Re: parallel nvme format

[Keith Busch <kbusch@kernel.org>]

On Thu, Dec 14, 2023 at 02:49:54PM -0800, Keith Busch wrote:
> On Thu, Dec 14, 2023 at 09:21:28PM +0000, Niklas Cassel wrote:
> > Perhaps we could introduce a new bit, NVME_CTRL_NEEDS_SCAN or similar?
> > (That gets cleared by nvme_scan_work(), after a scan has been performed.)
> 
> Good point. Updated patch below.
>  
> > I guess for format command specifically, we already have
> > NVME_AER_NOTICE_NS_CHANGED, but that seems to be cleared before by
> > nvme_scan_work() before the mutex is acquired.
> 
> The clearing should just re-arm the controller to send the AER again if
> any other namespace changes. But we can't really depend on the AER
> anyway.
> 
> > And I'm not sure if all command that have
> > effects & (NVME_CMD_EFFECTS_NIC | NVME_CMD_EFFECTS_NCC)
> > set will trigger a NVME_AER_NOTICE_NS_CHANGED AEN.
> 
> We have the "known_effects" for the format command to ensure the driver
> will always request a rescan on a format no matter what a controller
> reports, but yeah, the format could be followed up by another command
> with NVME_CMD_EFFECTS_CSE_MASK set without NIC/NCC, so definitely need
> to retain the need to restart the scan.

The previous diff missed the header update:

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 39a90b7cb1254..79a71b6ae64fe 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -251,6 +251,7 @@ enum nvme_ctrl_flags {
 	NVME_CTRL_STOPPED		= 3,
 	NVME_CTRL_SKIP_ID_CNS_CS	= 4,
 	NVME_CTRL_DIRTY_CAPABILITY	= 5,
+	NVME_CTRL_NEEDS_RESCAN		= 6,
 };

 struct nvme_ctrl {
 
> ---
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 590cd4f097c22..0b062a2268447 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1120,6 +1120,8 @@ u32 nvme_passthru_start(struct nvme_ctrl *ctrl, struct nvme_ns *ns, u8 opcode)
>  		nvme_start_freeze(ctrl);
>  		nvme_wait_freeze(ctrl);
>  	}
> +	if (effects & (NVME_CMD_EFFECTS_NIC | NVME_CMD_EFFECTS_NCC))
> +		set_bit(NVME_CTRL_NEEDS_RESCAN, &ctrl->flags);
>  	return effects;
>  }
>  EXPORT_SYMBOL_NS_GPL(nvme_passthru_start, NVME_TARGET_PASSTHRU);
> @@ -1140,7 +1142,7 @@ void nvme_passthru_end(struct nvme_ctrl *ctrl, struct nvme_ns *ns, u32 effects,
>  "controller capabilities changed, reset may be required to take effect.\n");
>  		}
>  	}
> -	if (effects & (NVME_CMD_EFFECTS_NIC | NVME_CMD_EFFECTS_NCC)) {
> +	if (test_bit(NVME_CTRL_NEEDS_RESCAN, &ctrl->flags)) {
>  		nvme_queue_scan(ctrl);
>  		flush_work(&ctrl->scan_work);
>  	}
> @@ -3945,7 +3947,14 @@ static void nvme_scan_work(struct work_struct *work)
>  		nvme_clear_changed_ns_log(ctrl);
>  	}
>  
> -	mutex_lock(&ctrl->scan_lock);
> +	/*
> +	 * Failure to acquire scan_lock means another thread will requeue this
> +	 * work shortly
> +	 */
> +	if (!mutex_trylock(&ctrl->scan_lock))
> +		return;
> +
> +	clear_bit(NVME_CTRL_NEEDS_RESCAN, &ctrl->flags);
>  	if (nvme_ctrl_limited_cns(ctrl)) {
>  		nvme_scan_ns_sequential(ctrl);
>  	} else {
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 39a90b7cb1254..79a71b6ae64fe 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -251,6 +251,7 @@ enum nvme_ctrl_flags {
>  	NVME_CTRL_STOPPED		= 3,
>  	NVME_CTRL_SKIP_ID_CNS_CS	= 4,
>  	NVME_CTRL_DIRTY_CAPABILITY	= 5,
> +	NVME_CTRL_NEEDS_RESCAN		= 6,
>  };
>  
>  struct nvme_ctrl {
> --
>