Re: linux-next: Boot hangs 3 minutes with device mapper on s390

[Steffen Maier <maier@linux.ibm.com>]

On 03/01/2019 07:30 PM, Mike Snitzer wrote:
> On Fri, Mar 01 2019 at 12:33pm -0500,
> Michael Holzheu <holzheu@linux.ibm.com> wrote:
> 
>> Hi Mike,
>>
>> On Fedora 29, the following "linux-next" commit introduced a regression on s390:
>>
>>    commit 1efa3bb79d3de8ca1b7f6770313a1fc0bebe25c7
>>    Author: Mike Snitzer <snitzer@redhat.com>
>>    Date:   Fri Feb 22 11:23:01 2019 -0500
>>
>>      dm: must allocate dm_noclone for stacked noclone devices
>>      
>>      Otherwise various lvm2 testsuite tests fail because the lower layers of
>>      the stacked noclone device aren't updated to allocate a new 'struct
>>      dm_clone' that reflects the upper layer bio that was issued to it.
>>      
>>      Fixes: 97a89458020b38 ("dm: improve noclone bio support")
>>      Reported-by: Mikulas Patocka <mpatocka@redhat.com>
>>      Signed-off-by: Mike Snitzer <snitzer@redhat.com>
>>
>> With this commit the boot hangs three minutes on a z/VM system with the
>> following device mapper setup:
>>
>> # dmsetup ls --tree
>> mpathe (252:5)
>>   ├─ (8:128)
>>   └─ (8:144)
>> mpathd (252:4)
>>   ├─ (8:96)
>>   └─ (8:112)
>> mpathc (252:3)
>>   ├─ (8:64)
>>   └─ (8:80)
>> mpathb (252:2)
>>   ├─ (8:32)
>>   └─ (8:48)
>> mpatha1 (252:1)
>>   └─mpatha (252:0)
>>      ├─ (8:16)
>>      └─ (8:0)
>>
>> On the console we get messages like the following:
>>
>>     10.116863 sd 3:0:0:1083719813: sdj Write Protect is off
>>     10.117170 sd 3:0:0:1083719813: sdj Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
>>     10.130562 sd 3:0:0:1083719813: sdj Attached SCSI disk
>>   A start job is running for udev Wai   Device Initialization (6s / 3min)
>>   A start job is running for udev Wai   Device Initialization (6s / 3min)
>>   A start job is running for udev Wai   Device Initialization (7s / 3min)
>>   A start job is running for udev Wai   Device Initialization (7s / 3min)
>>   A start job is running for udev Wai   Device Initialization (8s / 3min)
>>   ...
>>
>> After three minutes the boot process continues and the system comes.
>>
>> As kernel config we used "performance_defconfig" (make performance_defconfig).
> 
> I'm struggling to see why this particular change would cause such a boot
> stall -- but then resolve itself.
> 
> Can you provide the output from 'dmsetup table'?
> 
> Multipath defaults to blk-mq (request-based).  The change you've called
> into question is related to bio-based DM.  So There must be some
> bio-based DM layer ontop of the multipath devices.  Is mpatha1 a
> dm-linear device layered ontop of multipath?

Yes, mpatha1 is just an automatically generated kpartx linear partition 
mapping, so that one is bio-based.


-- 
Mit freundlichen Gruessen / Kind regards
Steffen Maier

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