wiphy: make wiphy work queue reentrant

In some situations its convenient for the same work item to be
inserted (rescheduled) while its in progress. FT for example does
this now if a roam fails. The same ft_work item gets re-inserted
which, currently, is not safe to do since the item is modified
and removed once completed.

Fix this by introducing wiphy_radio_work_reschedule which is an
explicit API for re-inserting work items from within the do_work
callback.

The wiphy work logic was changed around slightly to remove the item
at the head of the queue prior to starting and note the ID going
into do_work. If do_work signaled done and ID changed we know it
was re-inserted and can skip the destroy logic and move onto the
next item. If the item is not done continue as normal but set the
priority to INT_MIN, as usual, to prevent other items from getting
to the head of the queue.

src/wiphy.c

@@ -2574,16 +2574,13 @@ static void wiphy_radio_work_next(struct wiphy *wiphy)
 {
 	struct wiphy_radio_work_item *work;
 	bool done;
+	uint32_t id;
 
-	work = l_queue_peek_head(wiphy->work);
+	work = l_queue_pop_head(wiphy->work);
 	if (!work)
 		return;
 
-	/*
+	id = work->id;
-	 * Ensures no other work item will get inserted before this one while
-	 * the work is being done.
-	 */
-	work->priority = INT_MIN;
 
 	l_debug("Starting work item %u", work->id);
 
@@ -2592,15 +2589,25 @@ static void wiphy_radio_work_next(struct wiphy *wiphy)
 	wiphy->work_in_callback = false;
 
 	if (done) {
-		work->id = 0;
+		/* Item was rescheduled, don't destroy */
+		if (work->id != id)
+			goto next;
 
-		l_queue_remove(wiphy->work, work);
+		work->id = 0;
 
 		wiphy->work_in_callback = true;
 		destroy_work(work);
 		wiphy->work_in_callback = false;
 
+next:
 		wiphy_radio_work_next(wiphy);
+	} else {
+		/*
+		 * Ensures no other work item will get inserted before this one
+		 * while the work is being done.
+		 */
+		work->priority = INT_MIN;
+		l_queue_push_head(wiphy->work, work);
 	}
 }
 
@@ -2684,6 +2691,28 @@ int wiphy_radio_work_is_running(struct wiphy *wiphy, uint32_t id)
 	return item == l_queue_peek_head(wiphy->work) ? 1 : 0;
 }
 
+uint32_t wiphy_radio_work_reschedule(struct wiphy *wiphy,
+					struct wiphy_radio_work_item *item)
+{
+	/*
+	 * This should only be called from within the do_work callback, meaning
+	 * the item should not be in the queue. Any re-insertion on a running
+	 * item after do_work is not allowed.
+	 */
+	if (L_WARN_ON(wiphy_radio_work_is_running(wiphy, item->id) != -ENOENT))
+		return 0;
+
+	work_ids++;
+
+	l_debug("Rescheduling work item %u, new id %u", item->id, work_ids);
+
+	item->id = work_ids;
+
+	l_queue_insert(wiphy->work, item, insert_by_priority, NULL);
+
+	return item->id;
+}
+
 static int wiphy_init(void)
 {
 	struct l_genl *genl = iwd_get_genl();

src/wiphy.h

@@ -168,3 +168,5 @@ uint32_t wiphy_radio_work_insert(struct wiphy *wiphy,
 				const struct wiphy_radio_work_item_ops *ops);
 void wiphy_radio_work_done(struct wiphy *wiphy, uint32_t id);
 int wiphy_radio_work_is_running(struct wiphy *wiphy, uint32_t id);
+uint32_t wiphy_radio_work_reschedule(struct wiphy *wiphy,
+					struct wiphy_radio_work_item *item);