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

在 2025/12/19 0:04, BugReports 写道:
> 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/[email protected]/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

These dmesg note that using an array with new features in an old kernel may
cause data loss. If you configured LBS in a new kernel and use that array 
in an old kernel, data loss will occur due to LBS changes.

However, this problem does not exist if your RAID was created in an old
kernel, as LBS will not change when rolling back.

> 
> 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/[email protected]/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.
>>
> 
> .

-- 
Thanks,
Nan