Re: Issues with md raid 1 on kernel 6.18 after booting kernel 6.19rc1 once

[BugReports <bugreports61@gmail.com>]

Hi,

ok, so no easy way back for me to the original state sadly.

The patch for 6.18 here: 
https://lore.kernel.org/stable/20251217130513.2706844-1-linan666@huaweicloud.com/T/#u

has the following in:

+ memcmp(sb->pad3, sb->pad3+1, sizeof(sb->pad3) - sizeof(sb->pad3[1]))) 
{ + pr_warn("Some padding is non-zero on %pg, might be a new feature\n", 
+ rdev->bdev); + if (check_new_feature) + return -EINVAL; + 
pr_warn("check_new_feature is disabled, data corruption possible\n"); + }

Data corruption (especially the one happening in the background without 
noticing) would be the worst case.

So is it really safe to use that patch+module option with my modified md 
raid  on kernel 6.18 (can easily apply the patch on my 6.18 kernel) ?

Br

Am 18.12.25 um 15:54 schrieb Li Nan:
>
>
> 在 2025/12/18 18:41, Bugreports61 写道:
>> Hi,
>>
>>
>> reading the threads it was now decided that only newly created arrays 
>> will get the lbs adjustment and patches to make it work on older 
>> kernels will not happen:
>>
>>
>> How do i get back my md raid1 to a state which makes it usable again 
>> on older kernels ?
>>
>> Is it  safe to simply mdadm --create --assume-clean /dev/mdX /sdX 
>> /sdY on kernel 6.18 to get the old superblock 1.2 information back 
>> without loosing data ?
>>
>>
>> My thx !
>>
>
> In principle, this works but remains a high-risk operation. I still
> recommend backporting this patch and add module parameters to mitigate 
> the
> risk.
>
> https://lore.kernel.org/stable/20251217130513.2706844-1-linan666@huaweicloud.com/T/#u 
>
>
> This issue will be fixed upstream soon. The patch is under validation and
> expected to be submitted tomorrow. However, the existing impact cannot be
> undone – apologies for this.
>