Re: [PATCH v4] dma-buf: fix racing conflict of dma_heap_add()

[Andrew Davis <afd@ti.com>]

On 11/4/22 11:05 AM, Dawei Li wrote:
> Racing conflict could be:
> task A                 task B
> list_for_each_entry
> strcmp(h->name))
>                         list_for_each_entry
>                         strcmp(h->name)
> kzalloc                kzalloc
> ......                 .....
> device_create          device_create
> list_add
>                         list_add
> 
> The root cause is that task B has no idea about the fact someone
> else(A) has inserted heap with same name when it calls list_add,
> so a potential collision occurs.
> 
> Fixes: c02a81fba74f ("dma-buf: Add dma-buf heaps framework")
> Signed-off-by: Dawei Li <set_pte_at@outlook.com>

LGTM, Thanks,

Acked-by: Andrew Davis <afd@ti.com>

> ---
> v1: https://lore.kernel.org/all/TYCP286MB2323950197F60FC3473123B7CA349@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM/
> v1->v2: Narrow down locking scope, check the existence of heap before
> insertion, as suggested by Andrew Davis.
> v2->v3: Remove double checking.
> v3->v4: Minor coding style and patch formatting adjustment.
> ---
>   drivers/dma-buf/dma-heap.c | 28 +++++++++++++++-------------
>   1 file changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 8f5848aa144f..59d158873f4c 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -233,18 +233,6 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   		return ERR_PTR(-EINVAL);
>   	}
>   
> -	/* check the name is unique */
> -	mutex_lock(&heap_list_lock);
> -	list_for_each_entry(h, &heap_list, list) {
> -		if (!strcmp(h->name, exp_info->name)) {
> -			mutex_unlock(&heap_list_lock);
> -			pr_err("dma_heap: Already registered heap named %s\n",
> -			       exp_info->name);
> -			return ERR_PTR(-EINVAL);
> -		}
> -	}
> -	mutex_unlock(&heap_list_lock);
> -
>   	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
>   	if (!heap)
>   		return ERR_PTR(-ENOMEM);
> @@ -283,13 +271,27 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   		err_ret = ERR_CAST(dev_ret);
>   		goto err2;
>   	}
> -	/* Add heap to the list */
> +
>   	mutex_lock(&heap_list_lock);
> +	/* check the name is unique */
> +	list_for_each_entry(h, &heap_list, list) {
> +		if (!strcmp(h->name, exp_info->name)) {
> +			mutex_unlock(&heap_list_lock);
> +			pr_err("dma_heap: Already registered heap named %s\n",
> +			       exp_info->name);
> +			err_ret = ERR_PTR(-EINVAL);
> +			goto err3;
> +		}
> +	}
> +
> +	/* Add heap to the list */
>   	list_add(&heap->list, &heap_list);
>   	mutex_unlock(&heap_list_lock);
>   
>   	return heap;
>   
> +err3:
> +	device_destroy(dma_heap_class, heap->heap_devt);
>   err2:
>   	cdev_del(&heap->heap_cdev);
>   err1: