[1/3] wiphy: make wiphy work queue reentrant

Commit Message

James Prestwood May 11, 2023, 6:48 p.m. UTC

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.

Currently FT reschedules the same work item in the 'do_work'
callback but this patch actually allows for rescheduling as long
as the item is currently running, even if do_work has returned and
waiting for wiphy_radio_work_done.

A few new flags were added to the radio work item. One which is
set when the item is running which prevents other items from being
inserted ahead (previously done with priority=INT_MIN). This is
needed since we cannot modify the priority anymore in case the item
is being rescheduled.

The another flag is set when the item was rescheduled. Once the
item is finished the 'rescheduled' flag is checked and the item
will be removed and re-inserted into the queue if needed.
---
 src/wiphy.c | 69 ++++++++++++++++++++++++++++++++++++++++++-----------
 src/wiphy.h |  2 ++
 2 files changed, 57 insertions(+), 14 deletions(-)

Patch

diff --git a/src/wiphy.c b/src/wiphy.c
index 2db2d2cd..e6ca3b76 100644
--- a/src/wiphy.c
+++ b/src/wiphy.c
@@ -2570,6 +2570,17 @@  static void wiphy_reg_notify(struct l_genl_msg *msg, void *user_data)
 	wiphy_dump_after_regdom(wiphy);
 }
 
+static int insert_by_priority(const void *a, const void *b, void *user_data)
+{
+	const struct wiphy_radio_work_item *new = a;
+	const struct wiphy_radio_work_item *work = b;
+
+	if (work->running || work->priority <= new->priority)
+		return 1;
+
+	return -1;
+}
+
 static void wiphy_radio_work_next(struct wiphy *wiphy)
 {
 	struct wiphy_radio_work_item *work;
@@ -2583,7 +2594,7 @@  static void wiphy_radio_work_next(struct wiphy *wiphy)
 	 * Ensures no other work item will get inserted before this one while
 	 * the work is being done.
 	 */
-	work->priority = INT_MIN;
+	work->running = true;
 
 	l_debug("Starting work item %u", work->id);
 
@@ -2592,7 +2603,12 @@  static void wiphy_radio_work_next(struct wiphy *wiphy)
 	wiphy->work_in_callback = false;
 
 	if (done) {
-		work->id = 0;
+		bool rescheduled = work->rescheduled;
+
+		work->running = false;
+
+		if (!rescheduled)
+			work->id = 0;
 
 		l_queue_remove(wiphy->work, work);
 
@@ -2600,26 +2616,49 @@  static void wiphy_radio_work_next(struct wiphy *wiphy)
 		destroy_work(work);
 		wiphy->work_in_callback = false;
 
+		/*
+		 * If the item was rescheduled inside do_work() we can safely
+		 * insert it here, otherwise destroy_work() could have freed it.
+		 * The item could have been re-inserted inside destroy_work()
+		 * but this is safe since the item was removed from the queue.
+		 */
+		if (rescheduled) {
+			work->rescheduled = false;
+			l_queue_insert(wiphy->work, work,
+					insert_by_priority, NULL);
+		}
+
 		wiphy_radio_work_next(wiphy);
 	}
 }
 
-static int insert_by_priority(const void *a, const void *b, void *user_data)
-{
-	const struct wiphy_radio_work_item *new = a;
-	const struct wiphy_radio_work_item *work = b;
-
-	if (work->priority <= new->priority)
-		return 1;
-
-	return -1;
-}
-
 uint32_t wiphy_radio_work_insert(struct wiphy *wiphy,
 				struct wiphy_radio_work_item *item,
 				int priority,
 				const struct wiphy_radio_work_item_ops *ops)
 {
+	/*
+	 * Handling the case of re-inserting the same work item that is in
+	 * progress. A non-started work item should never be re-inserted
+	 * into the queue. Keep the same ID, priority, and ops. If these somehow
+	 * are different the caller should really be using a separate work item.
+	 * Once the item is finished it will be removed and re-inserted based
+	 * on the rescheduled flag.
+	 */
+	if (item == l_queue_peek_head(wiphy->work)) {
+		/*
+		 * Shouldn't cause problems, but at least warn the caller they
+		 * should really be using a separate item
+		 */
+		L_WARN_ON(item->rescheduled || item->priority != priority ||
+				ops != item->ops);
+
+		item->rescheduled = true;
+		l_debug("Rescheduled work item %u", item->id);
+
+		return item->id;
+	}
+
 	item->priority = priority;
 	item->ops = ops;
 	item->id = ++work_ids;
@@ -2656,6 +2695,7 @@  void wiphy_radio_work_done(struct wiphy *wiphy, uint32_t id)
 	if (item->id == id) {
 		next = true;
 		l_queue_pop_head(wiphy->work);
+		item->running = false;
 	} else
 		item = l_queue_remove_if(wiphy->work, match_id,
 						L_UINT_TO_PTR(id));
@@ -2664,7 +2704,8 @@  void wiphy_radio_work_done(struct wiphy *wiphy, uint32_t id)
 
 	l_debug("Work item %u done", id);
 
-	item->id = 0;
+	if (!item->rescheduled)
+		item->id = 0;
 
 	wiphy->work_in_callback = true;
 	destroy_work(item);
diff --git a/src/wiphy.h b/src/wiphy.h
index d5d1cc8f..b6861f5f 100644
--- a/src/wiphy.h
+++ b/src/wiphy.h
@@ -45,6 +45,8 @@  struct wiphy_radio_work_item {
 	uint32_t id;
 	int priority;
 	const struct wiphy_radio_work_item_ops *ops;
+	bool rescheduled : 1;
+	bool running : 1;
 };
 
 enum {