recovery(rdev, r1_bio))
 			continue;
 
 		/* there are no bad blocks, we can use this disk */
@@ -733,9 +741,7 @@ static bool rdev_readable(struct md_rdev *rdev, struct r1bio *r1_bio)
 	if (!rdev || test_bit(Faulty, &rdev->flags))
 		return false;
 
-	/* still in recovery */
-	if (!test_bit(In_sync, &rdev->flags) &&
-	    rdev->recovery_offset < r1_bio->sector + r1_bio->sectors)
+	if (rdev_in_recovery(rdev, r1_bio))
 		return false;
 
 	/* don't read from slow disk unless have to */