Re: Bad raid0 bio too large problem

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

Jes Sorensen <Jes.Sorensen@redhat.com> writes:
> Jes Sorensen <Jes.Sorensen@redhat.com> writes:
>> 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.
>
> Hmmm Xiao tells me that the warning message is not in upstream, but I
> was sure I reproduced it in the upstream kernel as well. If I screwed
> up, my apologies, I am going back to my cave and will investigate
> further.

Digging a bit further, I was testing on a 4.2.0-rc5+ where I saw the
issue. That does raise the question of what this patch does to older
kernels, since it was submitted it for 2.6.35+.

"bio too big" message went away with this commit:

commit 54efd50bfd873e2dbf784e0b21a8027ba4299a3e
Author: Kent Overstreet <kent.overstreet@gmail.com>
Date:   Thu Apr 23 22:37:18 2015 -0700

    block: make generic_make_request handle arbitrarily sized bios

Cheers,
Jes