Re: [PATCH 2/2] nvme: delete disk when last path is gone

[Minwoo Im <minwoo.im.dev@gmail.com>]

On 21-02-23 12:59:22, Hannes Reinecke wrote:
> The multipath code currently deletes the disk only after all references
> to it are dropped rather than when the last path to that disk is lost.
> This has been reported to cause problems with some use cases like MD RAID.
> 
> This patch implements an alternative behaviour of deleting the disk when
> the last path is gone, ie the same behaviour as non-multipathed nvme
> devices. The new behaviour will be selected with the 'fail_if_no_path'
> attribute, as returning it's arguably the same functionality.
> 
> Suggested-by: Keith Busch <kbusch@kernel.org>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
>  drivers/nvme/host/core.c      |  1 +
>  drivers/nvme/host/multipath.c |  3 ++-
>  drivers/nvme/host/nvme.h      | 17 +++++++++++++++--
>  3 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 2fb3ecc0c53b..d717a6283d6e 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -542,6 +542,7 @@ static void nvme_free_ns_head(struct kref *ref)
>  		container_of(ref, struct nvme_ns_head, ref);
>  
>  	nvme_mpath_remove_disk(head);
> +	nvme_mpath_put_disk(head);
>  	ida_simple_remove(&head->subsys->ns_ida, head->instance);
>  	cleanup_srcu_struct(&head->srcu);
>  	nvme_put_subsystem(head->subsys);
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index d5773ea105b1..f995b8234622 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -724,6 +724,8 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
>  
>  void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>  {
> +	if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
> +		return;
>  	if (!head->disk)
>  		return;
>  	if (head->disk->flags & GENHD_FL_UP)
> @@ -741,7 +743,6 @@ void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>  		 */
>  		head->disk->queue = NULL;
>  	}
> -	put_disk(head->disk);
>  }
>  
>  int nvme_mpath_init(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 3d2513f8194d..e6efa085f08a 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -681,8 +681,12 @@ static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
>  {
>  	struct nvme_ns_head *head = ns->head;
>  
> -	if (head->disk && list_empty(&head->list))
> -		kblockd_schedule_work(&head->requeue_work);
> +	if (head->disk && list_empty(&head->list)) {
> +		if (test_bit(NVME_NSHEAD_FAIL_IF_NO_PATH, &head->flags))
> +			nvme_mpath_remove_disk(head);

Does it need to call nvme_mpath_remove_disk here ?  It looks like it
returns with nothing right away if NVME_NSHEAD_FAIL_IF_NO_PATH is set.

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