From d5a4f93511b7000183c0d528739b824752139f79 Mon Sep 17 00:00:00 2001
From: Peter Chen <peter.chen@nxp.com>
Date: Tue, 12 Jun 2018 09:53:01 +0800
Subject: [PATCH] usb: typec: tcpm: fix logbuffer index is wrong if _tcpm_log
 is re-entered
Git-commit: d5a4f93511b7000183c0d528739b824752139f79
References: FATE#326325
Patch-mainline: v4.18

The port->logbuffer_head may be wrong if the two processes enters
_tcpm_log at the mostly same time. The 2nd process enters _tcpm_log
before the 1st process update the index, then the 2nd process will
not allocate logbuffer, when the 2nd process tries to use log buffer,
the index has already updated by the 1st process, so it will get
NULL pointer for updated logbuffer, the error message like below:

	tcpci 0-0050: Log buffer index 6 is NULL

Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Jun Li <jun.li@nxp.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/typec/tcpm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
index 0dfd755020f4..d961f1ec0e08 100644
--- a/drivers/usb/typec/tcpm.c
+++ b/drivers/usb/typec/tcpm.c
@@ -418,17 +418,18 @@ static void _tcpm_log(struct tcpm_port *port, const char *fmt, va_list args)
 	u64 ts_nsec = local_clock();
 	unsigned long rem_nsec;
 
+	mutex_lock(&port->logbuffer_lock);
 	if (!port->logbuffer[port->logbuffer_head]) {
 		port->logbuffer[port->logbuffer_head] =
 				kzalloc(LOG_BUFFER_ENTRY_SIZE, GFP_KERNEL);
-		if (!port->logbuffer[port->logbuffer_head])
+		if (!port->logbuffer[port->logbuffer_head]) {
+			mutex_unlock(&port->logbuffer_lock);
 			return;
+		}
 	}
 
 	vsnprintf(tmpbuffer, sizeof(tmpbuffer), fmt, args);
 
-	mutex_lock(&port->logbuffer_lock);
-
 	if (tcpm_log_full(port)) {
 		port->logbuffer_head = max(port->logbuffer_head - 1, 0);
 		strcpy(tmpbuffer, "overflow");
-- 
2.16.4