Re: [PATCH] super1: fix sb->max_dev when adding a new disk in linear array

[NeilBrown <neilb@suse.com>]

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On Tue, May 16 2017, Lidong Zhong wrote:

> The value of sb->max_dev will always be increased by 1 when adding
> a new disk in linear array. It causes an inconsistence between each
> disk in the array and the "Array State" value of "mdadm --examine DISK"
> is wrong. For example, when adding the first new disk into linear array
> it will be:
>
> Array State : RAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> ('A' == active, '.' == missing, 'R' == replacing)
>
> Adding the second disk into linear array it will be
>
> Array State : .AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> ('A' == active, '.' == missing, 'R' == replacing)
>
> Signed-off-by: Lidong Zhong <lzhong@suse.com>
> ---
>  super1.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/super1.c b/super1.c
> index 87a74cb..3d49bee 100644
> --- a/super1.c
> +++ b/super1.c
> @@ -1184,8 +1184,10 @@ static int update_super1(struct supertype *st, struct mdinfo *info,
>  				break;
>  		sb->dev_number = __cpu_to_le32(i);
>  		info->disk.number = i;
> -		if (max >= __le32_to_cpu(sb->max_dev))
> +		if (i >= __le32_to_cpu(sb->max_dev)) {

This change is correct - thanks.  Though
    if (i >= max) {

might be clearer and simpler.


>  			sb->max_dev = __cpu_to_le32(max+1);
> +			sb->dev_roles[sb->max_dev] = __cpu_to_le16(MD_DISK_ROLE_SPARE);

This change is wrong.
At the very least, the dev_roles[] array needs to be indexed by a
host-order number, not a little-endian number.
But the change is not needed because dev_roles[max_dev] is never used.
See role_from_sb().
dev_rols[max_dev - 1] does need to be set, but the line

		sb->dev_roles[i] = __cpu_to_le16(info->disk.raid_disk);

almost certainly does that.
It might be better to do
  if (i >= max) {
     while (max <= i) {
        sb->dev_roles[max] = __cpu_to_le16(MD_DISK_ROLE_SPARE);
        max += 1;
     }
     sb->max_dev = __cpu_to_le32(max);
  }

> +		}
>  
>  		random_uuid(sb->device_uuid);
>  
> @@ -1214,6 +1216,10 @@ static int update_super1(struct supertype *st, struct mdinfo *info,
>  		sb->raid_disks = __cpu_to_le32(info->array.raid_disks);
>  		sb->dev_roles[info->disk.number] =
>  			__cpu_to_le16(info->disk.raid_disk);
> +		if (sb->raid_disks+1 >= __le32_to_cpu(sb->max_dev)) {
> +			sb->max_dev = __cpu_to_le32(sb->raid_disks+1);
> +			sb->dev_roles[sb->max_dev] = __cpu_to_le16(MD_DISK_ROLE_SPARE);

Again, max_dev is little-endian, so cannot be used as an index.
And I think you are updating the wrong element in the dev_roles array.

Thanks,
NeilBrown


> +		}
>  	} else if (strcmp(update, "resync") == 0) {
>  		/* make sure resync happens */
>  		sb->resync_offset = 0ULL;
> -- 
> 2.12.0

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