[PATCH v1] usb: typec: tcpm: move tcpm_queue_vdm_unlocked to asynchronous work

[RD Babiera <rdbabiera@google.com>]

A state check was previously added to tcpm_queue_vdm_unlocked to
prevent a deadlock where the DisplayPort Alt Mode driver would be
executing work and attempting to grab the tcpm_lock while the TCPM
was holding the lock and attempting to unregister the altmode, blocking
on the altmode driver's cancel_work_sync call.

Because the state check isn't protected, there is a small window
where the Alt Mode driver could determine that the TCPM is
in a ready state and attempt to grab the lock while the
TCPM grabs the lock and changes the TCPM state to one that
causes the deadlock.

Change tcpm_queue_vdm_unlocked to queue for tcpm_queue_vdm_work,
which can perform the state check while holding the TCPM lock
while the Alt Mode lock is no longer held. This requires a new
struct to hold the vdm data, altmode_vdm_event.

Fixes: cdc9946ea637 ("usb: typec: tcpm: enforce ready state when queueing alt mode vdm")
Cc: stable@vger.kernel.org
Signed-off-by: RD Babiera <rdbabiera@google.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 91 +++++++++++++++++++++++++++--------
 1 file changed, 71 insertions(+), 20 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 784fa23102f9..9b8d98328ddb 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -597,6 +597,15 @@ struct pd_rx_event {
 	enum tcpm_transmit_type rx_sop_type;
 };
 
+struct altmode_vdm_event {
+	struct kthread_work work;
+	struct tcpm_port *port;
+	u32 header;
+	u32 *data;
+	int cnt;
+	enum tcpm_transmit_type tx_sop_type;
+};
+
 static const char * const pd_rev[] = {
 	[PD_REV10]		= "rev1",
 	[PD_REV20]		= "rev2",
@@ -1610,18 +1619,68 @@ static void tcpm_queue_vdm(struct tcpm_port *port, const u32 header,
 	mod_vdm_delayed_work(port, 0);
 }
 
-static void tcpm_queue_vdm_unlocked(struct tcpm_port *port, const u32 header,
-				    const u32 *data, int cnt, enum tcpm_transmit_type tx_sop_type)
+static void tcpm_queue_vdm_work(struct kthread_work *work)
 {
-	if (port->state != SRC_READY && port->state != SNK_READY &&
-	    port->state != SRC_VDM_IDENTITY_REQUEST)
-		return;
+	struct altmode_vdm_event *event = container_of(work,
+						       struct altmode_vdm_event,
+						       work);
+	struct tcpm_port *port = event->port;
 
 	mutex_lock(&port->lock);
-	tcpm_queue_vdm(port, header, data, cnt, tx_sop_type);
+	if (port->state != SRC_READY && port->state != SNK_READY &&
+	    port->state != SRC_VDM_IDENTITY_REQUEST) {
+		tcpm_log_force(port, "dropping altmode_vdm_event");
+		goto port_unlock;
+	}
+
+	tcpm_queue_vdm(port, event->header, event->data, event->cnt, event->tx_sop_type);
+
+port_unlock:
+	kfree(event->data);
+	kfree(event);
 	mutex_unlock(&port->lock);
 }
 
+static int tcpm_queue_vdm_unlocked(struct tcpm_port *port, const u32 header,
+				   const u32 *data, int cnt, enum tcpm_transmit_type tx_sop_type)
+{
+	struct altmode_vdm_event *event;
+	u32 *data_cpy;
+	int ret = -ENOMEM;
+
+	event = kzalloc(sizeof(*event), GFP_KERNEL);
+	if (!event)
+		goto err_event;
+
+	data_cpy = kcalloc(cnt, sizeof(u32), GFP_KERNEL);
+	if (!data_cpy)
+		goto err_data;
+
+	kthread_init_work(&event->work, tcpm_queue_vdm_work);
+	event->port = port;
+	event->header = header;
+	memcpy(data_cpy, data, sizeof(u32) * cnt);
+	event->data = data_cpy;
+	event->cnt = cnt;
+	event->tx_sop_type = tx_sop_type;
+
+	ret = kthread_queue_work(port->wq, &event->work);
+	if (!ret) {
+		ret = -EBUSY;
+		goto err_queue;
+	}
+
+	return 0;
+
+err_queue:
+	kfree(data_cpy);
+err_data:
+	kfree(event);
+err_event:
+	tcpm_log_force(port, "failed to queue altmode vdm, err:%d", ret);
+	return ret;
+}
+
 static void svdm_consume_identity(struct tcpm_port *port, const u32 *p, int cnt)
 {
 	u32 vdo = p[VDO_INDEX_IDH];
@@ -2832,8 +2891,7 @@ static int tcpm_altmode_enter(struct typec_altmode *altmode, u32 *vdo)
 	header = VDO(altmode->svid, vdo ? 2 : 1, svdm_version, CMD_ENTER_MODE);
 	header |= VDO_OPOS(altmode->mode);
 
-	tcpm_queue_vdm_unlocked(port, header, vdo, vdo ? 1 : 0, TCPC_TX_SOP);
-	return 0;
+	return tcpm_queue_vdm_unlocked(port, header, vdo, vdo ? 1 : 0, TCPC_TX_SOP);
 }
 
 static int tcpm_altmode_exit(struct typec_altmode *altmode)
@@ -2849,8 +2907,7 @@ static int tcpm_altmode_exit(struct typec_altmode *altmode)
 	header = VDO(altmode->svid, 1, svdm_version, CMD_EXIT_MODE);
 	header |= VDO_OPOS(altmode->mode);
 
-	tcpm_queue_vdm_unlocked(port, header, NULL, 0, TCPC_TX_SOP);
-	return 0;
+	return tcpm_queue_vdm_unlocked(port, header, NULL, 0, TCPC_TX_SOP);
 }
 
 static int tcpm_altmode_vdm(struct typec_altmode *altmode,
@@ -2858,9 +2915,7 @@ static int tcpm_altmode_vdm(struct typec_altmode *altmode,
 {
 	struct tcpm_port *port = typec_altmode_get_drvdata(altmode);
 
-	tcpm_queue_vdm_unlocked(port, header, data, count - 1, TCPC_TX_SOP);
-
-	return 0;
+	return tcpm_queue_vdm_unlocked(port, header, data, count - 1, TCPC_TX_SOP);
 }
 
 static const struct typec_altmode_ops tcpm_altmode_ops = {
@@ -2884,8 +2939,7 @@ static int tcpm_cable_altmode_enter(struct typec_altmode *altmode, enum typec_pl
 	header = VDO(altmode->svid, vdo ? 2 : 1, svdm_version, CMD_ENTER_MODE);
 	header |= VDO_OPOS(altmode->mode);
 
-	tcpm_queue_vdm_unlocked(port, header, vdo, vdo ? 1 : 0, TCPC_TX_SOP_PRIME);
-	return 0;
+	return tcpm_queue_vdm_unlocked(port, header, vdo, vdo ? 1 : 0, TCPC_TX_SOP_PRIME);
 }
 
 static int tcpm_cable_altmode_exit(struct typec_altmode *altmode, enum typec_plug_index sop)
@@ -2901,8 +2955,7 @@ static int tcpm_cable_altmode_exit(struct typec_altmode *altmode, enum typec_plu
 	header = VDO(altmode->svid, 1, svdm_version, CMD_EXIT_MODE);
 	header |= VDO_OPOS(altmode->mode);
 
-	tcpm_queue_vdm_unlocked(port, header, NULL, 0, TCPC_TX_SOP_PRIME);
-	return 0;
+	return tcpm_queue_vdm_unlocked(port, header, NULL, 0, TCPC_TX_SOP_PRIME);
 }
 
 static int tcpm_cable_altmode_vdm(struct typec_altmode *altmode, enum typec_plug_index sop,
@@ -2910,9 +2963,7 @@ static int tcpm_cable_altmode_vdm(struct typec_altmode *altmode, enum typec_plug
 {
 	struct tcpm_port *port = typec_altmode_get_drvdata(altmode);
 
-	tcpm_queue_vdm_unlocked(port, header, data, count - 1, TCPC_TX_SOP_PRIME);
-
-	return 0;
+	return tcpm_queue_vdm_unlocked(port, header, data, count - 1, TCPC_TX_SOP_PRIME);
 }
 
 static const struct typec_cable_ops tcpm_cable_ops = {

base-commit: 615dca38c2eae55aff80050275931c87a812b48c
-- 
2.49.0.967.g6a0df3ecc3-goog