[PATCH v3] usb: ucsi: Ensure connector delayed work items are flushed

[Jack Pham <quic_jackp@quicinc.com>]

During ucsi_unregister() when destroying a connector's workqueue, there
may still be pending delayed work items that haven't been scheduled yet.
Because queue_delayed_work() uses a separate timer to schedule a work
item, the destroy_workqueue() call is not aware of any pending items.
Hence when a pending item's timer expires it would then try to queue on
a dangling workqueue pointer.

Fix this by keeping track of all work items in a list, so that prior to
destroying the workqueue any pending items can be flushed.  Do this by
calling mod_delayed_work() as that will cause pending items to get
queued immediately, which then allows the ensuing destroy_workqueue() to
implicitly drain all currently queued items to completion and free
themselves.

Fixes: b9aa02ca39a4 ("usb: typec: ucsi: Add polling mechanism for partner tasks like alt mode checking")
Suggested-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Co-developed-by: Linyu Yuan <quic_linyyuan@quicinc.com>
Signed-off-by: Linyu Yuan <quic_linyyuan@quicinc.com>
Signed-off-by: Jack Pham <quic_jackp@quicinc.com>
---
v3: Adopted Heikki's suggestion to track work items in a list. Updated subject
    and commit description again.
v2: update commit description and remove cc stable list

 drivers/usb/typec/ucsi/ucsi.c | 24 +++++++++++++++++++++---
 drivers/usb/typec/ucsi/ucsi.h |  1 +
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
index eabe519013e7..1292241d581a 100644
--- a/drivers/usb/typec/ucsi/ucsi.c
+++ b/drivers/usb/typec/ucsi/ucsi.c
@@ -187,6 +187,7 @@ EXPORT_SYMBOL_GPL(ucsi_send_command);
 
 struct ucsi_work {
 	struct delayed_work work;
+	struct list_head node;
 	unsigned long delay;
 	unsigned int count;
 	struct ucsi_connector *con;
@@ -202,6 +203,7 @@ static void ucsi_poll_worker(struct work_struct *work)
 	mutex_lock(&con->lock);
 
 	if (!con->partner) {
+		list_del(&uwork->node);
 		mutex_unlock(&con->lock);
 		kfree(uwork);
 		return;
@@ -209,10 +211,12 @@ static void ucsi_poll_worker(struct work_struct *work)
 
 	ret = uwork->cb(con);
 
-	if (uwork->count-- && (ret == -EBUSY || ret == -ETIMEDOUT))
+	if (uwork->count-- && (ret == -EBUSY || ret == -ETIMEDOUT)) {
 		queue_delayed_work(con->wq, &uwork->work, uwork->delay);
-	else
+	} else {
+		list_del(&uwork->node);
 		kfree(uwork);
+	}
 
 	mutex_unlock(&con->lock);
 }
@@ -236,6 +240,7 @@ static int ucsi_partner_task(struct ucsi_connector *con,
 	uwork->con = con;
 	uwork->cb = cb;
 
+	list_add_tail(&uwork->node, &con->partner_tasks);
 	queue_delayed_work(con->wq, &uwork->work, delay);
 
 	return 0;
@@ -1056,6 +1061,7 @@ static int ucsi_register_port(struct ucsi *ucsi, int index)
 	INIT_WORK(&con->work, ucsi_handle_connector_change);
 	init_completion(&con->complete);
 	mutex_init(&con->lock);
+	INIT_LIST_HEAD(&con->partner_tasks);
 	con->num = index + 1;
 	con->ucsi = ucsi;
 
@@ -1420,8 +1426,20 @@ void ucsi_unregister(struct ucsi *ucsi)
 		ucsi_unregister_altmodes(&ucsi->connector[i],
 					 UCSI_RECIPIENT_CON);
 		ucsi_unregister_port_psy(&ucsi->connector[i]);
-		if (ucsi->connector[i].wq)
+
+		if (ucsi->connector[i].wq) {
+			struct ucsi_work *uwork;
+
+			mutex_lock(&ucsi->connector[i].lock);
+			/*
+			 * queue delayed items immediately so they can execute
+			 * and free themselves before the wq is destroyed
+			 */
+			list_for_each_entry(uwork, &ucsi->connector[i].partner_tasks, node)
+				mod_delayed_work(ucsi->connector[i].wq, &uwork->work, 0);
+			mutex_unlock(&ucsi->connector[i].lock);
 			destroy_workqueue(ucsi->connector[i].wq);
+		}
 		typec_unregister_port(ucsi->connector[i].port);
 	}
 
diff --git a/drivers/usb/typec/ucsi/ucsi.h b/drivers/usb/typec/ucsi/ucsi.h
index c968474ee547..60ce9fb6e745 100644
--- a/drivers/usb/typec/ucsi/ucsi.h
+++ b/drivers/usb/typec/ucsi/ucsi.h
@@ -322,6 +322,7 @@ struct ucsi_connector {
 	struct work_struct work;
 	struct completion complete;
 	struct workqueue_struct *wq;
+	struct list_head partner_tasks;
 
 	struct typec_port *port;
 	struct typec_partner *partner;
-- 
2.24.0