patch "usb: typec: tcpm: fix logbuffer index is wrong if _tcpm_log is" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb: typec: tcpm: fix logbuffer index is wrong if _tcpm_log is

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Peter Chen <[email protected]>
Date: Tue, 12 Jun 2018 09:53:01 +0800
Subject: 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

---
 drivers/usb/typec/tcpm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

index 0dfd755020f4..d961f1ec0e08 100644
@@ -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");

2.18.0