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

commit d5a4f93511b7000183c0d528739b824752139f79 upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
index ded49e3bf2b02506b34b8d0b4272f0eec1b8d9d4..9b29b67191bcf4bda445f6ffa02b5128b4166dc3 100644 (file)
--- a/drivers/usb/typec/tcpm.c
+++ b/drivers/usb/typec/tcpm.c
@@ -388,17 +388,18 @@ 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");