[PATCH] nvme-fabrics: get ctrl reference in nvmf_dev_write

[Steve Wise]

> On Wed, 2016-07-13 at 04:18 +0200, Christoph Hellwig wrote:
> > On Tue, Jul 12, 2016 at 03:38:42PM -0700, Ming Lin wrote:
> > > From: Ming Lin <ming.l at samsung.com>
> > >
> > > Below crash was triggered when shutting down a nvme host node
> > > via 'reboot' that has 1 target device attached.
> > >
> > > That's because nvmf_dev_release() put the ctrl reference, but
> > > we didn't get the reference in nvmf_dev_write().
> > >
> > > So the ctrl was freed in nvme_rdma_free_ctrl() before
> > > nvme_rdma_free_ring()
> > > was called.
> >
> > The ->create_ctrl methods do a kref_init for the main refererence,
> > and a kref_get for the reference that nvmf_dev_release drops,
> > so I'm a bit confused how this case could happen.  I think we'll need
> > to
> > dig a bit deeper on what's actually happening here.
> 
> You are right.
> 
> I added some debug info.
> 
> [31948.771952] MYDEBUG: init kref: nvme_init_ctrl
> [31948.798589] MYDEBUG: get: nvme_rdma_create_ctrl
> [31948.803765] MYDEBUG: put: nvmf_dev_release
> [31948.808734] MYDEBUG: get: nvme_alloc_ns
> [31948.884775] MYDEBUG: put: nvme_free_ns
> [31948.890155] MYDEBUG in nvme_rdma_destroy_queue_ib: queue
> ffff8800cdc81470: io queue
> [31948.900539] MYDEBUG: put: nvme_rdma_del_ctrl_work
> [31948.909469] MYDEBUG: nvme_rdma_free_ctrl called
> [31948.915379] MYDEBUG in nvme_rdma_destroy_queue_ib: queue
> ffff8800cdc81400: admin queue
> 
> So nvme_rdma_destroy_queue_ib() was called for admin queue after ctrl was
> already freed.
> 
> With below patch, the debug info shows:
> 
> [32139.379831] MYDEBUG: get/init: nvme_init_ctrl
> [32139.407166] MYDEBUG: get: nvme_rdma_create_ctrl
> [32139.412463] MYDEBUG: put: nvmf_dev_release
> [32139.417697] MYDEBUG: get: nvme_alloc_ns
> [32139.418422] MYDEBUG: get: nvme_rdma_device_unplug
> [32139.474154] MYDEBUG: put: nvme_free_ns
> [32139.479406] MYDEBUG in nvme_rdma_destroy_queue_ib: queue
> ffff8800347c6470: io queue
> [32139.489532] MYDEBUG: put: nvme_rdma_del_ctrl_work
> [32139.496048] MYDEBUG in nvme_rdma_destroy_queue_ib: queue
> ffff8800347c6400: admin queue
> [32139.739089] MYDEBUG: put: nvme_rdma_device_unplug
> [32139.748175] MYDEBUG: nvme_rdma_free_ctrl called
> 
> and the crash was fixed.
> 
> What do you think?
> 
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index e1205c0..284d980 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -1323,6 +1323,12 @@ static int nvme_rdma_device_unplug(struct
> nvme_rdma_queue *queue)
>  	if (!test_and_clear_bit(NVME_RDMA_Q_CONNECTED, &queue->flags))
>  		goto out;
> 
> +	/*
> +	 * Grab a reference so the ctrl won't be freed before we free
> +	 * the last queue
> +	 */
> +	kref_get(&ctrl->ctrl.kref);
> +
>  	/* delete the controller */
>  	ret = __nvme_rdma_del_ctrl(ctrl);
>  	if (!ret) {
> @@ -1339,6 +1345,8 @@ static int nvme_rdma_device_unplug(struct
> nvme_rdma_queue *queue)
>  		nvme_rdma_destroy_queue_ib(queue);
>  	}
> 
> +	nvme_put_ctrl(&ctrl->ctrl);
> +
>  out:
>  	return ctrl_deleted;
>  }
> 

This change again avoids the first crash, but I still see the __ib_process_cq() crash.