On Tue, Apr 23, 2024 at 08:23:57PM +0000, RD Babiera wrote:
> 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.
I'm probable missing something, but wouldn't it be safer to check
port->state after grabbing the lock?
> Fixes: 03eafcfb60c0 ("usb: typec: tcpm: Add tcpm_queue_vdm_unlocked() helper")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: RD Babiera <rdbabiera@xxxxxxxxxx>
> ---
> 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
--
heikki
