Subject: [PATCHv2 2/2] drivers/base: reorder consumer and its children behind suppliers

From: Pingfan Liu <[email-masked]>
Date: Mon, 25 Jun 2018 15:47:39 +0800

commit 52cdbdd49853 ("driver core: correct device's shutdown order")
introduces supplier<-consumer order in devices_kset. The commit tries
to cleverly maintain both parent<-child and supplier<-consumer order by
reordering a device when probing. This method makes things simple and
clean, but unfortunately, breaks parent<-child order in some case,
which is described in next patch in this series.
Here this patch tries to resolve supplier<-consumer by only reordering a
device when it has suppliers, and takes care of the following scenario:
    [consumer, children] [ ... potential ... ] supplier
                         ^                   ^
After moving the consumer and its children after the supplier, the
potentail section may contain consumers whose supplier is inside
children, and this poses the requirement to dry out all consumpers in
the section recursively.

Cc: Greg Kroah-Hartman <[email-masked]>
Cc: Grygorii Strashko <[email-masked]>
Cc: Christoph Hellwig <[email-masked]>
Cc: Bjorn Helgaas <[email-masked]>
Cc: Dave Young <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Signed-off-by: Pingfan Liu <[email-masked]>
---
note: there is lock issue in this patch, should be fixed in next version

---
 drivers/base/core.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 129 insertions(+), 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 66f06ff..db30e86 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -123,12 +123,138 @@ static int device_is_dependent(struct device *dev, void *target)
 	return ret;
 }
 
-/* a temporary place holder to mark out the root cause of the bug.
- * The proposal algorithm will come in next patch
+struct pos_info {
+	struct device *pos;
+	struct device *tail;
+};
+
+/* caller takes the devices_kset->list_lock */
+static int descendants_reorder_after_pos(struct device *dev,
+	void *data)
+{
+	struct device *pos;
+	struct pos_info *p = data;
+
+	pos = p->pos;
+	pr_debug("devices_kset: Moving %s after %s\n",
+		 dev_name(dev), dev_name(pos));
+	device_for_each_child(dev, p, descendants_reorder_after_pos);
+	/* children at the tail */
+	list_move(&dev->kobj.entry, &pos->kobj.entry);
+	/* record the right boundary of the section */
+	if (p->tail == NULL)
+		p->tail = dev;
+	return 0;
+}
+
+/* iterate over an open section */
+#define list_opensect_for_each_reverse(cur, left, right)	\
+	for (cur = right->prev; cur == left; cur = cur->prev)
+
+static bool is_consumer(struct device *query, struct device *supplier)
+{
+	struct device_link *link;
+	/* todo, lock protection */
+	list_for_each_entry(link, &supplier->links.consumers, s_node)
+		if (link->consumer == query)
+			return true;
+	return false;
+}
+
+/* recursively move the potential consumers in open section (left, right)
+ * after the barrier
+ */
+static int __device_reorder_consumer(struct device *consumer,
+	struct list_head *left, struct list_head *right,
+	struct pos_info *p)
+{
+	struct list_head *iter;
+	struct device *c_dev, *s_dev, *tail_dev;
+
+	descendants_reorder_after_pos(consumer, p);
+	tail_dev = p->tail;
+	/* (left, right) may contain consumers, hence checking if any moved
+	 * child serving as supplier. The reversing order help us to meet
+	 * the last supplier of a consumer.
+	 */
+	list_opensect_for_each_reverse(iter, left, right) {
+		struct list_head *l_iter, *moved_left, *moved_right;
+
+		moved_left = (&consumer->kobj.entry)->prev;
+		moved_right = tail_dev->kobj.entry.next;
+		/* the moved section may contain potential suppliers */
+		list_opensect_for_each_reverse(l_iter, moved_left,
+			moved_right) {
+			s_dev = list_entry(l_iter, struct device, kobj.entry);
+			c_dev = list_entry(iter, struct device, kobj.entry);
+			/* to fix: this poses extra effort for locking */
+			if (is_consumer(c_dev, s_dev)) {
+				p->tail = NULL;
+				/* to fix: lock issue */
+				p->pos =  s_dev;
+				/* reorder after the last supplier */
+				__device_reorder_consumer(c_dev,
+					l_iter, right, p);
+			}
+		}
+	}
+	return 0;
+}
+
+static int find_last_supplier(struct device *dev, struct device *supplier)
+{
+	struct device_link *link;
+
+	list_for_each_entry_reverse(link, &dev->links.suppliers, c_node) {
+		if (link->supplier == supplier)
+			return 1;
+	}
+	if (dev == supplier)
+		return -1;
+	return 0;
+}
+
+/* When reodering, take care of the range of (old_pos(dev), new_pos(dev)),
+ * there may be requirement to recursively move item.
  */
 int device_reorder_consumer(struct device *dev)
 {
-	devices_kset_move_last(dev);
+	struct list_head *iter, *left, *right;
+	struct device *cur_dev;
+	struct pos_info info;
+	int ret, idx;
+
+	idx = device_links_read_lock();
+	if (list_empty(&dev->links.suppliers)) {
+		device_links_read_unlock(idx);
+		return 0;
+	}
+	spin_lock(&devices_kset->list_lock);
+	list_for_each_prev(iter, &devices_kset->list) {
+		cur_dev = list_entry(iter, struct device, kobj.entry);
+		ret = find_last_supplier(dev, cur_dev);
+		switch (ret) {
+		case -1:
+			goto unlock;
+		case 1:
+			break;
+		case 0:
+			continue;
+		}
+	}
+	BUG_ON(!ret);
+
+	/* record the affected open section */
+	left = dev->kobj.entry.prev;
+	right = iter;
+	info.pos = list_entry(iter, struct device, kobj.entry);
+	info.tail = NULL;
+	/* dry out the consumers in (left,right) */
+	__device_reorder_consumer(dev, left, right, &info);
+
+unlock:
+	spin_unlock(&devices_kset->list_lock);
+	device_links_read_unlock(idx);
 	return 0;
 }
 
-- 
2.7.4