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Subject: Re: 4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with
 virtio-blk (also 4.12 stable)
From:   Jens Axboe <axboe@kernel.dk>
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>
References: <9c5eec5d-f542-4d76-6933-6fe31203ce09@de.ibm.com>
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 <823b9dd5-7781-5a72-03ff-bc931433fc19@kernel.dk>
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Message-ID: <055f040d-3f9a-a8fd-e8e2-326c6b9094a1@kernel.dk>
Date:   Tue, 21 Nov 2017 11:09:33 -0700
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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.

-- 
Jens Axboe


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