linux-kernel - Re: [PATCH] md: zero the original position of sb for 0.90 and 1.0

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Date:   Thu, 17 May 2018 09:21:28 -0700
From:   Shaohua Li <shli@...nel.org>
To:     Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     robert.butera@...cle.com, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] md: zero the original position of sb for 0.90 and 1.0

On Wed, May 16, 2018 at 05:18:39PM +0800, Jianchao Wang wrote:
> For sb version 0.90 and 1.0 which locates after data, when we increase
> the spindle volume size and grow the raid arry size, the older sb which is
> different between spindles will be left there. Due to this left sb, the
> spindle volume cannot be grown with zero filled part with  --asume-clean.
> applications have to take some workarounds such as sync_min/max to avoid
> resync.
> 
> It is easy and convevient for md to zero the older sb position after
> write sb to new position, so do it here.

>From the description, this looks easy to do in userspace, eg, you can zero the
super before increase the spindle volume. Convenience isn't a reason we should
put these code into kernel space.

Thanks,
Shaohua 
> Cc: robert.butera@...cle.com
> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
> ---
>  drivers/md/md.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index c208c01..a042add 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -1020,6 +1020,23 @@ int md_check_no_bitmap(struct mddev *mddev)
>  }
>  EXPORT_SYMBOL(md_check_no_bitmap);
>  
> +static void md_zero_original_sb_position(struct md_rdev *rdev, sector_t old_pos)
> +{
> +	struct page *zero_pg;
> +
> +	zero_pg = alloc_pages(GFP_KERNEL | __GFP_ZERO, 0);
> +	if (!zero_pg) {
> +		pr_warn("%s: failed to get page for zero original sb position",
> +				mdname(rdev->mddev));
> +		return;
> +	}
> +	md_super_write(rdev->mddev, rdev, old_pos, rdev->sb_size,
> +		       zero_pg);
> +	wait_event(rdev->mddev->sb_wait,
> +			(atomic_read(&rdev->mddev->pending_writes) == 0));
> +	__free_pages(zero_pg, 0);
> +}
> +
>  /*
>   * load_super for 0.90.0
>   */
> @@ -1394,6 +1411,8 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
>  static unsigned long long
>  super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>  {
> +	sector_t old_pos = rdev->sb_start;
> +
>  	if (num_sectors && num_sectors < rdev->mddev->dev_sectors)
>  		return 0; /* component must fit device */
>  	if (rdev->mddev->bitmap_info.offset)
> @@ -1411,6 +1430,8 @@ super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>  		md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
>  		       rdev->sb_page);
>  	} while (md_super_wait(rdev->mddev) < 0);
> +
> +	md_zero_original_sb_position(rdev, old_pos);
>  	return num_sectors;
>  }
>  
> @@ -1953,6 +1974,8 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>  {
>  	struct mdp_superblock_1 *sb;
>  	sector_t max_sectors;
> +	sector_t old_pos = 0;
> +
>  	if (num_sectors && num_sectors < rdev->mddev->dev_sectors)
>  		return 0; /* component must fit device */
>  	if (rdev->data_offset != rdev->new_data_offset)
> @@ -1969,6 +1992,7 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>  	} else {
>  		/* minor version 0; superblock after data */
>  		sector_t sb_start;
> +		old_pos = rdev->sb_start;
>  		sb_start = (i_size_read(rdev->bdev->bd_inode) >> 9) - 8*2;
>  		sb_start &= ~(sector_t)(4*2 - 1);
>  		max_sectors = rdev->sectors + sb_start - rdev->sb_start;
> @@ -1984,6 +2008,9 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>  		md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
>  			       rdev->sb_page);
>  	} while (md_super_wait(rdev->mddev) < 0);
> +
> +	if (old_pos)
> +		md_zero_original_sb_position(rdev, old_pos);
>  	return num_sectors;
>  
>  }
> -- 
> 2.7.4
>