Re: [PATCH v3 09/16] block/mq-deadline: Improve compile-time argument checking

[Adam Manzanares <a.manzanares@samsung.com>]

On Thu, Jun 17, 2021 at 05:44:49PM -0700, Bart Van Assche wrote:
> Modern compilers complain if an out-of-range value is passed to a function
> argument that has an enumeration type. Let the compiler detect out-of-range
> data direction arguments instead of verifying the data_dir argument at
> runtime.
> 
> Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
> Cc: Damien Le Moal <damien.lemoal@wdc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  block/mq-deadline.c | 96 +++++++++++++++++++++++----------------------
>  1 file changed, 49 insertions(+), 47 deletions(-)
> 
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index d823ba7cb084..69126beff77d 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -35,6 +35,13 @@ static const int writes_starved = 2;    /* max times reads can starve a write */
>  static const int fifo_batch = 16;       /* # of sequential requests treated as one
>  				     by the above parameters. For throughput. */
>  
> +enum dd_data_dir {
> +	DD_READ		= READ,
> +	DD_WRITE	= WRITE,
> +};
> +
> +enum { DD_DIR_COUNT = 2 };
> +
>  struct deadline_data {
>  	/*
>  	 * run time data
> @@ -43,20 +50,20 @@ struct deadline_data {
>  	/*
>  	 * requests (deadline_rq s) are present on both sort_list and fifo_list
>  	 */
> -	struct rb_root sort_list[2];
> -	struct list_head fifo_list[2];
> +	struct rb_root sort_list[DD_DIR_COUNT];
> +	struct list_head fifo_list[DD_DIR_COUNT];
>  
>  	/*
>  	 * next in sort order. read, write or both are NULL
>  	 */
> -	struct request *next_rq[2];
> +	struct request *next_rq[DD_DIR_COUNT];
>  	unsigned int batching;		/* number of sequential requests made */
>  	unsigned int starved;		/* times reads have starved writes */
>  
>  	/*
>  	 * settings that change how the i/o scheduler behaves
>  	 */
> -	int fifo_expire[2];
> +	int fifo_expire[DD_DIR_COUNT];
>  	int fifo_batch;
>  	int writes_starved;
>  	int front_merges;
> @@ -97,7 +104,7 @@ deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
>  static inline void
>  deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
>  {
> -	const int data_dir = rq_data_dir(rq);
> +	const enum dd_data_dir data_dir = rq_data_dir(rq);
>  
>  	if (dd->next_rq[data_dir] == rq)
>  		dd->next_rq[data_dir] = deadline_latter_request(rq);
> @@ -169,10 +176,10 @@ static void dd_merged_requests(struct request_queue *q, struct request *req,
>  static void
>  deadline_move_request(struct deadline_data *dd, struct request *rq)
>  {
> -	const int data_dir = rq_data_dir(rq);
> +	const enum dd_data_dir data_dir = rq_data_dir(rq);
>  
> -	dd->next_rq[READ] = NULL;
> -	dd->next_rq[WRITE] = NULL;
> +	dd->next_rq[DD_READ] = NULL;
> +	dd->next_rq[DD_WRITE] = NULL;
>  	dd->next_rq[data_dir] = deadline_latter_request(rq);
>  
>  	/*
> @@ -185,9 +192,10 @@ deadline_move_request(struct deadline_data *dd, struct request *rq)
>   * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
>   * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
>   */
> -static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
> +static inline int deadline_check_fifo(struct deadline_data *dd,
> +				      enum dd_data_dir data_dir)
>  {
> -	struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
> +	struct request *rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
>  
>  	/*
>  	 * rq is expired!
> @@ -203,19 +211,16 @@ static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
>   * dispatch using arrival ordered lists.
>   */
>  static struct request *
> -deadline_fifo_request(struct deadline_data *dd, int data_dir)
> +deadline_fifo_request(struct deadline_data *dd, enum dd_data_dir data_dir)
>  {
>  	struct request *rq;
>  	unsigned long flags;
>  
> -	if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
> -		return NULL;
> -
>  	if (list_empty(&dd->fifo_list[data_dir]))
>  		return NULL;
>  
>  	rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
> -	if (data_dir == READ || !blk_queue_is_zoned(rq->q))
> +	if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q))
>  		return rq;
>  
>  	/*
> @@ -223,7 +228,7 @@ deadline_fifo_request(struct deadline_data *dd, int data_dir)
>  	 * an unlocked target zone.
>  	 */
>  	spin_lock_irqsave(&dd->zone_lock, flags);
> -	list_for_each_entry(rq, &dd->fifo_list[WRITE], queuelist) {
> +	list_for_each_entry(rq, &dd->fifo_list[DD_WRITE], queuelist) {
>  		if (blk_req_can_dispatch_to_zone(rq))
>  			goto out;
>  	}
> @@ -239,19 +244,16 @@ deadline_fifo_request(struct deadline_data *dd, int data_dir)
>   * dispatch using sector position sorted lists.
>   */
>  static struct request *
> -deadline_next_request(struct deadline_data *dd, int data_dir)
> +deadline_next_request(struct deadline_data *dd, enum dd_data_dir data_dir)
>  {
>  	struct request *rq;
>  	unsigned long flags;
>  
> -	if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
> -		return NULL;
> -
>  	rq = dd->next_rq[data_dir];
>  	if (!rq)
>  		return NULL;
>  
> -	if (data_dir == READ || !blk_queue_is_zoned(rq->q))
> +	if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q))
>  		return rq;
>  
>  	/*
> @@ -276,7 +278,7 @@ deadline_next_request(struct deadline_data *dd, int data_dir)
