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

Ming Lei
2014-09-17T15:24:37Z

On Wed, Sep 17, 2014 at 10:22 PM, Jens Axboe <axboe@kernel.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