Re: [PATCH 1/2] device-dax/kmem: Fix resource release

[David Hildenbrand]

On 15.10.20 02:42, Dan Williams wrote:
> The conversion to request_mem_region() is broken because it assumes that
> the range is marked busy prior to release. However, due to the way that
> the kmem driver manipulates the IORESOURCE_BUSY flag (clears it to
> let {add,remove}_memory() handle busy) it requires a manual
> release_resource() to perform cleanup.
> 
> Given that the actual 'struct resource *' needs to be recalled, not just
> the range, add that tracking to the kmem driver-data.
> 
> Reported-by: David Hildenbrand <david@xxxxxxxxxx>
> Fixes: 0513bd5bb114 ("device-dax/kmem: replace release_resource() with release_mem_region()")
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Cc: Brice Goglin <Brice.Goglin@xxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Jia He <justin.he@xxxxxxx>
> Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  drivers/dax/kmem.c |   48 ++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 34 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 6c933f2b604e..af04b6d1d263 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -35,11 +35,17 @@ static int dax_kmem_range(struct dev_dax *dev_dax, int i, struct range *r)
>  	return 0;
>  }
>  
> +struct dax_kmem_data {
> +	const char *res_name;
> +	struct resource *res[];
> +};
> +
>  static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  {
>  	struct device *dev = &dev_dax->dev;
> +	struct dax_kmem_data *data;
> +	int rc = -ENOMEM;
>  	int i, mapped = 0;
> -	char *res_name;
>  	int numa_node;
>  
>  	/*
> @@ -55,14 +61,17 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  		return -EINVAL;
>  	}
>  
> -	res_name = kstrdup(dev_name(dev), GFP_KERNEL);
> -	if (!res_name)
> +	data = kzalloc(sizeof(*data) + sizeof(struct resource *) * dev_dax->nr_range, GFP_KERNEL);
> +	if (!data)
>  		return -ENOMEM;
>  
> +	data->res_name = kstrdup(dev_name(dev), GFP_KERNEL);
> +	if (!data->res_name)
> +		goto err_res_name;
> +
>  	for (i = 0; i < dev_dax->nr_range; i++) {
>  		struct resource *res;
>  		struct range range;
> -		int rc;
>  
>  		rc = dax_kmem_range(dev_dax, i, &range);
>  		if (rc) {
> @@ -72,7 +81,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  		}
>  
>  		/* Region is permanently reserved if hotremove fails. */
> -		res = request_mem_region(range.start, range_len(&range), res_name);
> +		res = request_mem_region(range.start, range_len(&range), data->res_name);
>  		if (!res) {
>  			dev_warn(dev, "mapping%d: %#llx-%#llx could not reserve region\n",
>  					i, range.start, range.end);
> @@ -82,9 +91,10 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  			 */
>  			if (mapped)
>  				continue;
> -			kfree(res_name);
> -			return -EBUSY;
> +			rc = -EBUSY;
> +			goto err_request_mem;
>  		}
> +		data->res[i] = res;
>  
>  		/*
>  		 * Set flags appropriate for System RAM.  Leave ..._BUSY clear
> @@ -104,18 +114,25 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  		if (rc) {
>  			dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n",
>  					i, range.start, range.end);
> -			release_mem_region(range.start, range_len(&range));
> +			release_resource(res);
> +			kfree(res);
> +			data->res[i] = NULL;
>  			if (mapped)
>  				continue;
> -			kfree(res_name);
> -			return rc;
> +			goto err_request_mem;
>  		}
>  		mapped++;
>  	}
>  
> -	dev_set_drvdata(dev, res_name);
> +	dev_set_drvdata(dev, data);
>  
>  	return 0;
> +
> +err_request_mem:
> +	kfree(data->res_name);
> +err_res_name:
> +	kfree(data);
> +	return rc;
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTREMOVE
> @@ -123,7 +140,7 @@ static int dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  {
>  	int i, success = 0;
>  	struct device *dev = &dev_dax->dev;
> -	const char *res_name = dev_get_drvdata(dev);
> +	struct dax_kmem_data *data = dev_get_drvdata(dev);
>  
>  	/*
>  	 * We have one shot for removing memory, if some memory blocks were not
> @@ -142,7 +159,9 @@ static int dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  		rc = remove_memory(dev_dax->target_node, range.start,
>  				range_len(&range));
>  		if (rc == 0) {
> -			release_mem_region(range.start, range_len(&range));
> +			release_resource(data->res[i]);
> +			kfree(data->res[i]);
> +			data->res[i] = NULL;
>  			success++;
>  			continue;
>  		}
> @@ -153,7 +172,8 @@ static int dev_dax_kmem_remove(struct dev_dax *dev_dax)
>  	}
>  
>  	if (success >= dev_dax->nr_range) {
> -		kfree(res_name);
> +		kfree(data->res_name);
> +		kfree(data);
>  		dev_set_drvdata(dev, NULL);
>  	}
>  
> 

Looks sane to me

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

-- 
Thanks,

David / dhildenb