On Tue, Jun 12, 2018 at 09:53:01AM +0800, Peter Chen wrote:
> 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@xxxxxxxxxxxxxxx>
> Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
> Cc: Jun Li <jun.li@xxxxxxx>
> Signed-off-by: Peter Chen <peter.chen@xxxxxxx>
Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> ---
> 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 0ccd2ce1eb59..2ed07d0bf364 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");
Thanks,
--
heikki
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