Re: [PATCH 2/2] s390/mm: Use refcount_t for refcount

[David Hildenbrand <david@redhat.com>]

On 08.08.19 09:18, Chuhong Yuan wrote:
> Reference counters are preferred to use refcount_t instead of
> atomic_t.
> This is because the implementation of refcount_t can prevent
> overflows and detect possible use-after-free.
> So convert atomic_t ref counters to refcount_t.
> 
> Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> ---
>  arch/s390/include/asm/gmap.h |  4 +++-
>  arch/s390/mm/gmap.c          | 10 +++++-----
>  2 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h
> index fcbd638fb9f4..37f96b6f0e61 100644
> --- a/arch/s390/include/asm/gmap.h
> +++ b/arch/s390/include/asm/gmap.h
> @@ -9,6 +9,8 @@
>  #ifndef _ASM_S390_GMAP_H
>  #define _ASM_S390_GMAP_H
>  
> +#include <linux/refcount.h>
> +
>  /* Generic bits for GMAP notification on DAT table entry changes. */
>  #define GMAP_NOTIFY_SHADOW	0x2
>  #define GMAP_NOTIFY_MPROT	0x1
> @@ -46,7 +48,7 @@ struct gmap {
>  	struct radix_tree_root guest_to_host;
>  	struct radix_tree_root host_to_guest;
>  	spinlock_t guest_table_lock;
> -	atomic_t ref_count;
> +	refcount_t ref_count;
>  	unsigned long *table;
>  	unsigned long asce;
>  	unsigned long asce_end;
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 39c3a6e3d262..cd8e03f04d6d 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -67,7 +67,7 @@ static struct gmap *gmap_alloc(unsigned long limit)
>  	INIT_RADIX_TREE(&gmap->host_to_rmap, GFP_ATOMIC);
>  	spin_lock_init(&gmap->guest_table_lock);
>  	spin_lock_init(&gmap->shadow_lock);
> -	atomic_set(&gmap->ref_count, 1);
> +	refcount_set(&gmap->ref_count, 1);
>  	page = alloc_pages(GFP_KERNEL, CRST_ALLOC_ORDER);
>  	if (!page)
>  		goto out_free;
> @@ -214,7 +214,7 @@ static void gmap_free(struct gmap *gmap)
>   */
>  struct gmap *gmap_get(struct gmap *gmap)
>  {
> -	atomic_inc(&gmap->ref_count);
> +	refcount_inc(&gmap->ref_count);
>  	return gmap;
>  }
>  EXPORT_SYMBOL_GPL(gmap_get);
> @@ -227,7 +227,7 @@ EXPORT_SYMBOL_GPL(gmap_get);
>   */
>  void gmap_put(struct gmap *gmap)
>  {
> -	if (atomic_dec_return(&gmap->ref_count) == 0)
> +	if (refcount_dec_and_test(&gmap->ref_count))
>  		gmap_free(gmap);
>  }
>  EXPORT_SYMBOL_GPL(gmap_put);
> @@ -1594,7 +1594,7 @@ static struct gmap *gmap_find_shadow(struct gmap *parent, unsigned long asce,
>  			continue;
>  		if (!sg->initialized)
>  			return ERR_PTR(-EAGAIN);
> -		atomic_inc(&sg->ref_count);
> +		refcount_inc(&sg->ref_count);
>  		return sg;
>  	}
>  	return NULL;
> @@ -1682,7 +1682,7 @@ struct gmap *gmap_shadow(struct gmap *parent, unsigned long asce,
>  			}
>  		}
>  	}
> -	atomic_set(&new->ref_count, 2);
> +	refcount_set(&new->ref_count, 2);
>  	list_add(&new->list, &parent->children);
>  	if (asce & _ASCE_REAL_SPACE) {
>  		/* nothing to protect, return right away */
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb