[dm-devel] [PATCH 1/2] md/raid0: Introduce new array state 'broken' for raid0

[Song Liu]

On Mon, Jul 29, 2019 at 1:33 PM Guilherme G. Piccoli
<gpiccoli at canonical.com> wrote:
>
> Currently if a md/raid0 array gets one or more members removed while
> being mounted, kernel keeps showing state 'clean' in the 'array_state'
> sysfs attribute. Despite udev signaling the member device is gone, 'mdadm'
> cannot issue the STOP_ARRAY ioctl successfully, given the array is mounted.
>
> Nothing else hints that something is wrong (except that the removed devices
> don't show properly in the output of 'mdadm detail' command). There is no
> other property to be checked, and if user is not performing reads/writes
> to the array, even kernel log is quiet and doesn't give a clue about the
> missing member.
>
> This patch changes this behavior; when 'array_state' is read we introduce
> a non-expensive check (only for raid0) that relies in the comparison of
> the total number of disks when array was assembled with gendisk flags of
> those devices to validate if all members are available and functional.
> A new array state 'broken' was added: it mimics the state 'clean' in every
> aspect, being useful only to distinguish if such array has some member
> missing. Also, we show a rate-limited warning in kernel log in such case.
>
> This patch has no proper functional change other than adding a 'clean'-like
> state; it was tested with ext4 and xfs filesystems. It requires a 'mdadm'
> counterpart to handle the 'broken' state.
>
> Cc: NeilBrown <neilb at suse.com>
> Cc: Song Liu <songliubraving at fb.com>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli at canonical.com>
> ---
>
[...]
> @@ -4315,6 +4329,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
>                 break;
>         case write_pending:
>         case active_idle:
> +       case broken:
>                 /* these cannot be set */
>                 break;
>         }

Maybe it is useful to set "broken" state? When user space found some issues
with the drive?

Thanks,
Song


> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 41552e615c4c..e7b42b75701a 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -590,6 +590,8 @@ struct md_personality
>         int (*congested)(struct mddev *mddev, int bits);
>         /* Changes the consistency policy of an active array. */
>         int (*change_consistency_policy)(struct mddev *mddev, const char *buf);
> +       /* Check if there is any missing/failed members - RAID0 only for now. */
> +       bool (*is_missing_dev)(struct mddev *mddev);
>  };
>
>  struct md_sysfs_entry {
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 58a9cc5193bf..79618a6ae31a 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -455,6 +455,31 @@ static inline int is_io_in_chunk_boundary(struct mddev *mddev,
>         }
>  }
>
> +bool raid0_is_missing_dev(struct mddev *mddev)
> +{
> +       struct md_rdev *rdev;
> +       static int already_missing;
> +       int def_disks, work_disks = 0;
> +       struct r0conf *conf = mddev->private;
> +
> +       def_disks = conf->strip_zone[0].nb_dev;
> +       rdev_for_each(rdev, mddev)
> +               if (rdev->bdev->bd_disk->flags & GENHD_FL_UP)
> +                       work_disks++;
> +
> +       if (unlikely(def_disks - work_disks)) {
> +               if (!already_missing) {
> +                       already_missing = 1;
> +                       pr_warn("md: %s: raid0 array has %d missing/failed members\n",
> +                               mdname(mddev), (def_disks - work_disks));
> +               }
> +               return true;
> +       }
> +
> +       already_missing = 0;
> +       return false;
> +}
> +
>  static void raid0_handle_discard(struct mddev *mddev, struct bio *bio)
>  {
>         struct r0conf *conf = mddev->private;
> @@ -789,6 +814,7 @@ static struct md_personality raid0_personality=
>         .takeover       = raid0_takeover,
>         .quiesce        = raid0_quiesce,
>         .congested      = raid0_congested,
> +       .is_missing_dev = raid0_is_missing_dev,
>  };
>
>  static int __init raid0_init (void)
> --
> 2.22.0
>