[PATCH] nvme-core: flush namespace scanning work just before removing namespaces

[keith.busch@intel.com (Keith Busch)]

On Wed, Nov 21, 2018@03:17:37PM -0800, Sagi Grimberg wrote:
> nvme_stop_ctrl can be called also for reset flow and there is no need to
> flush the scan_work as namespaces are not being removed. This can cause
> deadlock in rdma, fc and loop drivers since nvme_stop_ctrl barriers
> before controller teardown (and specifically I/O cancellation of the
> scan_work itself) takes place, but the scan_work will be blocked anyways
> so there is no need to flush it.
> 
> Instead, move scan_work flush to nvme_remove_namespaces() where it really
> needs to flush.
> 
> Reported-by: Ming Lei <ming.lei at redhat.com>
> Signed-off-by: Sagi Grimberg <sagi at grimberg.me>

Looks good to me.

Reviewed-by: Keith Busch <keith.busch at intel.com>

> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3327,6 +3327,9 @@ void nvme_remove_namespaces(struct nvme_ctrl *ctrl)
>  	struct nvme_ns *ns, *next;
>  	LIST_HEAD(ns_list);
>  
> +	/* prevent racing with ns scanning */
> +	flush_work(&ctrl->scan_work);
> +
>  	/*
>  	 * The dead states indicates the controller was not gracefully
>  	 * disconnected. In that case, we won't be able to flush any data while
> @@ -3489,7 +3492,6 @@ void nvme_stop_ctrl(struct nvme_ctrl *ctrl)
>  	nvme_mpath_stop(ctrl);
>  	nvme_stop_keep_alive(ctrl);
>  	flush_work(&ctrl->async_event_work);
> -	flush_work(&ctrl->scan_work);
>  	cancel_work_sync(&ctrl->fw_act_work);
>  	if (ctrl->ops->stop_ctrl)
>  		ctrl->ops->stop_ctrl(ctrl);
> --