Re: [PATCH -next v3 7/7] md: delay remove_and_add_spares() for read only array to md_start_sync()

[Xiao Ni <xni@redhat.com>]

On Sun, Aug 20, 2023 at 5:13 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Before this patch, for read-only array:
>
> md_check_recovery() check that 'MD_RECOVERY_NEEDED' is set, then it will
> call remove_and_add_spares() directly to try to remove and add rdevs
> from array.
>
> After this patch:
>
> 1) md_check_recovery() check that 'MD_RECOVERY_NEEDED' is set, and the
>    worker 'sync_work' is not pending, and there are rdevs can be added
>    or removed, then it will queue new work md_start_sync();
> 2) md_start_sync() will call remove_and_add_spares() and exist;
>
> This change make sure that array reconfiguration is independent from
> daemon, and it'll be much easier to synchronize it with io, consier
> that io may rely on daemon thread to be done.
>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  drivers/md/md.c | 43 +++++++++++++++++++++++++++++++++----------
>  1 file changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index cdc361c521d4..f08b683f724f 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -4866,6 +4866,7 @@ action_store(struct mddev *mddev, const char *page, size_t len)
>                 /* A write to sync_action is enough to justify
>                  * canceling read-auto mode
>                  */
> +               flush_work(&mddev->sync_work);
>                 mddev->ro = MD_RDWR;
>                 md_wakeup_thread(mddev->sync_thread);
>         }
> @@ -7638,6 +7639,10 @@ static int md_ioctl(struct block_device *bdev, blk_mode_t mode,
>                 mutex_unlock(&mddev->open_mutex);
>                 sync_blockdev(bdev);
>         }
> +
> +       if (!md_is_rdwr(mddev))
> +               flush_work(&mddev->sync_work);
> +
>         err = mddev_lock(mddev);
>         if (err) {
>                 pr_debug("md: ioctl lock interrupted, reason %d, cmd %d\n",
> @@ -8562,6 +8567,7 @@ bool md_write_start(struct mddev *mddev, struct bio *bi)
>         BUG_ON(mddev->ro == MD_RDONLY);
>         if (mddev->ro == MD_AUTO_READ) {
>                 /* need to switch to read/write */
> +               flush_work(&mddev->sync_work);
>                 mddev->ro = MD_RDWR;
>                 set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
>                 md_wakeup_thread(mddev->thread);
> @@ -9191,6 +9197,16 @@ static bool rdev_addable(struct md_rdev *rdev)
>         return true;
>  }
>
> +static bool md_spares_need_change(struct mddev *mddev)
> +{
> +       struct md_rdev *rdev;
> +
> +       rdev_for_each(rdev, mddev)
> +               if (rdev_removeable(rdev) || rdev_addable(rdev))
> +                       return true;
> +       return false;
> +}
> +
>  static int remove_and_add_spares(struct mddev *mddev,
>                                  struct md_rdev *this)
>  {
> @@ -9311,6 +9327,12 @@ static void md_start_sync(struct work_struct *ws)
>
>         mddev_lock_nointr(mddev);
>
> +       if (!md_is_rdwr(mddev)) {
> +               remove_and_add_spares(mddev, NULL);
> +               mddev_unlock(mddev);
> +               return;
> +       }
> +
>         if (!md_choose_sync_action(mddev, &spares))
>                 goto not_running;
>
> @@ -9405,7 +9427,8 @@ void md_check_recovery(struct mddev *mddev)
>         }
>
>         if (!md_is_rdwr(mddev) &&
> -           !test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))
> +           (!test_bit(MD_RECOVERY_NEEDED, &mddev->recovery) ||
> +            work_pending(&mddev->sync_work)))
>                 return;
>         if ( ! (
>                 (mddev->sb_flags & ~ (1<<MD_SB_CHANGE_PENDING)) ||
> @@ -9433,15 +9456,8 @@ void md_check_recovery(struct mddev *mddev)
>                                  */
>                                 rdev_for_each(rdev, mddev)
>                                         clear_bit(Blocked, &rdev->flags);
> -                       /* On a read-only array we can:
> -                        * - remove failed devices
> -                        * - add already-in_sync devices if the array itself
> -                        *   is in-sync.
> -                        * As we only add devices that are already in-sync,
> -                        * we can activate the spares immediately.
> -                        */

Can we keep those comments?

> -                       remove_and_add_spares(mddev, NULL);
> -                       /* There is no thread, but we need to call
> +                       /*
> +                        * There is no thread, but we need to call
>                          * ->spare_active and clear saved_raid_disk
>                          */
>                         set_bit(MD_RECOVERY_INTR, &mddev->recovery);
> @@ -9449,6 +9465,13 @@ void md_check_recovery(struct mddev *mddev)
>                         clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
>                         clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
>                         clear_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags);
> +
> +                       /*
> +                        * Let md_start_sync() to remove and add rdevs to the
> +                        * array.
> +                        */
> +                       if (md_spares_need_change(mddev))
> +                               queue_work(md_misc_wq, &mddev->sync_work);
>                         goto unlock;
>                 }
>
> --
> 2.39.2
>

Reviewed-by: Xiao Ni <xni@redhat.com>