Re: [PATCH v5 5/7] mm, hmm: Use devm semantics for hmm_devmem_{add, remove}

[Jerome Glisse <jglisse@redhat.com>]

On Wed, Sep 12, 2018 at 07:22:27PM -0700, Dan Williams wrote:
> devm semantics arrange for resources to be torn down when
> device-driver-probe fails or when device-driver-release completes.
> Similar to devm_memremap_pages() there is no need to support an explicit
> remove operation when the users properly adhere to devm semantics.
> 
> Note that devm_kzalloc() automatically handles allocating node-local
> memory.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Jerome Glisse <jglisse@redhat.com>

> Cc: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  include/linux/hmm.h |    4 --
>  mm/hmm.c            |  127 ++++++++++-----------------------------------------
>  2 files changed, 25 insertions(+), 106 deletions(-)
> 
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 4c92e3ba3e16..5ec8635f602c 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -499,8 +499,7 @@ struct hmm_devmem {
>   * enough and allocate struct page for it.
>   *
>   * The device driver can wrap the hmm_devmem struct inside a private device
> - * driver struct. The device driver must call hmm_devmem_remove() before the
> - * device goes away and before freeing the hmm_devmem struct memory.
> + * driver struct.
>   */
>  struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  				  struct device *device,
> @@ -508,7 +507,6 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
>  					   struct device *device,
>  					   struct resource *res);
> -void hmm_devmem_remove(struct hmm_devmem *devmem);
>  
>  /*
>   * hmm_devmem_page_set_drvdata - set per-page driver data field
> diff --git a/mm/hmm.c b/mm/hmm.c
> index c968e49f7a0c..ec1d9eccf176 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -939,7 +939,6 @@ static void hmm_devmem_ref_exit(void *data)
>  
>  	devmem = container_of(ref, struct hmm_devmem, ref);
>  	percpu_ref_exit(ref);
> -	devm_remove_action(devmem->device, &hmm_devmem_ref_exit, data);
>  }
>  
>  static void hmm_devmem_ref_kill(void *data)
> @@ -950,7 +949,6 @@ static void hmm_devmem_ref_kill(void *data)
>  	devmem = container_of(ref, struct hmm_devmem, ref);
>  	percpu_ref_kill(ref);
>  	wait_for_completion(&devmem->completion);
> -	devm_remove_action(devmem->device, &hmm_devmem_ref_kill, data);
>  }
>  
>  static int hmm_devmem_fault(struct vm_area_struct *vma,
> @@ -988,7 +986,7 @@ static void hmm_devmem_radix_release(struct resource *resource)
>  	mutex_unlock(&hmm_devmem_lock);
>  }
>  
> -static void hmm_devmem_release(struct device *dev, void *data)
> +static void hmm_devmem_release(void *data)
>  {
>  	struct hmm_devmem *devmem = data;
>  	struct resource *resource = devmem->resource;
> @@ -996,11 +994,6 @@ static void hmm_devmem_release(struct device *dev, void *data)
>  	struct zone *zone;
>  	struct page *page;
>  
> -	if (percpu_ref_tryget_live(&devmem->ref)) {
> -		dev_WARN(dev, "%s: page mapping is still live!\n", __func__);
> -		percpu_ref_put(&devmem->ref);
> -	}
> -
>  	/* pages are dead and unused, undo the arch mapping */
>  	start_pfn = (resource->start & ~(PA_SECTION_SIZE - 1)) >> PAGE_SHIFT;
>  	npages = ALIGN(resource_size(resource), PA_SECTION_SIZE) >> PAGE_SHIFT;
> @@ -1124,19 +1117,6 @@ static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
>  	return ret;
>  }
>  
> -static int hmm_devmem_match(struct device *dev, void *data, void *match_data)
> -{
> -	struct hmm_devmem *devmem = data;
> -
> -	return devmem->resource == match_data;
> -}
> -
> -static void hmm_devmem_pages_remove(struct hmm_devmem *devmem)
> -{
> -	devres_release(devmem->device, &hmm_devmem_release,
> -		       &hmm_devmem_match, devmem->resource);
> -}
> -
>  /*
>   * hmm_devmem_add() - hotplug ZONE_DEVICE memory for device memory
>   *
> @@ -1164,8 +1144,7 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  
>  	dev_pagemap_get_ops();
>  
> -	devmem = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
> -				   GFP_KERNEL, dev_to_node(device));
> +	devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
>  	if (!devmem)
>  		return ERR_PTR(-ENOMEM);
>  
> @@ -1179,11 +1158,11 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  	ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
>  			      0, GFP_KERNEL);
>  	if (ret)
> -		goto error_percpu_ref;
> +		return ERR_PTR(ret);
>  
> -	ret = devm_add_action(device, hmm_devmem_ref_exit, &devmem->ref);
> +	ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit, &devmem->ref);
>  	if (ret)
