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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Mike Snitzer <snitzer@redhat.com>
Cc:     axboe@kernel.dk, linuxppc-dev@lists.ozlabs.org,
        satheera@in.ibm.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: System not booting since dm changes? (was Linux 4.20-rc1)
In-Reply-To: <20181105135157.GA11485@redhat.com>
References: <CAHk-=whDiwASMgw8Q7TNA2MJhf3s=ouK4+_3ioqmobs-yagnkQ@mail.gmail.com> <87tvkvddnk.fsf@concordia.ellerman.id.au> <20181105135157.GA11485@redhat.com>
Date:   Wed, 07 Nov 2018 11:59:20 +1100
Message-ID: <871s7xsnx3.fsf@concordia.ellerman.id.au>
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Sender: linux-kernel-owner@vger.kernel.org
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Mike Snitzer <snitzer@redhat.com> writes:
> On Mon, Nov 05 2018 at  5:25am -0500,
> Michael Ellerman <mpe@ellerman.id.au> wrote:
>
>> Linus Torvalds <torvalds@linux-foundation.org> writes:
>> ...
>> > Mike Snitzer (1):
>> >     device mapper updates
>> 
>> Hi Mike,
>> 
>> Replying here because I can't find the device-mapper pull or the patch
>> in question on LKML. I guess I should be subscribed to dm-devel.
>> 
>> We have a box that doesn't boot any more, bisect points at one of:
>> 
>>   cef6f55a9fb4 Mike Snitzer       dm table: require that request-based DM be layered on blk-mq devices 
>>   953923c09fe8 Mike Snitzer       dm: rename DM_TYPE_MQ_REQUEST_BASED to DM_TYPE_REQUEST_BASED 
>>   6a23e05c2fe3 Jens Axboe         dm: remove legacy request-based IO path 
>> 
>> 
>> It's a Power8 system running Rawhide, it does have multipath, but I'm
>> told it was setup by the Fedora installer, ie. nothing fancy.
>> 
>> The symptom is the system can't find its root filesystem and drops into
>> the initramfs shell. The dmesg includes a bunch of errors like below:
>> 
>>   [   43.263460] localhost multipathd[1344]: sdb: fail to get serial
>>   [   43.268762] localhost multipathd[1344]: mpatha: failed in domap for addition of new path sdb
>>   [   43.268762] localhost multipathd[1344]: uevent trigger error
>>   [   43.282065] localhost kernel: device-mapper: table: table load rejected: not all devices are blk-mq request-stackable
> ...
>>
>> Any ideas what's going wrong here?
>
> "table load rejected: not all devices are blk-mq request-stackable"
> speaks to the fact that you aren't using blk-mq for scsi (aka scsi-mq).
>
> You need to use scsi_mod.use_blk_mq=Y on the kernel commandline (or set
> CONFIG_SCSI_MQ_DEFAULT in your kernel config)

Thanks.

Looks like CONFIG_SCSI_MQ_DEFAULT is default y, so new configs should
pick that up by default. We must have had an old .config that didn't get
that update.

cheers