Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: 4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with
 virtio-blk (also 4.12 stable)
To:     Christian Borntraeger <borntraeger@de.ibm.com>,
        Bart Van Assche <Bart.VanAssche@wdc.com>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "mst@redhat.com" <mst@redhat.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org
References: <9c5eec5d-f542-4d76-6933-6fe31203ce09@de.ibm.com>
 <5c9f2228-0a8b-8225-7038-e6cb3f31ca0b@kernel.dk>
 <2e44dbd3-2f90-c267-560c-91d1d4b0e892@de.ibm.com>
 <823b9dd5-7781-5a72-03ff-bc931433fc19@kernel.dk>
 <bd928410-4d38-603e-00c9-4c4db20d8e86@de.ibm.com>
 <15f232d2-2aaa-df7c-57e8-2f710e051e84@de.ibm.com>
 <c8bd769e-9742-205d-11b0-469428a8579c@de.ibm.com>
 <b7b3cf4b-837e-f9ba-61c0-4f9ddd8b9a95@kernel.dk>
 <055f040d-3f9a-a8fd-e8e2-326c6b9094a1@kernel.dk>
 <1aeecf2e-a68e-4c18-5912-2473f457e6ea@de.ibm.com>
 <8fedc2ad-d775-7789-742c-92ca928a3aee@kernel.dk>
 <ebf96f76-3f53-283d-042d-8ea3f5eddb3d@kernel.dk>
 <ba994ec6-8db6-f77e-ac73-92e3f6b0135a@de.ibm.com>
 <ae02b9c5-9a2e-cb8b-7828-475b3c0b1cb9@kernel.dk>
 <c438db5f-f4f1-69f8-37f3-e91eae29fa25@de.ibm.com>
 <d8dbde03-f528-1cac-03dd-bcc724fcd5c8@kernel.dk>
 <276625a9-44fb-719d-9281-caacefdbb99f@de.ibm.com>
 <eceae481-cf9a-0429-7a15-c363a8e7bc2a@kernel.dk>
 <1ddd1cd4-2862-849e-7849-82544bcb86be@de.ibm.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <08e6f35a-4f49-973e-99f7-6087b44337c4@kernel.dk>
Date:   Tue, 21 Nov 2017 13:39:11 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.4.0
MIME-Version: 1.0
In-Reply-To: <1ddd1cd4-2862-849e-7849-82544bcb86be@de.ibm.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 11/21/2017 01:31 PM, Christian Borntraeger wrote:
> 
> 
> On 11/21/2017 09:21 PM, Jens Axboe wrote:
>> On 11/21/2017 01:19 PM, Christian Borntraeger wrote:
>>>
>>> On 11/21/2017 09:14 PM, Jens Axboe wrote:
>>>> On 11/21/2017 01:12 PM, Christian Borntraeger wrote:
>>>>>
>>>>>
>>>>> On 11/21/2017 08:30 PM, Jens Axboe wrote:
>>>>>> On 11/21/2017 12:15 PM, Christian Borntraeger wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 11/21/2017 07:39 PM, Jens Axboe wrote:
>>>>>>>> On 11/21/2017 11:27 AM, Jens Axboe wrote:
>>>>>>>>> On 11/21/2017 11:12 AM, Christian Borntraeger wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 11/21/2017 07:09 PM, Jens Axboe wrote:
>>>>>>>>>>> On 11/21/2017 10:27 AM, Jens Axboe wrote:
>>>>>>>>>>>> On 11/21/2017 03:14 AM, Christian Borntraeger wrote:
>>>>>>>>>>>>> Bisect points to
>>>>>>>>>>>>>
>>>>>>>>>>>>> 1b5a7455d345b223d3a4658a9e5fce985b7998c1 is the first bad commit
>>>>>>>>>>>>> commit 1b5a7455d345b223d3a4658a9e5fce985b7998c1
>>>>>>>>>>>>> Author: Christoph Hellwig <hch@lst.de>
>>>>>>>>>>>>> Date:   Mon Jun 26 12:20:57 2017 +0200
>>>>>>>>>>>>>
>>>>>>>>>>>>>     blk-mq: Create hctx for each present CPU
>>>>>>>>>>>>>     
>>>>>>>>>>>>>     commit 4b855ad37194f7bdbb200ce7a1c7051fecb56a08 upstream.
>>>>>>>>>>>>>     
>>>>>>>>>>>>>     Currently we only create hctx for online CPUs, which can lead to a lot
>>>>>>>>>>>>>     of churn due to frequent soft offline / online operations.  Instead
>>>>>>>>>>>>>     allocate one for each present CPU to avoid this and dramatically simplify
>>>>>>>>>>>>>     the code.
>>>>>>>>>>>>>     
>>>>>>>>>>>>>     Signed-off-by: Christoph Hellwig <hch@lst.de>
>>>>>>>>>>>>>     Reviewed-by: Jens Axboe <axboe@kernel.dk>
>>>>>>>>>>>>>     Cc: Keith Busch <keith.busch@intel.com>
>>>>>>>>>>>>>     Cc: linux-block@vger.kernel.org
>>>>>>>>>>>>>     Cc: linux-nvme@lists.infradead.org
>>>>>>>>>>>>>     Link: http://lkml.kernel.org/r/20170626102058.10200-3-hch@lst.de
>>>>>>>>>>>>>     Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>>>>>>>>>>>>>     Cc: Oleksandr Natalenko <oleksandr@natalenko.name>
>>>>>>>>>>>>>     Cc: Mike Galbraith <efault@gmx.de>
>>>>>>>>>>>>>     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>>>>>>>>>>
>>>>>>>>>>>> I wonder if we're simply not getting the masks updated correctly. I'll
>>>>>>>>>>>> take a look.
>>>>>>>>>>>
>>>>>>>>>>> Can't make it trigger here. We do init for each present CPU, which means
>>>>>>>>>>> that if I offline a few CPUs here and register a queue, those still show
>>>>>>>>>>> up as present (just offline) and get mapped accordingly.
>>>>>>>>>>>
