usb: typec: tcpm: fix logbuffer index is wrong if _tcpm_log is re-entered

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>

diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
index 0dfd755020f43f3b91a23b7cd430fd7c753dd09c..d961f1ec0e0856a34f5c5e4ca87a2030549ac960 100644 (file)
--- 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");