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Message-ID: <CAPTae5JNVj5ayJNbsH9YQLoJ+3pWPde7ZdeJMVa7HKpHFg+syQ@mail.gmail.com>
Date: Tue, 6 May 2025 15:28:05 -0700
From: Badhri Jagan Sridharan <badhri@...gle.com>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc: RD Babiera <rdbabiera@...gle.com>, gregkh@...uxfoundation.org,
linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH v1] usb: typec: tcpm: move tcpm_queue_vdm_unlocked to
asynchronous work
On Tue, May 6, 2025 at 4:27 AM Heikki Krogerus
<heikki.krogerus@...ux.intel.com> wrote:
>
> On Tue, Apr 29, 2025 at 11:49:08PM +0000, RD Babiera wrote:
> > 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.
Hi RD,
The patch looks good to me.
Lets also add the callstack of the different threads for reference.
Thanks,
Badhri
> >
> > Fixes: cdc9946ea637 ("usb: typec: tcpm: enforce ready state when queueing alt mode vdm")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: RD Babiera <rdbabiera@...gle.com>
>
> Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.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
>
> --
> heikki
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