From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jens Axboe <axboe@kernel.dk>
Subject: Re: blk-mq crash under KVM in multiqueue block code (with virtio-blk
	and ext4)
Date: Wed, 17 Sep 2014 14:16:25 -0600
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To: David Hildenbrand <dahi@linux.vnet.ibm.com>, Ming Lei <tom.leiming@gmail.com>
Cc: KVM list <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>, "linux-kernel@vger.kernel.org >> Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>, Virtualization List <virtualization@lists.linux-foundation.org>, Christian Borntraeger <borntraeger@de.ibm.com>
List-Id: virtualization@lists.linuxfoundation.org

On 09/17/2014 01:09 PM, David Hildenbrand wrote:
>>> 0. That should already be sufficient to hinder blk_mq_tag_to_rq and the calling
>>> method to do the wrong thing.
>>
>> Yes, clearing rq->cmd_flags should be enough.
>>
>> And looks better to move rq initialization to __blk_mq_free_request()
>> too, otherwise timeout still may see old cmd_flags and rq->q before
>> rq's new initialization.
> 
> Yes, __blk_mq_free_request() should also reset at least rq->cmd_flags, and I
> think we can remove the initialization from  __blk_mq_alloc_request().

And then we come full circle, that's how the code originally started out
(and it is the saner way to do things). So yes, I'd greatly applaud that.


-- 
Jens Axboe