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 683617714e7cf852fdf3fc2d4ec8590ab6d1a114..58241ec1e91d7e0d5c40b9d5fcff0c15046cf45c 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -417,25 +417,33 @@ static void acm_read_bulk_callback(struct urb *urb)
        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);