> -		goto error_devm_add_action;
> +		return ERR_PTR(ret);
>  
>  	size = ALIGN(size, PA_SECTION_SIZE);
>  	addr = min((unsigned long)iomem_resource.end,
> @@ -1203,16 +1182,12 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  
>  		devmem->resource = devm_request_mem_region(device, addr, size,
>  							   dev_name(device));
> -		if (!devmem->resource) {
> -			ret = -ENOMEM;
> -			goto error_no_resource;
> -		}
> +		if (!devmem->resource)
> +			return ERR_PTR(-ENOMEM);
>  		break;
>  	}
> -	if (!devmem->resource) {
> -		ret = -ERANGE;
> -		goto error_no_resource;
> -	}
> +	if (!devmem->resource)
> +		return ERR_PTR(-ERANGE);
>  
>  	devmem->resource->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
>  	devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
> @@ -1221,28 +1196,13 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  
>  	ret = hmm_devmem_pages_create(devmem);
>  	if (ret)
> -		goto error_pages;
> -
> -	devres_add(device, devmem);
> +		return ERR_PTR(ret);
>  
> -	ret = devm_add_action(device, hmm_devmem_ref_kill, &devmem->ref);
> -	if (ret) {
> -		hmm_devmem_remove(devmem);
> +	ret = devm_add_action_or_reset(device, hmm_devmem_release, devmem);
> +	if (ret)
>  		return ERR_PTR(ret);
> -	}
>  
>  	return devmem;
> -
> -error_pages:
> -	devm_release_mem_region(device, devmem->resource->start,
> -				resource_size(devmem->resource));
> -error_no_resource:
> -error_devm_add_action:
> -	hmm_devmem_ref_kill(&devmem->ref);
> -	hmm_devmem_ref_exit(&devmem->ref);
> -error_percpu_ref:
> -	devres_free(devmem);
> -	return ERR_PTR(ret);
>  }
>  EXPORT_SYMBOL(hmm_devmem_add);
>  
> @@ -1258,8 +1218,7 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
>  
>  	dev_pagemap_get_ops();
>  
> -	devmem = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
> -				   GFP_KERNEL, dev_to_node(device));
> +	devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
>  	if (!devmem)
>  		return ERR_PTR(-ENOMEM);
>  
> @@ -1273,12 +1232,12 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
>  	ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
>  			      0, GFP_KERNEL);
>  	if (ret)
> -		goto error_percpu_ref;
> +		return ERR_PTR(ret);
>  
> -	ret = devm_add_action(device, hmm_devmem_ref_exit, &devmem->ref);
> +	ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit,
> +			&devmem->ref);
>  	if (ret)
> -		goto error_devm_add_action;
> -
> +		return ERR_PTR(ret);
>  
>  	devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
>  	devmem->pfn_last = devmem->pfn_first +
> @@ -1286,59 +1245,21 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
>  
>  	ret = hmm_devmem_pages_create(devmem);
>  	if (ret)
> -		goto error_devm_add_action;
> +		return ERR_PTR(ret);
>  
> -	devres_add(device, devmem);
> +	ret = devm_add_action_or_reset(device, hmm_devmem_release, devmem);
> +	if (ret)
> +		return ERR_PTR(ret);
>  
> -	ret = devm_add_action(device, hmm_devmem_ref_kill, &devmem->ref);
> -	if (ret) {
> -		hmm_devmem_remove(devmem);
> +	ret = devm_add_action_or_reset(device, hmm_devmem_ref_kill,
> +			&devmem->ref);
> +	if (ret)
>  		return ERR_PTR(ret);
> -	}
>  
>  	return devmem;
> -
> -error_devm_add_action:
> -	hmm_devmem_ref_kill(&devmem->ref);
> -	hmm_devmem_ref_exit(&devmem->ref);
> -error_percpu_ref:
> -	devres_free(devmem);
> -	return ERR_PTR(ret);
>  }
>  EXPORT_SYMBOL(hmm_devmem_add_resource);
>  
> -/*
> - * hmm_devmem_remove() - remove device memory (kill and free ZONE_DEVICE)
> - *
> - * @devmem: hmm_devmem struct use to track and manage the ZONE_DEVICE memory
> - *
> - * This will hot-unplug memory that was hotplugged by hmm_devmem_add on behalf
> - * of the device driver. It will free struct page and remove the resource that
> - * reserved the physical address range for this device memory.
> - */
> -void hmm_devmem_remove(struct hmm_devmem *devmem)
> -{
> -	resource_size_t start, size;
> -	struct device *device;
> -	bool cdm = false;
> -
> -	if (!devmem)
> -		return;
> -
> -	device = devmem->device;
> -	start = devmem->resource->start;
> -	size = resource_size(devmem->resource);
> -
> -	cdm = devmem->resource->desc == IORES_DESC_DEVICE_PUBLIC_MEMORY;
> -	hmm_devmem_ref_kill(&devmem->ref);
> -	hmm_devmem_ref_exit(&devmem->ref);
> -	hmm_devmem_pages_remove(devmem);
> -
> -	if (!cdm)
> -		devm_release_mem_region(device, start, size);
> -}
> -EXPORT_SYMBOL(hmm_devmem_remove);
> -
>  /*
>   * A device driver that wants to handle multiple devices memory through a
>   * single fake device can use hmm_device to do so. This is purely a helper
>