cdc-acm: fix race between callback and unthrottle
Abn URB may be may marked free only after the buffer has been
processed or there is a small window during which it could
be submitted on another CPU and overwrite an unprocessed buffer
Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 6836177..58241ec 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -417,25 +417,33 @@
struct acm_rb *rb = urb->context;
struct acm *acm = rb->instance;
unsigned long flags;
+ int status = urb->status;
dev_vdbg(&acm->data->dev, "%s - urb %d, len %d\n", __func__,
rb->index, urb->actual_length);
- set_bit(rb->index, &acm->read_urbs_free);
if (!acm->dev) {
+ set_bit(rb->index, &acm->read_urbs_free);
dev_dbg(&acm->data->dev, "%s - disconnected\n", __func__);
return;
}
if (urb->status) {
+ set_bit(rb->index, &acm->read_urbs_free);
dev_dbg(&acm->data->dev, "%s - non-zero urb status: %d\n",
- __func__, urb->status);
+ __func__, status);
return;
}
usb_mark_last_busy(acm->dev);
acm_process_read_urb(acm, urb);
+ /*
+ * Unthrottle may run on another CPU which needs to see events
+ * in the same order. Submission has an implict barrier
+ */
+ smp_mb__before_atomic();
+ set_bit(rb->index, &acm->read_urbs_free);
/* throttle device if requested by tty */
spin_lock_irqsave(&acm->read_lock, flags);