Re: Bad raid0 bio too large problem

[Jes Sorensen <Jes.Sorensen@redhat.com>]

Neil Brown <neilb@suse.de> writes:
> Jes Sorensen <Jes.Sorensen@redhat.com> writes:
>
>> Hi Neil,
>>
>> I think we have some bad side effects with this patch:
>>
>> commit 199dc6ed5179251fa6158a461499c24bdd99c836
>> Author: NeilBrown <neilb@suse.com>
>> Date:   Mon Aug 3 13:11:47 2015 +1000
>>
>>     md/raid0: update queue parameter in a safer location.
>>     
>>     When a (e.g.) RAID5 array is reshaped to RAID0, the updating
>>     of queue parameters (e.g. max number of sectors per bio) is
>>     done in the wrong place.
>>     It should be part of ->run, but it is actually part of ->takeover.
>>     This means it happens before level_store() calls:
>>     
>>         blk_set_stacking_limits(&mddev->queue->limits);
>>     
>> Running the '03r0assem' test suite fills my kernel log with output like
>> below. Yi Zhang also had issues where writes failed too.
>>
>> robably something we need to resolve for 4.2-final or revert the
>> offending patch.
>>
>> Cheers,
>> Jes
>>
>> md: bind<loop0>
>> md: bind<loop1>
>> md: bind<loop2>
>> md/raid0:md2: md_size is 116736 sectors.
>> md: RAID0 configuration for md2 - 1 zone
>> md: zone0=[loop0/loop1/loop2]
>>       zone-offset=         0KB, device-offset=         0KB, size=     58368KB
>>
>> md2: detected capacity change from 0 to 59768832
>> bio too big device loop0 (296 > 255)
>> bio too big device loop0 (272 > 255)
>
> 1/ Why do you blame that particular patch?
>
> 2/ Where is that error message coming from?  I cannot find "bio too big"
>   in the kernel (except in a comment).
>   Commit: 54efd50bfd87 ("block: make generic_make_request handle
> arbitrarily sized bios")
>   removed the only instance of the error message that I know of.
>
> Which kernel exactly are you testing?

I blame it because of bisect - I revert that patch and the issue goes
away.

I checked out 199dc6ed5179251fa6158a461499c24bdd99c836 in Linus' tree,
see the bio too large. I revert it and it goes away.

Cheers,
Jes