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Message-ID: <aA-BTrunTaYxtrps@kuha.fi.intel.com>
Date: Mon, 28 Apr 2025 16:23:26 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Andrei Kuchynski <akuchynski@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jameson Thies <jthies@...gle.com>,
Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
Benson Leung <bleung@...omium.org>,
Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>,
Pooja Katiyar <pooja.katiyar@...el.com>,
Madhu M <madhu.m@...el.com>, linux-usb@...r.kernel.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] usb: typec: ucsi: displayport: Fix deadlock
On Thu, Apr 24, 2025 at 08:44:28AM +0000, Andrei Kuchynski wrote:
> This patch introduces the ucsi_con_mutex_lock / ucsi_con_mutex_unlock
> functions to the UCSI driver. ucsi_con_mutex_lock ensures the connector
> mutex is only locked if a connection is established and the partner pointer
> is valid. This resolves a deadlock scenario where
> ucsi_displayport_remove_partner holds con->mutex waiting for
> dp_altmode_work to complete while dp_altmode_work attempts to acquire it.
>
> Cc: stable@...r.kernel.org
> Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
> Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> ---
> drivers/usb/typec/ucsi/displayport.c | 19 +++++++++-------
> drivers/usb/typec/ucsi/ucsi.c | 34 ++++++++++++++++++++++++++++
> drivers/usb/typec/ucsi/ucsi.h | 2 ++
> 3 files changed, 47 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> index 420af5139c70..acd053d4e38c 100644
> --- a/drivers/usb/typec/ucsi/displayport.c
> +++ b/drivers/usb/typec/ucsi/displayport.c
> @@ -54,7 +54,8 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
> u8 cur = 0;
> int ret;
>
> - mutex_lock(&dp->con->lock);
> + if (!ucsi_con_mutex_lock(dp->con))
> + return -ENOTCONN;
>
> if (!dp->override && dp->initialized) {
> const struct typec_altmode *p = typec_altmode_get_partner(alt);
> @@ -100,7 +101,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
> schedule_work(&dp->work);
> ret = 0;
> err_unlock:
> - mutex_unlock(&dp->con->lock);
> + ucsi_con_mutex_unlock(dp->con);
>
> return ret;
> }
> @@ -112,7 +113,8 @@ static int ucsi_displayport_exit(struct typec_altmode *alt)
> u64 command;
> int ret = 0;
>
> - mutex_lock(&dp->con->lock);
> + if (!ucsi_con_mutex_lock(dp->con))
> + return -ENOTCONN;
>
> if (!dp->override) {
> const struct typec_altmode *p = typec_altmode_get_partner(alt);
> @@ -144,7 +146,7 @@ static int ucsi_displayport_exit(struct typec_altmode *alt)
> schedule_work(&dp->work);
>
> out_unlock:
> - mutex_unlock(&dp->con->lock);
> + ucsi_con_mutex_unlock(dp->con);
>
> return ret;
> }
> @@ -202,20 +204,21 @@ static int ucsi_displayport_vdm(struct typec_altmode *alt,
> int cmd = PD_VDO_CMD(header);
> int svdm_version;
>
> - mutex_lock(&dp->con->lock);
> + if (!ucsi_con_mutex_lock(dp->con))
> + return -ENOTCONN;
>
> if (!dp->override && dp->initialized) {
> const struct typec_altmode *p = typec_altmode_get_partner(alt);
>
> dev_warn(&p->dev,
> "firmware doesn't support alternate mode overriding\n");
> - mutex_unlock(&dp->con->lock);
> + ucsi_con_mutex_unlock(dp->con);
> return -EOPNOTSUPP;
> }
>
> svdm_version = typec_altmode_get_svdm_version(alt);
> if (svdm_version < 0) {
> - mutex_unlock(&dp->con->lock);
> + ucsi_con_mutex_unlock(dp->con);
> return svdm_version;
> }
>
> @@ -259,7 +262,7 @@ static int ucsi_displayport_vdm(struct typec_altmode *alt,
> break;
> }
>
> - mutex_unlock(&dp->con->lock);
> + ucsi_con_mutex_unlock(dp->con);
>
> return 0;
> }
> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
> index e8c7e9dc4930..01ce858a1a2b 100644
> --- a/drivers/usb/typec/ucsi/ucsi.c
> +++ b/drivers/usb/typec/ucsi/ucsi.c
> @@ -1922,6 +1922,40 @@ void ucsi_set_drvdata(struct ucsi *ucsi, void *data)
> }
> EXPORT_SYMBOL_GPL(ucsi_set_drvdata);
>
> +/**
> + * ucsi_con_mutex_lock - Acquire the connector mutex
> + * @con: The connector interface to lock
> + *
> + * Returns true on success, false if the connector is disconnected
> + */
> +bool ucsi_con_mutex_lock(struct ucsi_connector *con)
> +{
> + bool mutex_locked = false;
> + bool connected = true;
> +
> + while (connected && !mutex_locked) {
> + mutex_locked = mutex_trylock(&con->lock) != 0;
> + connected = UCSI_CONSTAT(con, CONNECTED);
> + if (connected && !mutex_locked)
> + msleep(20);
> + }
> +
> + connected = connected && con->partner;
> + if (!connected && mutex_locked)
> + mutex_unlock(&con->lock);
> +
> + return connected;
> +}
> +
> +/**
> + * ucsi_con_mutex_unlock - Release the connector mutex
> + * @con: The connector interface to unlock
> + */
> +void ucsi_con_mutex_unlock(struct ucsi_connector *con)
> +{
> + mutex_unlock(&con->lock);
> +}
> +
> /**
> * ucsi_create - Allocate UCSI instance
> * @dev: Device interface to the PPM (Platform Policy Manager)
> diff --git a/drivers/usb/typec/ucsi/ucsi.h b/drivers/usb/typec/ucsi/ucsi.h
> index 3a2c1762bec1..9c5278a0c5d4 100644
> --- a/drivers/usb/typec/ucsi/ucsi.h
> +++ b/drivers/usb/typec/ucsi/ucsi.h
> @@ -94,6 +94,8 @@ int ucsi_register(struct ucsi *ucsi);
> void ucsi_unregister(struct ucsi *ucsi);
> void *ucsi_get_drvdata(struct ucsi *ucsi);
> void ucsi_set_drvdata(struct ucsi *ucsi, void *data);
> +bool ucsi_con_mutex_lock(struct ucsi_connector *con);
> +void ucsi_con_mutex_unlock(struct ucsi_connector *con);
>
> void ucsi_connector_change(struct ucsi *ucsi, u8 num);
>
> --
> 2.49.0.805.g082f7c87e0-goog
--
heikki
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