On 5/16/21 4:42 PM, Matthias Ferdinand wrote:
> On Sat, May 15, 2021 at 09:06:07PM +0200, Thorsten Knabe wrote:
>> Hello.
>>
>> Starting with Linux 5.12 bcache triggers a BUG() after a few minutes of
>> usage.
>>
>> Linux up to 5.11.x is not affected by this bug.
>>
>> Environment:
>> - Debian 10 AMD 64
>> - Kernel 5.12 - 5.12.4
>> - Filesystem ext4
>> - Backing device: degraded software RAID-6 (MD) with 3 of 4 disks active
>>   (unsure if the degraded RAID-6 has an effect or not)
>> - Cache device: Single SSD
> 
> Sorry I can't immediately help with bcache, but for DRBD, there was a
> similar problem with DRBD on degraded md-raid fixed just recently:
> 
>     https://lists.linbit.com/pipermail/drbd-user/2021-May/025904.html
> 
> Although they had silent data corruption AFAICT, not a loud BUG(), and
> they stated problems started with kernel 4.3.
> 
> For DRBD it had to do with split BIOs and readahead, which degraded
> md-raid may or may not fail, and missing a fail on parts of a split-up
> readahead BIO.
> 
> Matthias
> 


This is caused by a hidden issue which is triggered by the bio code
change in v5.12.

The attached patch can help to avoid the panic, and the finally fixes
are under testing and will be posted very soon.

Coly Li