linux-kernel - Re: blk-mq crash under KVM in multiqueue block code (with virtio-blk and ext4)

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Message-ID: <5419EC19.9050100@kernel.dk>
Date:	Wed, 17 Sep 2014 14:16:25 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	Ming Lei <tom.leiming@...il.com>
CC:	Christian Borntraeger <borntraeger@...ibm.com>,
	rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org >> Linux Kernel Mailing List" 
	<linux-kernel@...r.kernel.org>
Subject: Re: blk-mq crash under KVM in multiqueue block code (with virtio-blk
 and ext4)

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

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