Re: [PATCH] usb: gadget: uvc: fix list double add in uvcg_video_pump

[Dan Vacura <w36195@motorola.com>]

Hi Laurent,

Thanks for the review!

On Fri, Jun 17, 2022 at 03:51:08PM +0300, Laurent Pinchart wrote:
> Hi Dan,
> 
> Thank you for the patch.
> 
> On Wed, Jun 15, 2022 at 10:09:15PM -0500, Dan Vacura wrote:
> > A panic can occur if the endpoint becomes disabled and the
> > uvcg_video_pump adds the request back to the req_free list after it has
> > already been queued to the endpoint. The endpoint complete will add the
> > request back to the req_free list. Invalidate the local request handle
> > once it's been queued.
> 
> Good catch !
> 
> > <6>[  246.796704][T13726] configfs-gadget gadget: uvc: uvc_function_set_alt(1, 0)
> > <3>[  246.797078][   T26] list_add double add: new=ffffff878bee5c40, prev=ffffff878bee5c40, next=ffffff878b0f0a90.
> > <6>[  246.797213][   T26] ------------[ cut here ]------------
> > <2>[  246.797224][   T26] kernel BUG at lib/list_debug.c:31!
> > <6>[  246.807073][   T26] Call trace:
> > <6>[  246.807180][   T26]  uvcg_video_pump+0x364/0x38c
> > <6>[  246.807366][   T26]  process_one_work+0x2a4/0x544
> > <6>[  246.807394][   T26]  worker_thread+0x350/0x784
> > <6>[  246.807442][   T26]  kthread+0x2ac/0x320
> > 
> > Fixes: f9897ec0f6d3 ("usb: gadget: uvc: only pump video data if necessary")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Dan Vacura <w36195@motorola.com>
> > ---
> >  drivers/usb/gadget/function/uvc_video.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> > index 93f42c7f800d..59e2f51b53a5 100644
> > --- a/drivers/usb/gadget/function/uvc_video.c
> > +++ b/drivers/usb/gadget/function/uvc_video.c
> > @@ -427,6 +427,9 @@ static void uvcg_video_pump(struct work_struct *work)
> >  		if (ret < 0) {
> >  			uvcg_queue_cancel(queue, 0);
> >  			break;
> > +		} else {
> > +			/* Endpoint now owns the request */
> > +			req = NULL;
> >  		}
> >  		video->req_int_count++;
> 
> I'd write it as
> 
> 		if (ret < 0) {
> 			uvcg_queue_cancel(queue, 0);
> 			break;
> 		}
> 
> 		/* Endpoint now owns the request. */
> 		req = NULL;
> 		video->req_int_count++;

This is cleaner. I'll send a v2 with this suggestion.

> 
> Apart from that,
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> >  	}
> 
> -- 
> Regards,
> 
> Laurent Pinchart