>  static struct request *__dd_dispatch_request(struct deadline_data *dd)
>  {
>  	struct request *rq, *next_rq;
> -	int data_dir;
> +	enum dd_data_dir data_dir;
>  
>  	lockdep_assert_held(&dd->lock);
>  
> @@ -289,9 +291,9 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
>  	/*
>  	 * batches are currently reads XOR writes
>  	 */
> -	rq = deadline_next_request(dd, WRITE);
> +	rq = deadline_next_request(dd, DD_WRITE);
>  	if (!rq)
> -		rq = deadline_next_request(dd, READ);
> +		rq = deadline_next_request(dd, DD_READ);
>  
>  	if (rq && dd->batching < dd->fifo_batch)
>  		/* we have a next request are still entitled to batch */
> @@ -302,14 +304,14 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
>  	 * data direction (read / write)
>  	 */
>  
> -	if (!list_empty(&dd->fifo_list[READ])) {
> -		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
> +	if (!list_empty(&dd->fifo_list[DD_READ])) {
> +		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[DD_READ]));
>  
> -		if (deadline_fifo_request(dd, WRITE) &&
> +		if (deadline_fifo_request(dd, DD_WRITE) &&
>  		    (dd->starved++ >= dd->writes_starved))
>  			goto dispatch_writes;
>  
> -		data_dir = READ;
> +		data_dir = DD_READ;
>  
>  		goto dispatch_find_request;
>  	}
> @@ -318,13 +320,13 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
>  	 * there are either no reads or writes have been starved
>  	 */
>  
> -	if (!list_empty(&dd->fifo_list[WRITE])) {
> +	if (!list_empty(&dd->fifo_list[DD_WRITE])) {
>  dispatch_writes:
> -		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
> +		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[DD_WRITE]));
>  
>  		dd->starved = 0;
>  
> -		data_dir = WRITE;
> +		data_dir = DD_WRITE;
>  
>  		goto dispatch_find_request;
>  	}
> @@ -399,8 +401,8 @@ static void dd_exit_sched(struct elevator_queue *e)
>  {
>  	struct deadline_data *dd = e->elevator_data;
>  
> -	BUG_ON(!list_empty(&dd->fifo_list[READ]));
> -	BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
> +	BUG_ON(!list_empty(&dd->fifo_list[DD_READ]));
> +	BUG_ON(!list_empty(&dd->fifo_list[DD_WRITE]));
>  
>  	kfree(dd);
>  }
> @@ -424,12 +426,12 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
>  	}
>  	eq->elevator_data = dd;
>  
> -	INIT_LIST_HEAD(&dd->fifo_list[READ]);
> -	INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
> -	dd->sort_list[READ] = RB_ROOT;
> -	dd->sort_list[WRITE] = RB_ROOT;
> -	dd->fifo_expire[READ] = read_expire;
> -	dd->fifo_expire[WRITE] = write_expire;
> +	INIT_LIST_HEAD(&dd->fifo_list[DD_READ]);
> +	INIT_LIST_HEAD(&dd->fifo_list[DD_WRITE]);
> +	dd->sort_list[DD_READ] = RB_ROOT;
> +	dd->sort_list[DD_WRITE] = RB_ROOT;
> +	dd->fifo_expire[DD_READ] = read_expire;
> +	dd->fifo_expire[DD_WRITE] = write_expire;
>  	dd->writes_starved = writes_starved;
>  	dd->front_merges = 1;
>  	dd->fifo_batch = fifo_batch;
> @@ -497,7 +499,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
>  {
>  	struct request_queue *q = hctx->queue;
>  	struct deadline_data *dd = q->elevator->elevator_data;
> -	const int data_dir = rq_data_dir(rq);
> +	const enum dd_data_dir data_dir = rq_data_dir(rq);
>  
>  	lockdep_assert_held(&dd->lock);
>  
> @@ -585,7 +587,7 @@ static void dd_finish_request(struct request *rq)
>  
>  		spin_lock_irqsave(&dd->zone_lock, flags);
>  		blk_req_zone_write_unlock(rq);
> -		if (!list_empty(&dd->fifo_list[WRITE]))
> +		if (!list_empty(&dd->fifo_list[DD_WRITE]))
>  			blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
>  		spin_unlock_irqrestore(&dd->zone_lock, flags);
>  	}
> @@ -626,8 +628,8 @@ static ssize_t __FUNC(struct elevator_queue *e, char *page)		\
>  		__data = jiffies_to_msecs(__data);			\
>  	return deadline_var_show(__data, (page));			\
>  }
> -SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
> -SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
> +SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[DD_READ], 1);
> +SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[DD_WRITE], 1);
>  SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
>  SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
>  SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
> @@ -649,8 +651,8 @@ static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)
>  		*(__PTR) = __data;					\
>  	return count;							\
>  }
> -STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
> -STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
> +STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[DD_READ], 0, INT_MAX, 1);
> +STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[DD_WRITE], 0, INT_MAX, 1);
>  STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
>  STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
>  STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
> @@ -717,8 +719,8 @@ static int deadline_##name##_next_rq_show(void *data,			\
>  		__blk_mq_debugfs_rq_show(m, rq);			\
>  	return 0;							\
>  }
> -DEADLINE_DEBUGFS_DDIR_ATTRS(READ, read)
> -DEADLINE_DEBUGFS_DDIR_ATTRS(WRITE, write)
> +DEADLINE_DEBUGFS_DDIR_ATTRS(DD_READ, read)
> +DEADLINE_DEBUGFS_DDIR_ATTRS(DD_WRITE, write)
>  #undef DEADLINE_DEBUGFS_DDIR_ATTRS
>  
>  static int deadline_batching_show(void *data, struct seq_file *m)

Looks good.

Reviewed by: Adam Manzanares <a.manzanares@samsung.com>