>>>>>>>>>>> From the looks of it, your setup is different. If the CPU doesn't show
>>>>>>>>>>> up as present and it gets hotplugged, then I can see how this condition
>>>>>>>>>>> would trigger. What environment are you running this in? We might have
>>>>>>>>>>> to re-introduce the cpu hotplug notifier, right now we just monitor
>>>>>>>>>>> for a dead cpu and handle that.
>>>>>>>>>>
>>>>>>>>>> I am not doing a hot unplug and the replug, I use KVM and add a previously
>>>>>>>>>> not available CPU.
>>>>>>>>>>
>>>>>>>>>> in libvirt/virsh speak:
>>>>>>>>>>   <vcpu placement='static' current='1'>4</vcpu>
>>>>>>>>>
>>>>>>>>> So that's why we run into problems. It's not present when we load the device,
>>>>>>>>> but becomes present and online afterwards.
>>>>>>>>>
>>>>>>>>> Christoph, we used to handle this just fine, your patch broke it.
>>>>>>>>>
>>>>>>>>> I'll see if I can come up with an appropriate fix.
>>>>>>>>
>>>>>>>> Can you try the below?
>>>>>>>
>>>>>>>
>>>>>>> It does prevent the crash but it seems that the new CPU is not "used " after the hotplug for mq:
>>>>>>>
>>>>>>>
>>>>>>> output with 2 cpus:
>>>>>>> /sys/kernel/debug/block/vda
>>>>>>> /sys/kernel/debug/block/vda/hctx0
>>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0
>>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/completed
>>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/merged
>>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/dispatched
>>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/rq_list
>>>>>>> /sys/kernel/debug/block/vda/hctx0/active
>>>>>>> /sys/kernel/debug/block/vda/hctx0/run
>>>>>>> /sys/kernel/debug/block/vda/hctx0/queued
>>>>>>> /sys/kernel/debug/block/vda/hctx0/dispatched
>>>>>>> /sys/kernel/debug/block/vda/hctx0/io_poll
>>>>>>> /sys/kernel/debug/block/vda/hctx0/sched_tags_bitmap
>>>>>>> /sys/kernel/debug/block/vda/hctx0/sched_tags
>>>>>>> /sys/kernel/debug/block/vda/hctx0/tags_bitmap
>>>>>>> /sys/kernel/debug/block/vda/hctx0/tags
>>>>>>> /sys/kernel/debug/block/vda/hctx0/ctx_map
>>>>>>> /sys/kernel/debug/block/vda/hctx0/busy
>>>>>>> /sys/kernel/debug/block/vda/hctx0/dispatch
>>>>>>> /sys/kernel/debug/block/vda/hctx0/flags
>>>>>>> /sys/kernel/debug/block/vda/hctx0/state
>>>>>>> /sys/kernel/debug/block/vda/sched
>>>>>>> /sys/kernel/debug/block/vda/sched/dispatch
>>>>>>> /sys/kernel/debug/block/vda/sched/starved
>>>>>>> /sys/kernel/debug/block/vda/sched/batching
>>>>>>> /sys/kernel/debug/block/vda/sched/write_next_rq
>>>>>>> /sys/kernel/debug/block/vda/sched/write_fifo_list
>>>>>>> /sys/kernel/debug/block/vda/sched/read_next_rq
>>>>>>> /sys/kernel/debug/block/vda/sched/read_fifo_list
>>>>>>> /sys/kernel/debug/block/vda/write_hints
>>>>>>> /sys/kernel/debug/block/vda/state
>>>>>>> /sys/kernel/debug/block/vda/requeue_list
>>>>>>> /sys/kernel/debug/block/vda/poll_stat
>>>>>>
>>>>>> Try this, basically just a revert.
>>>>>
>>>>> Yes, seems to work.
>>>>>
>>>>> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>>
>>>> Great, thanks for testing.
>>>>
>>>>> Do you know why the original commit made it into 4.12 stable? After all
>>>>> it has no Fixes tag and no cc stable-
>>>>
>>>> I was wondering the same thing when you said it was in 4.12.stable and
>>>> not in 4.12 release. That patch should absolutely not have gone into
>>>> stable, it's not marked as such and it's not fixing a problem that is
>>>> stable worthy. In fact, it's causing a regression...
>>>>
>>>> Greg? Upstream commit is mentioned higher up, start of the email.
>>>>
>>>
>>>
>>> Forgot to cc Greg?
>>
>> I did, thanks for doing that. Now I wonder how to mark this patch,
>> as we should revert it from kernels that have the bad commit. 4.12
>> is fine, 4.12.later-stable is not.
>>
> 
> I think we should tag it with:
> 
> Fixes: 4b855ad37194 ("blk-mq: Create hctx for each present CPU")
> 
> which should bring it into 4.13 stable and 4.14 stable. 4.12 stable seems EOL anyway.

Yeah, I think so too. But thinking more about this, I'm pretty sure this
adds a bad lock dependency with hotplug. Need to verify so we ensure we
don't introduce a potential deadlock here...

-- 
Jens Axboe


From 1584709185437162577@xxx Tue Nov 21 20:34:09 +0000 2017
X-GM-THRID: 1584670276912512570
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread