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Date: Tue, 23 Apr 2024 20:23:57 +0000
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Message-ID: <20240423202356.3372314-2-rdbabiera@google.com>
Subject: [PATCH v1] usb: typec: tcpm: enforce ready state when queueing alt
 mode vdm
From: RD Babiera <rdbabiera@google.com>
To: linux@roeck-us.net, heikki.krogerus@linux.intel.com, 
	gregkh@linuxfoundation.org, hdegoede@redhat.com
Cc: badhri@google.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, 
	RD Babiera <rdbabiera@google.com>, stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

Before sending Enter Mode for an Alt Mode, there is a gap between Discover
Modes and the Alt Mode driver queueing the Enter Mode VDM for the port
partner to send a message to the port.

If this message results in unregistering Alt Modes such as in a DR_SWAP,
then the following deadlock can occur with respect to the DisplayPort Alt
Mode driver:
1. The DR_SWAP state holds port->lock. Unregistering the Alt Mode driver
results in a cancel_work_sync() that waits for the current dp_altmode_work
to finish.
2. dp_altmode_work makes a call to tcpm_altmode_enter. The deadlock occurs
because tcpm_queue_vdm_unlock attempts to hold port->lock.

Before attempting to grab the lock, ensure that the port is in a state
vdm_run_state_machine can run in. Alt Mode unregistration will not occur
in these states.

Fixes: 03eafcfb60c0 ("usb: typec: tcpm: Add tcpm_queue_vdm_unlocked() helper")
Cc: stable@vger.kernel.org
Signed-off-by: RD Babiera <rdbabiera@google.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index c26fb70c3ec6..6fa1601ac259 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -1564,6 +1564,10 @@ static void tcpm_queue_vdm(struct tcpm_port *port, const u32 header,
 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)
 {
+	if (port->state != SRC_READY && port->state != SNK_READY &&
+	    port->state != SRC_VDM_IDENTITY_REQUEST)
+		return;
+
 	mutex_lock(&port->lock);
 	tcpm_queue_vdm(port, header, data, cnt, TCPC_TX_SOP);
 	mutex_unlock(&port->lock);

base-commit: 684e9f5f97eb4b7831298ffad140d5c1d426ff27
-- 
2.44.0.769.g3c40516874-goog