[PATCH v3 2/9] nvme-fabrics: allow to queue requests for live queues

[Christoph Hellwig]

On Wed, Aug 19, 2020 at 10:36:44PM -0700, Sagi Grimberg wrote:
> Right now we are failing requests based on the controller state (which
> is checked inline in nvmf_check_ready) however we should definitely
> accept requests if the queue is live.
> 
> When entering controller reset, we transition the controller into
> NVME_CTRL_RESETTING, and then return BLK_STS_RESOURCE for non-mpath
> requests (have blk_noretry_request set).
> 
> This is also the case for NVME_REQ_USER for the wrong reason. There
> shouldn't be any reason for us to reject this I/O in a controller reset.
> We do want to prevent passthru commands on the admin queue because we
> need the controller to fully initialize first before we let user passthru
> admin commands to be issued.
> 
> In a non-mpath setup, this means that the requests will simply be
> requeued over and over forever not allowing the q_usage_counter to drop
> its final reference, causing controller reset to hang if running
> concurrently with heavy I/O.

I'm still rather bothered with the admin queue exception.  And given that
the q_usage_counter problem should only really be an issue for file system
requests, as passthrough requests do not automatically get retried why
can't we just reject all user command to be symetric and straight forward?
The callers in userspace need to be able to cope with retryable errors
anyway.

>  	/*
> +	 * currently we have a problem sending passthru commands
> +	 * on the admin_q if the controller is not LIVE because we can't
> +	 * make sure that they are going out after the admin connect,
> +	 * controller enable and/or other commands in the initialization
> +	 * sequence. until the controller will be LIVE, fail with
> +	 * BLK_STS_RESOURCE so that they will be rescheduled.
>  	 */

Nit: please start multi-line comments with a capital letter.  Also I
think some of the lines do not nearly use up the 80 characters available.