nvme-pci: NULL pointer dereference in nvme_dev_disable() on linux-next

[Sagi Grimberg]

> Below is the minimal fix.  I'll see if I sort out the mess that is
> probe/reset failure vs ->remove a bit better, though.
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index f94b05c585cbc..577bacdcfee08 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -5160,6 +5160,8 @@ EXPORT_SYMBOL_GPL(nvme_start_freeze);
>   
>   void nvme_stop_queues(struct nvme_ctrl *ctrl)
>   {
> +	if (!ctrl->tagset)
> +		return;
>   	if (!test_and_set_bit(NVME_CTRL_STOPPED, &ctrl->flags))
>   		blk_mq_quiesce_tagset(ctrl->tagset);
>   	else
> @@ -5169,6 +5171,8 @@ EXPORT_SYMBOL_GPL(nvme_stop_queues);
>   
>   void nvme_start_queues(struct nvme_ctrl *ctrl)
>   {
> +	if (!ctrl->tagset)
> +		return;
>   	if (test_and_clear_bit(NVME_CTRL_STOPPED, &ctrl->flags))
>   		blk_mq_unquiesce_tagset(ctrl->tagset);
>   }

Can we do that in the pci driver and not here?