[dm-devel] [PATCH 3/3] dm zoned: target: use refcount_t for dm zoned reference counters

[Damien Le Moal]

John,

On 2018/08/23 10:37, John Pittman wrote:
> The API surrounding refcount_t should be used in place of atomic_t
> when variables are being used as reference counters.  This API can
> prevent issues such as counter overflows and use-after-free
> conditions.  Within the dm zoned target stack, the atomic_t API is
> used for bioctx->ref and cw->refcount.  Change these to use
> refcount_t, avoiding the issues mentioned.
> 
> Signed-off-by: John Pittman <jpittman at redhat.com>
> ---
>  drivers/md/dm-zoned-target.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/md/dm-zoned-target.c b/drivers/md/dm-zoned-target.c
> index a44183ff4be0..fa36825c1eff 100644
> --- a/drivers/md/dm-zoned-target.c
> +++ b/drivers/md/dm-zoned-target.c
> @@ -19,7 +19,7 @@ struct dmz_bioctx {
>  	struct dmz_target	*target;
>  	struct dm_zone		*zone;
>  	struct bio		*bio;
> -	atomic_t		ref;
> +	refcount_t		ref;
>  	blk_status_t		status;
>  };
>  
> @@ -28,7 +28,7 @@ struct dmz_bioctx {
>   */
>  struct dm_chunk_work {
>  	struct work_struct	work;
> -	atomic_t		refcount;
> +	refcount_t		refcount;
>  	struct dmz_target	*target;
>  	unsigned int		chunk;
>  	struct bio_list		bio_list;
> @@ -115,7 +115,7 @@ static int dmz_submit_read_bio(struct dmz_target *dmz, struct dm_zone *zone,
>  	if (nr_blocks == dmz_bio_blocks(bio)) {
>  		/* Setup and submit the BIO */
>  		bio->bi_iter.bi_sector = sector;
> -		atomic_inc(&bioctx->ref);
> +		refcount_inc(&bioctx->ref);
>  		generic_make_request(bio);
>  		return 0;
>  	}
> @@ -134,7 +134,7 @@ static int dmz_submit_read_bio(struct dmz_target *dmz, struct dm_zone *zone,
>  	bio_advance(bio, clone->bi_iter.bi_size);
>  
>  	/* Submit the clone */
> -	atomic_inc(&bioctx->ref);
> +	refcount_inc(&bioctx->ref);
>  	generic_make_request(clone);
>  
>  	return 0;
> @@ -240,7 +240,7 @@ static void dmz_submit_write_bio(struct dmz_target *dmz, struct dm_zone *zone,
>  	/* Setup and submit the BIO */
>  	bio_set_dev(bio, dmz->dev->bdev);
>  	bio->bi_iter.bi_sector = dmz_start_sect(dmz->metadata, zone) + dmz_blk2sect(chunk_block);
> -	atomic_inc(&bioctx->ref);
> +	refcount_inc(&bioctx->ref);
>  	generic_make_request(bio);
>  
>  	if (dmz_is_seq(zone))
> @@ -456,7 +456,7 @@ static void dmz_handle_bio(struct dmz_target *dmz, struct dm_chunk_work *cw,
>   */
>  static inline void dmz_get_chunk_work(struct dm_chunk_work *cw)
>  {
> -	atomic_inc(&cw->refcount);
> +	refcount_inc(&cw->refcount);
>  }
>  
>  /*
> @@ -465,7 +465,7 @@ static inline void dmz_get_chunk_work(struct dm_chunk_work *cw)
>   */
>  static void dmz_put_chunk_work(struct dm_chunk_work *cw)
>  {
> -	if (atomic_dec_and_test(&cw->refcount)) {
> +	if (refcount_dec_and_test(&cw->refcount)) {
>  		WARN_ON(!bio_list_empty(&cw->bio_list));
>  		radix_tree_delete(&cw->target->chunk_rxtree, cw->chunk);
>  		kfree(cw);
> @@ -546,7 +546,7 @@ static void dmz_queue_chunk_work(struct dmz_target *dmz, struct bio *bio)
>  			goto out;
>  
>  		INIT_WORK(&cw->work, dmz_chunk_work);
> -		atomic_set(&cw->refcount, 0);
> +		refcount_set(&cw->refcount, 0);
>  		cw->target = dmz;
>  		cw->chunk = chunk;
>  		bio_list_init(&cw->bio_list);
> @@ -599,7 +599,7 @@ static int dmz_map(struct dm_target *ti, struct bio *bio)
>  	bioctx->target = dmz;
>  	bioctx->zone = NULL;
>  	bioctx->bio = bio;
> -	atomic_set(&bioctx->ref, 1);
> +	refcount_set(&bioctx->ref, 1);
>  	bioctx->status = BLK_STS_OK;
>  
>  	/* Set the BIO pending in the flush list */
> @@ -633,7 +633,7 @@ static int dmz_end_io(struct dm_target *ti, struct bio *bio, blk_status_t *error
>  	if (bioctx->status == BLK_STS_OK && *error)
>  		bioctx->status = *error;
>  
> -	if (!atomic_dec_and_test(&bioctx->ref))
> +	if (!refcount_dec_and_test(&bioctx->ref))
>  		return DM_ENDIO_INCOMPLETE;
>  
>  	/* Done */
> 

Reviewed-by: Damien Le Moal <damien.lemoal at wdc.com>
Tested-by: Damien Le Moal <damien.lemoal at wdc.com>

Thanks !

-- 
Damien Le Moal
Western Digital Research