[PATCH] md/raid5: correct degraded calculation in raid5_error

[bingjingc <bingjingc@synology.com>]

When disk failure occurs on new disks for reshape, mddev->degraded
is not calculated correctly. Faulty bit of the failure device is not
set before raid5_calc_degraded(conf).

mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/loop[012]
mdadm /dev/md0 -a /dev/loop3
mdadm /dev/md0 --grow -n4
mdadm /dev/md0 -f /dev/loop3 # simulating disk failure

cat /sys/block/md0/md/degraded # it outputs 0, but it should be 1.

However, mdadm -D /dev/md0 will show that it is degraded. It's a bug.
It can be fixed by moving the resources raid5_calc_degraded() depends
on before it.

Reported-by: Roy Chung <roychung@synology.com>
Reviewed-by: Alex Wu <alexwu@synology.com>
Signed-off-by: BingJing Chang <bingjingc@synology.com>
---
  drivers/md/raid5.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 31dc25e..98ce427 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2677,13 +2677,13 @@ static void raid5_error(struct mddev *mddev, 
struct md_rdev *rdev)
  	pr_debug("raid456: error called\n");

  	spin_lock_irqsave(&conf->device_lock, flags);
+	set_bit(Faulty, &rdev->flags);
  	clear_bit(In_sync, &rdev->flags);
  	mddev->degraded = raid5_calc_degraded(conf);
  	spin_unlock_irqrestore(&conf->device_lock, flags);
  	set_bit(MD_RECOVERY_INTR, &mddev->recovery);

  	set_bit(Blocked, &rdev->flags);
-	set_bit(Faulty, &rdev->flags);
  	set_mask_bits(&mddev->sb_flags, 0,
  		      BIT(MD_SB_CHANGE_DEVS) | BIT(MD_SB_CHANGE_PENDING));
  	pr_crit("md/raid:%s: Disk failure on %s, disabling device.\n"
--
2.7.4