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

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Date:	Wed, 17 Sep 2014 23:24:37 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	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 Wed, Sep 17, 2014 at 10:22 PM, Jens Axboe <axboe@...nel.dk> wrote:
>
> Another way would be to ensure that the timeout handler doesn't touch hw_ctx
> or tag_sets that aren't fully initialized yet. But I think this is
> safer/cleaner.

That may not be easy or enough to check if hw_ctx/tag_sets are
fully initialized if you mean all requests have been used one time.

On Wed, Sep 17, 2014 at 10:11 PM, David Hildenbrand
> I was playing with a simple patch that just sets cmd_flags and action_flags to

What is action_flags?

> 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.


Thanks,
-- 
Ming Lei
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