Re: [PATCH v2] usb: stkwebcam: update the reference count of the usb device structure
From: Hans Verkuil <hidden>
Date: 2021-09-01 10:55:39
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Hi Salah, Cai, I received patches for this from both of you, but both have issues: On 31/07/2021 18:18, Salah Triki wrote:
quoted hunk ↗ jump to hunk
Use usb_get_dev() to increment the reference count of the usb device structure in order to avoid releasing the structure while it is still in use. And use usb_put_dev() to decrement the reference count and thus, when it will be equal to 0 the structure will be released. Signed-off-by: Salah Triki <salah.triki@gmail.com> --- Change since v1: Modification of the description drivers/media/usb/stkwebcam/stk-webcam.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/drivers/media/usb/stkwebcam/stk-webcam.c b/drivers/media/usb/stkwebcam/stk-webcam.c index a45d464427c4..3b14679829ed 100644 --- a/drivers/media/usb/stkwebcam/stk-webcam.c +++ b/drivers/media/usb/stkwebcam/stk-webcam.c@@ -1309,7 +1309,7 @@ static int stk_camera_probe(struct usb_interface *interface, init_waitqueue_head(&dev->wait_frame); dev->first_init = 1; /* webcam LED management */ - dev->udev = udev; + dev->udev = usb_get_dev(udev); dev->interface = interface; usb_get_intf(interface);
In the error path of stk_camera_probe you need to call usb_put_dev(), otherwise the udev refcount won't go to 0.
quoted hunk ↗ jump to hunk
@@ -1376,6 +1376,7 @@ static void stk_camera_disconnect(struct usb_interface *interface) usb_set_intfdata(interface, NULL); unset_present(dev); + usb_put_dev(interface_to_usbdev(interface));
Cai just used usb_put_dev(dev->udev) here which makes more sense.
Cai also moved this to the stk_v4l_dev_release() function, which is probably
a better place.
However, there is another bug here as well: these lines in stk_camera_disconnect()
should be moved to stk_v4l_dev_release():
v4l2_ctrl_handler_free(&dev->hdl);
v4l2_device_unregister(&dev->v4l2_dev);
kfree(dev);
When the last user of the video device has closed their fh, then stk_v4l_dev_release()
is called, so any cleanup of resources/memory should happen there. Right now if you are
streaming and the webcam is disconnected (or the device forcibly unloaded), the dev
pointer is freed in disconnect, but stk_v4l_dev_release() is called later and will
reference freed memory.
I'm not sure who of the two of you will make a v3, I leave that to you to fight out :-)
Regards,
Hans
wake_up_interruptible(&dev->wait_frame);