Fix accounting error for pending sync IO ops in zpool iostat

Currently vdev_queue_class_length is responsible for checking how long
the queue length is, however, it doesn't check the length when a list
is used, rather it just returns whether it is empty or not. To fix this
I added a counter variable to vdev_queue_class to keep track of the sync
IO ops, and changed vdev_queue_class_length to reference this variable
instead.

Along with this I removed the list_size field from the list
implementations as it was only being used in few ASSERTS. It also allows
us to make these changes without increasing the maximum size of
vdev_queue_class.

Signed-off-by: MigeljanImeri <ImeriMigel@gmail.com>

include/os/freebsd/spl/sys/list_impl.h

@@ -39,7 +39,6 @@ struct list_node {
 };
 
 struct list {
-	size_t	list_size;
 	size_t	list_offset;
 	struct list_node list_head;
 };

include/os/linux/spl/sys/list.h

@@ -48,7 +48,6 @@
 typedef struct list_head list_node_t;
 
 typedef struct list {
-	size_t list_size;
 	size_t list_offset;
 	list_node_t list_head;
 } list_t;
@@ -72,7 +71,8 @@ list_link_init(list_node_t *node)
 static inline void
 list_create(list_t *list, size_t size, size_t offset)
 {
-	list->list_size = size;
+	(void) size;
+
 	list->list_offset = offset;
 	INIT_LIST_HEAD(&list->list_head);
 }

include/sys/vdev_impl.h

@@ -131,7 +131,10 @@ typedef const struct vdev_ops {
  * Virtual device properties
  */
 typedef union vdev_queue_class {
-	list_t		vqc_list;
+	struct {
+		ulong_t 	vqc_list_numnodes;
+		list_t		vqc_list;
+	};
 	avl_tree_t	vqc_tree;
 } vdev_queue_class_t;
 

lib/libspl/include/sys/list_impl.h

@@ -39,8 +39,7 @@ struct list_node {
 };
 
 struct list {
-	size_t	list_size;
-	size_t	list_offset;
+	size_t list_offset;
 	struct list_node list_head;
 };
 

lib/libspl/list.c

@@ -62,10 +62,9 @@ void
 list_create(list_t *list, size_t size, size_t offset)
 {
 	ASSERT(list);
-	ASSERT(size > 0);
-	ASSERT(size >= offset + sizeof (list_node_t));
 
-	list->list_size = size;
+	(void) size;
+
 	list->list_offset = offset;
 	list->list_head.next = list->list_head.prev = &list->list_head;
 }
@@ -194,7 +193,6 @@ list_move_tail(list_t *dst, list_t *src)
 	list_node_t *dstnode = &dst->list_head;
 	list_node_t *srcnode = &src->list_head;
 
-	ASSERT(dst->list_size == src->list_size);
 	ASSERT(dst->list_offset == src->list_offset);
 
 	if (list_empty(src))

module/os/freebsd/spl/list.c

@@ -62,9 +62,9 @@ void
 list_create(list_t *list, size_t size, size_t offset)
 {
 	ASSERT3P(list, !=, NULL);
-	ASSERT3U(size, >=, offset + sizeof (list_node_t));
 
-	list->list_size = size;
+	(void) size;
+
 	list->list_offset = offset;
 	list->list_head.list_next = list->list_head.list_prev =
 	    &list->list_head;
@@ -194,7 +194,6 @@ list_move_tail(list_t *dst, list_t *src)
 	list_node_t *dstnode = &dst->list_head;
 	list_node_t *srcnode = &src->list_head;
 
-	ASSERT3U(dst->list_size, ==, src->list_size);
 	ASSERT3U(dst->list_offset, ==, src->list_offset);
 
 	if (list_empty(src))

module/zfs/vdev_queue.c

@@ -273,8 +273,10 @@ vdev_queue_class_add(vdev_queue_t *vq, zio_t *zio)
 {
 	zio_priority_t p = zio->io_priority;
 	vq->vq_cqueued |= 1U << p;
-	if (vdev_queue_class_fifo(p))
+	if (vdev_queue_class_fifo(p)) {
 		list_insert_tail(&vq->vq_class[p].vqc_list, zio);
+		vq->vq_class[p].vqc_list_numnodes++;
+	}
 	else
 		avl_add(&vq->vq_class[p].vqc_tree, zio);
 }
@@ -288,6 +290,7 @@ vdev_queue_class_remove(vdev_queue_t *vq, zio_t *zio)
 		list_t *list = &vq->vq_class[p].vqc_list;
 		list_remove(list, zio);
 		empty = list_is_empty(list);
+		vq->vq_class[p].vqc_list_numnodes--;
 	} else {
 		avl_tree_t *tree = &vq->vq_class[p].vqc_tree;
 		avl_remove(tree, zio);
@@ -1069,7 +1072,7 @@ vdev_queue_class_length(vdev_t *vd, zio_priority_t p)
 {
 	vdev_queue_t *vq = &vd->vdev_queue;
 	if (vdev_queue_class_fifo(p))
-		return (list_is_empty(&vq->vq_class[p].vqc_list) == 0);
+		return (vq->vq_class[p].vqc_list_numnodes);
 	else
 		return (avl_numnodes(&vq->vq_class[p].vqc_tree));
 }