linux-kernel - [PATCH v2 2/3] usb: typec: ucsi: Move unregister out of atomic section

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Message-ID: <20240819-pmic-glink-v6-11-races-v2-2-88fe3ab1f0e2@quicinc.com>
Date: Mon, 19 Aug 2024 13:07:46 -0700
From: Bjorn Andersson <quic_bjorande@...cinc.com>
To: Sebastian Reichel <sre@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        "Heikki
 Krogerus" <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>,
        Neil Armstrong <neil.armstrong@...aro.org>
CC: Johan Hovold <johan+linaro@...nel.org>, Chris Lew <quic_clew@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Stephen Boyd
	<swboyd@...omium.org>,
        Amit Pundir <amit.pundir@...aro.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>,
        Bjorn Andersson
	<quic_bjorande@...cinc.com>, <stable@...r.kernel.org>
Subject: [PATCH v2 2/3] usb: typec: ucsi: Move unregister out of atomic
 section

Commit '635ce0db8956 ("soc: qcom: pmic_glink: don't traverse clients
list without a lock")' moved the pmic_glink client list under a
spinlock, as it is accessed by the rpmsg/glink callback, which in turn
is invoked from IRQ context.

This means that ucsi_unregister() is now called from IRQ context, which
isn't feasible as it's expecting a sleepable context. An effort is under
way to get GLINK to invoke its callbacks in a sleepable context, but
until then lets schedule the unregistration.

A side effect of this is that ucsi_unregister() can now happen
after the remote processor, and thereby the communication link with it, is
gone. pmic_glink_send() is amended with a check to avoid the resulting NULL
pointer dereference.
This does however result in the user being informed about this error by
the following entry in the kernel log:

  ucsi_glink.pmic_glink_ucsi pmic_glink.ucsi.0: failed to send UCSI write request: -5

Fixes: 635ce0db8956 ("soc: qcom: pmic_glink: don't traverse clients list without a lock")
Cc: stable@...r.kernel.org
Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Tested-by: Amit Pundir <amit.pundir@...aro.org>
Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
---
 drivers/soc/qcom/pmic_glink.c       | 10 +++++++++-
 drivers/usb/typec/ucsi/ucsi_glink.c | 27 ++++++++++++++++++++++-----
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/drivers/soc/qcom/pmic_glink.c b/drivers/soc/qcom/pmic_glink.c
index 58ec91767d79..e4747f1d3da5 100644
--- a/drivers/soc/qcom/pmic_glink.c
+++ b/drivers/soc/qcom/pmic_glink.c
@@ -112,8 +112,16 @@ EXPORT_SYMBOL_GPL(pmic_glink_register_client);
 int pmic_glink_send(struct pmic_glink_client *client, void *data, size_t len)
 {
 	struct pmic_glink *pg = client->pg;
+	int ret;
 
-	return rpmsg_send(pg->ept, data, len);
+	mutex_lock(&pg->state_lock);
+	if (!pg->ept)
+		ret = -ECONNRESET;
+	else
+		ret = rpmsg_send(pg->ept, data, len);
+	mutex_unlock(&pg->state_lock);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(pmic_glink_send);
 
diff --git a/drivers/usb/typec/ucsi/ucsi_glink.c b/drivers/usb/typec/ucsi/ucsi_glink.c
index ac53a81c2a81..bb6244f21e0a 100644
--- a/drivers/usb/typec/ucsi/ucsi_glink.c
+++ b/drivers/usb/typec/ucsi/ucsi_glink.c
@@ -68,6 +68,9 @@ struct pmic_glink_ucsi {
 
 	struct work_struct notify_work;
 	struct work_struct register_work;
+	spinlock_t state_lock;
+	bool ucsi_registered;
+	bool pd_running;
 
 	u8 read_buf[UCSI_BUF_SIZE];
 };
@@ -244,8 +247,20 @@ static void pmic_glink_ucsi_notify(struct work_struct *work)
 static void pmic_glink_ucsi_register(struct work_struct *work)
 {
 	struct pmic_glink_ucsi *ucsi = container_of(work, struct pmic_glink_ucsi, register_work);
+	unsigned long flags;
+	bool pd_running;
 
-	ucsi_register(ucsi->ucsi);
+	spin_lock_irqsave(&ucsi->state_lock, flags);
+	pd_running = ucsi->pd_running;
+	spin_unlock_irqrestore(&ucsi->state_lock, flags);
+
+	if (!ucsi->ucsi_registered && pd_running) {
+		ucsi_register(ucsi->ucsi);
+		ucsi->ucsi_registered = true;
+	} else if (ucsi->ucsi_registered && !pd_running) {
+		ucsi_unregister(ucsi->ucsi);
+		ucsi->ucsi_registered = false;
+	}
 }
 
 static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
@@ -269,11 +284,12 @@ static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
 static void pmic_glink_ucsi_pdr_notify(void *priv, int state)
 {
 	struct pmic_glink_ucsi *ucsi = priv;
+	unsigned long flags;
 
-	if (state == SERVREG_SERVICE_STATE_UP)
-		schedule_work(&ucsi->register_work);
-	else if (state == SERVREG_SERVICE_STATE_DOWN)
-		ucsi_unregister(ucsi->ucsi);
+	spin_lock_irqsave(&ucsi->state_lock, flags);
+	ucsi->pd_running = state == SERVREG_SERVICE_STATE_UP;
+	spin_unlock_irqrestore(&ucsi->state_lock, flags);
+	schedule_work(&ucsi->register_work);
 }
 
 static void pmic_glink_ucsi_destroy(void *data)
@@ -320,6 +336,7 @@ static int pmic_glink_ucsi_probe(struct auxiliary_device *adev,
 	INIT_WORK(&ucsi->register_work, pmic_glink_ucsi_register);
 	init_completion(&ucsi->read_ack);
 	init_completion(&ucsi->write_ack);
+	spin_lock_init(&ucsi->state_lock);
 	mutex_init(&ucsi->lock);
 
 	ucsi->ucsi = ucsi_create(dev, &pmic_glink_ucsi_ops);

-- 
2.34.1