linux-kernel - Re: [PATCH] nvme-core: Fix subsystem instance mismatches

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Message-ID: <f07e03f1-48f0-591e-fdf6-9499fa4dd9ab@deltatee.com>
Date:   Wed, 4 Sep 2019 11:01:22 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...com>,
        Hannes Reinecke <hare@...e.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Keith Busch <keith.busch@...el.com>
Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches



On 2019-09-04 10:35 a.m., Keith Busch wrote:
> On Wed, Sep 04, 2019 at 10:07:12AM -0600, Logan Gunthorpe wrote:
>> Yes, I agree, we can't solve the mismatch problem in the general case:
>> with sequences of hot plug events there will always be a case that
>> mismatches. I just think we can do better in the simple common default case.
> 
> This may be something where udev can help us. I might be able to find
> some time to look at that, but not today.
>  
>>> Can we just ensure there is never a matching controller then? This
>>> patch will accomplish that and simpler than wrapping the instance in a
>>> refcount'ed object:
>>>
>>> http://lists.infradead.org/pipermail/linux-nvme/2019-May/024142.html
>>
>> I don't really like that idea. It reduces the confusion caused by
>> mismatching numbers, but causes the controller to never match the
>> namespace, which is also confusing but in a different way.
>>
>> I like the nvme_instance idea. It's not going to be perfect but it has
>> some nice properties: the subsystem will try to match the controller's
>> instance whenever possible, but in cases where it doesn't, the instance
>> number of the subsystem will never be the same as an existing controller.
>>
>> I'll see if I can work up a quick patch set and see what people think.
> 
> How about this: we have the subsys copy the controller's instance,
> and the nvme_free_ctrl() doesn't release it if its subsys matches?

Oh, yes that's simpler than the struct/kref method and looks like it
will accomplish the same thing. I did some brief testing with it and it
seems to work for me (though I don't have any subsystems with multiple
controllers). If you want to make a patch out of it you can add my

Reviewed-by: Logan Gunthorpe <logang@...tatee.com>

Thanks!

Logan

> ---
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 14c0bfb55615..8a8279ece5ee 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -81,7 +81,6 @@ EXPORT_SYMBOL_GPL(nvme_reset_wq);
>  struct workqueue_struct *nvme_delete_wq;
>  EXPORT_SYMBOL_GPL(nvme_delete_wq);
>  
> -static DEFINE_IDA(nvme_subsystems_ida);
>  static LIST_HEAD(nvme_subsystems);
>  static DEFINE_MUTEX(nvme_subsystems_lock);
>  
> @@ -2344,7 +2343,8 @@ static void nvme_release_subsystem(struct device *dev)
>  	struct nvme_subsystem *subsys =
>  		container_of(dev, struct nvme_subsystem, dev);
>  
> -	ida_simple_remove(&nvme_subsystems_ida, subsys->instance);
> +	if (subsys->instance >= 0)
> +		ida_simple_remove(&nvme_instance_ida, subsys->instance);
>  	kfree(subsys);
>  }
>  
> @@ -2473,12 +2473,8 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>  	subsys = kzalloc(sizeof(*subsys), GFP_KERNEL);
>  	if (!subsys)
>  		return -ENOMEM;
> -	ret = ida_simple_get(&nvme_subsystems_ida, 0, 0, GFP_KERNEL);
> -	if (ret < 0) {
> -		kfree(subsys);
> -		return ret;
> -	}
> -	subsys->instance = ret;
> +
> +	subsys->instance = -1;
>  	mutex_init(&subsys->lock);
>  	kref_init(&subsys->ref);
>  	INIT_LIST_HEAD(&subsys->ctrls);
> @@ -2497,7 +2493,7 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>  	subsys->dev.class = nvme_subsys_class;
>  	subsys->dev.release = nvme_release_subsystem;
>  	subsys->dev.groups = nvme_subsys_attrs_groups;
> -	dev_set_name(&subsys->dev, "nvme-subsys%d", subsys->instance);
> +	dev_set_name(&subsys->dev, "nvme-subsys%d", ctrl->instance);
>  	device_initialize(&subsys->dev);
>  
>  	mutex_lock(&nvme_subsystems_lock);
> @@ -2528,6 +2524,8 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
>  		goto out_put_subsystem;
>  	}
>  
> +	if (!found)
> +		subsys->instance = ctrl->instance;
>  	ctrl->subsys = subsys;
>  	list_add_tail(&ctrl->subsys_entry, &subsys->ctrls);
>  	mutex_unlock(&nvme_subsystems_lock);
> @@ -3803,7 +3801,9 @@ static void nvme_free_ctrl(struct device *dev)
>  		container_of(dev, struct nvme_ctrl, ctrl_device);
>  	struct nvme_subsystem *subsys = ctrl->subsys;
>  
> -	ida_simple_remove(&nvme_instance_ida, ctrl->instance);
> +	if (subsys && ctrl->instance != subsys->instance)
> +		ida_simple_remove(&nvme_instance_ida, ctrl->instance);
> +
>  	kfree(ctrl->effects);
>  	nvme_mpath_uninit(ctrl);
>  	__free_page(ctrl->discard_page);
> @@ -4085,7 +4085,6 @@ static int __init nvme_core_init(void)
>  
>  static void __exit nvme_core_exit(void)
>  {
> -	ida_destroy(&nvme_subsystems_ida);
>  	class_destroy(nvme_subsys_class);
>  	class_destroy(nvme_class);
>  	unregister_chrdev_region(nvme_chr_devt, NVME_MINORS);
> --
>