Re: Bad raid0 bio too large problem

[Neil Brown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 3060 bytes --]

Jes Sorensen <Jes.Sorensen@redhat.com> writes:

> Neil Brown <neilb@suse.de> 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.
>>
>> Well that's pretty convincing - thanks.
>> And as you say - it is tagged for -stable so really needs to be fixed.
>>
>> Stares at the code again.  And again.
>>
>> Ahhh.  that patch moved the
>>   blk_queue_max_hw_sectors(mddev->queue, mddev->chunk_sectors);
>> to after
>>  disk_stack_limits(...);
>>
>> That is wrong.
>>
>> Could you confirm that this fixes your test?
>
> I refuse to do that! .... since Xiao beat me to it! Thanks!
>
> I was half way bisecting my way through it last night. For some reason
> the problem was reproducible in 4.2 if I applied the offending patch,
> but not in 4.3-rc2.
>
> Any chance you'll push these to your git tree in the near future?

Pushed.
Thanks,
NeilBrown

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 818 bytes --]