Re: [PATCH v3 2/3] resource: Add release_mem_region_adjustable()

[Toshi Kani]

On Wed, 2013-04-10 at 15:24 -0700, Andrew Morton wrote:
> On Wed, 10 Apr 2013 15:08:29 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote:
> 
> > On Wed, 10 Apr 2013, Toshi Kani wrote:
> > 
> > > > I'll switch it to GFP_ATOMIC.  Which is horridly lame but the
> > > > allocation is small and alternatives are unobvious.
> > > 
> > > Great!  Again, thanks for the update!
> > 
> > release_mem_region_adjustable() allocates at most one struct resource, so 
> > why not do kmalloc(sizeof(struct resource), GFP_KERNEL) before taking 
> > resource_lock and then testing whether it's NULL or not when splitting?  
> > It unnecessarily allocates memory when there's no split, but 
> > __remove_pages() shouldn't be a hotpath.
> 
> yup.
> 
> --- a/kernel/resource.c~resource-add-release_mem_region_adjustable-fix-fix
> +++ a/kernel/resource.c
> @@ -1046,7 +1046,8 @@ int release_mem_region_adjustable(struct
>  			resource_size_t start, resource_size_t size)
>  {
>  	struct resource **p;
> -	struct resource *res, *new;
> +	struct resource *res;
> +	struct resource *new_res;
>  	resource_size_t end;
>  	int ret = -EINVAL;
>  
> @@ -1054,6 +1055,9 @@ int release_mem_region_adjustable(struct
>  	if ((start < parent->start) || (end > parent->end))
>  		return ret;
>  
> +	/* The kzalloc() result gets checked later */
> +	new_res = kzalloc(sizeof(struct resource), GFP_KERNEL);
> +
>  	p = &parent->child;
>  	write_lock(&resource_lock);
>  
> @@ -1091,32 +1095,33 @@ int release_mem_region_adjustable(struct
>  						start - res->start);
>  		} else {
>  			/* split into two entries */
> -			new = kzalloc(sizeof(struct resource), GFP_ATOMIC);
> -			if (!new) {
> +			if (!new_res) {
>  				ret = -ENOMEM;
>  				break;
>  			}
> -			new->name = res->name;
> -			new->start = end + 1;
> -			new->end = res->end;
> -			new->flags = res->flags;
> -			new->parent = res->parent;
> -			new->sibling = res->sibling;
> -			new->child = NULL;
> +			new_res->name = res->name;
> +			new_res->start = end + 1;
> +			new_res->end = res->end;
> +			new_res->flags = res->flags;
> +			new_res->parent = res->parent;
> +			new_res->sibling = res->sibling;
> +			new_res->child = NULL;
>  
>  			ret = __adjust_resource(res, res->start,
>  						start - res->start);
>  			if (ret) {
> -				kfree(new);
> +				kfree(new_res);
>  				break;
>  			}

The kfree() in the if-statement above is not necessary since kfree() is
called before the return at the end.  That is, the if-statement needs to
be:
	if (ret)
		break;

With this change, I confirmed that all my test cases passed (with all
the config debug options this time :).  With the change:

Reviewed-by: Toshi Kani <toshi.kani@xxxxxx>
Tested-by: Toshi Kani <toshi.kani@xxxxxx>

Thanks!
-Toshi


> -			res->sibling = new;
> +			res->sibling = new_res;
> +			new_res = NULL;
>  		}
>  
>  		break;
>  	}
>  
>  	write_unlock(&resource_lock);
> +	kfree(new_res);
>  	return ret;
>  }
>  #endif	/* CONFIG_MEMORY_HOTPLUG */
> _
> 


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