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

[NeilBrown <neilb@suse.com>]

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On Fri, May 19 2017, Lidong Zhong wrote:

> On 05/19/2017 12:36 PM, NeilBrown wrote:
>> 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.
> Hi Neil,
>
> The reason I set all the dev_roles[0~max_dev-1] is because
> the following code
>
>   552     printf("   Array State : ");
>   553     for (d = 0; d < __le32_to_cpu(sb->raid_disks) + delta_extra; 
> d++) {
>   554         int cnt = 0;
>   555         unsigned int i;
>   556         for (i = 0; i < __le32_to_cpu(sb->max_dev); i++) {
>   557             unsigned int role = __le16_to_cpu(sb->dev_roles[i]); 
>
>   558             if (role == d) 
>
>   559                 cnt++; 
>
>   560         }

This code does not access dev_roles[max_dev], only up to
dev_roles[max_dev-1].
You changed dev_roles[max_dev], which will never be accessed.

>
>
>> 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);
>>   }
>>
>
>
> Thanks for the advice.
>
>>> +		}
>>>
>>>  		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.
>
> Yes, I didn't realized the valude is conversed to little-endian and the
> index is wrong too. Thank you for pointing this out. I will submit
> another version patch.

I look forward to it,
Thanks,
NeilBrown

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

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