Re: [BUG] usb: typec: ucsi: possible deadlock in ucsi_pr_swap() and ucsi_handle_connector_change()

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

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On Wed, Feb 09, 2022 at 11:50:57AM +0800, Jia-Ju Bai wrote:
> Hello,
> 
> My static analysis tool reports a possible deadlock in the ucsi driver in
> Linux 5.16:
> 
> ucsi_pr_swap()
>   mutex_lock(&con->lock); --> Line 962 (Lock A)
>   wait_for_completion_timeout(&con->complete, ...) --> Line 981 (Wait X)
> 
> ucsi_handle_connector_change()
>   mutex_lock(&con->lock); --> Line 763 (Lock A)
>   complete(&con->complete); --> Line 782 (Wake X)
>   complete(&con->complete); --> Line 807 (Wake X)
> 
> When ucsi_pr_swap() is executed, "Wait X" is performed by holding "Lock A".
> If ucsi_handle_connector_change() is executed at this time, "Wake X" cannot
> be performed to wake up "Wait X" in ucsi_handle_connector_change(), because
> "Lock A" has been already held by ucsi_handle_connector_change(), causing a
> possible deadlock.
> I find that "Wait X" is performed with a timeout, to relieve the possible
> deadlock; but I think this timeout can cause inefficient execution.
> 
> I am not quite sure whether this possible problem is real.
> Any feedback would be appreciated, thanks :)

This is probable a regression from commit ad74b8649bea ("usb: typec:
ucsi: Preliminary support for alternate modes"). Can you test does
this patch fix the issue (attached)?

thanks,

-- 
heikki

[-- Attachment #2: 0001-usb-typec-ucsi-Test-fix.patch --]
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From 2ad06425a3df7be656f8a5b3c202aab45554fd17 Mon Sep 17 00:00:00 2001
From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Date: Wed, 9 Feb 2022 17:27:19 +0300
Subject: [PATCH] usb: typec: ucsi: Test fix

Interim.

Not-Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
---
 drivers/usb/typec/ucsi/ucsi.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
index f0c2fa19f3e0f..225104beda8be 100644
--- a/drivers/usb/typec/ucsi/ucsi.c
+++ b/drivers/usb/typec/ucsi/ucsi.c
@@ -956,14 +956,18 @@ static int ucsi_dr_swap(struct typec_port *port, enum typec_data_role role)
 	if (ret < 0)
 		goto out_unlock;
 
+	mutex_unlock(&con->lock);
+
 	if (!wait_for_completion_timeout(&con->complete,
 					msecs_to_jiffies(UCSI_SWAP_TIMEOUT_MS)))
-		ret = -ETIMEDOUT;
+		return -ETIMEDOUT;
+
+	return 0;
 
 out_unlock:
 	mutex_unlock(&con->lock);
 
-	return ret < 0 ? ret : 0;
+	return ret;
 }
 
 static int ucsi_pr_swap(struct typec_port *port, enum typec_role role)
@@ -992,11 +996,13 @@ static int ucsi_pr_swap(struct typec_port *port, enum typec_role role)
 	if (ret < 0)
 		goto out_unlock;
 
+	mutex_unlock(&con->lock);
+
 	if (!wait_for_completion_timeout(&con->complete,
-				msecs_to_jiffies(UCSI_SWAP_TIMEOUT_MS))) {
-		ret = -ETIMEDOUT;
-		goto out_unlock;
-	}
+				msecs_to_jiffies(UCSI_SWAP_TIMEOUT_MS)))
+		return -ETIMEDOUT;
+
+	mutex_lock(&con->lock);
 
 	/* Something has gone wrong while swapping the role */
 	if (UCSI_CONSTAT_PWR_OPMODE(con->status.flags) !=
@@ -1372,6 +1378,7 @@ void ucsi_unregister(struct ucsi *ucsi)
 	ucsi->ops->async_write(ucsi, UCSI_CONTROL, &cmd, sizeof(cmd));
 
 	for (i = 0; i < ucsi->cap.num_connectors; i++) {
+		complete(&ucsi->connector[i].complete);
 		cancel_work_sync(&ucsi->connector[i].work);
 		ucsi_unregister_partner(&ucsi->connector[i]);
 		ucsi_unregister_altmodes(&ucsi->connector[i],
-- 
2.34.1