Re: [PATCH v4] super1: fix sb->max_dev when adding a new disk in linear array

[NeilBrown <neilb@suse.com>]

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On Mon, May 22 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 | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/super1.c b/super1.c
> index 2fcb814..03cea72 100644
> --- a/super1.c
> +++ b/super1.c
> @@ -1267,8 +1267,10 @@ 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 >= max) {
> +			sb->dev_roles[max] = __cpu_to_le16(MD_DISK_ROLE_SPARE);

Why do you assign to dev_roles[max]?
max must equal i here, and a few lines later:
		sb->dev_roles[i] = __cpu_to_le16(info->disk.raid_disk);

your assignment is over-written.  So it is pointless.
If i was greater than max (which should be impossible), you assignment
here would corrupt the dev_roles table.

Please drop this assignment.

>  			sb->max_dev = __cpu_to_le32(max+1);
> +		}
>  
>  		random_uuid(sb->device_uuid);
>  
> @@ -1293,9 +1295,14 @@ static int update_super1(struct supertype *st, struct mdinfo *info,
>  			}
>  		}
>  	} else if (strcmp(update, "linear-grow-update") == 0) {
> +		unsigned int max = __le32_to_cpu(sb->max_dev);
>  		sb->raid_disks = __cpu_to_le32(info->array.raid_disks);
>  		sb->dev_roles[info->disk.number] =
>  			__cpu_to_le16(info->disk.raid_disk);
> +		if (info->array.raid_disks >= max) {

if raid_disks == max there is no need to change anything.
It is only when raid_disks > max that you need to increase max.

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

When you increase max, you do need to assign MD_DISK_ROLE_SPARE to the
new element, but you need to do that *before* disk.raid_disk is
assigned, in case info->disk.number == max (as it could be for the
recently added device).

NeilBrown


> +			sb->max_dev = __cpu_to_le32(max+1);
> +		}
>  	} else if (strcmp(update, "resync") == 0) {
>  		/* make sure resync happens */
>  		sb->resync_offset = 0ULL;
> -- 
> 2.12.0

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