[PATCH 2/2] nvme: don't do scan work if io queue count is zero

[Sagi Grimberg]

> kernel panic when try to rescan ns when io queue count is zero.Because
> kernel BUG_ON when hctx_idx is greater than ctrl->queue_count.
> --
> nvme_rdma_init_hctx+0x58/0x60 [nvme_rdma]
> blk_mq_realloc_hw_ctxs+0x140/0x4c0
> blk_mq_init_allocated_queue+0x130/0x410
> blk_mq_init_queue+0x40/0x88
> nvme_validate_ns+0xb8/0x740
> nvme_scan_work+0x29c/0x460
> process_one_work+0x1f8/0x490
> worker_thread+0x50/0x4b8
> kthread+0x134/0x138
> ret_from_fork+0x10/0x18
> --
> Defence it by not allowing rescan ns when io queue count is zero.
> 
> Signed-off-by: Ruozhu Li <liruozhu at huawei.com>
> ---
>   drivers/nvme/host/core.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index dfd9dec0c1f6..d9f837eb3e26 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -141,7 +141,8 @@ void nvme_queue_scan(struct nvme_ctrl *ctrl)
>   	/*
>   	 * Only new queue scan work when admin and IO queues are both alive
>   	 */
> -	if (ctrl->state == NVME_CTRL_LIVE && ctrl->tagset)
> +	if (ctrl->state == NVME_CTRL_LIVE &&
> +	    ctrl->tagset && ctrl->queue_count > 1)
>   		queue_work(nvme_wq, &ctrl->scan_work);
>   }
>   
> @@ -4047,7 +4048,8 @@ static void nvme_scan_work(struct work_struct *work)
>   		container_of(work, struct nvme_ctrl, scan_work);
>   
>   	/* No tagset on a live ctrl means IO queues could not created */
> -	if (ctrl->state != NVME_CTRL_LIVE || !ctrl->tagset)
> +	if (ctrl->state != NVME_CTRL_LIVE ||
> +	    !ctrl->tagset || ctrl->queue_count < 2)
>   		return;

We can't keep growing sporadic conditionals here, its becoming a mess...