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Commit 6ab67054 authored by Ricardo Ribalda's avatar Ricardo Ribalda Committed by Greg Kroah-Hartman
Browse files

media: uvcvideo: Fix race condition with usb_kill_urb 



commit 619d9b710cf06f7a00a17120ca92333684ac45a8 upstream.

usb_kill_urb warranties that all the handlers are finished when it
returns, but does not protect against threads that might be handling
asynchronously the urb.

For UVC, the function uvc_ctrl_status_event_async() takes care of
control changes asynchronously.

If the code is executed in the following order:

CPU 0					CPU 1
===== 					=====
uvc_status_complete()
					uvc_status_stop()
uvc_ctrl_status_event_work()
					uvc_status_start() -> FAIL

Then uvc_status_start will keep failing and this error will be shown:

<4>[    5.540139] URB 0000000000000000 submitted while active
drivers/usb/core/urb.c:378 usb_submit_urb+0x4c3/0x528

Let's improve the current situation, by not re-submiting the urb if
we are stopping the status event. Also process the queued work
(if any) during stop.

CPU 0					CPU 1
===== 					=====
uvc_status_complete()
					uvc_status_stop()
					uvc_status_start()
uvc_ctrl_status_event_work() -> FAIL

Hopefully, with the usb layer protection this should be enough to cover
all the cases.

Cc: stable@vger.kernel.org
Fixes: e5225c82 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
Reviewed-by: default avatarYunke Cao <yunkec@chromium.org>
Signed-off-by: default avatarRicardo Ribalda <ribalda@chromium.org>
Reviewed-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0b8962c6

drivers/media/usb/uvc/uvc_ctrl.c

+5 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
 *          Laurent Pinchart (laurent.pinchart@ideasonboard.com)

 */



#include <asm/barrier.h>

#include <linux/kernel.h>

#include <linux/list.h>

#include <linux/module.h>
@@ -1318,6 +1319,10 @@ static void uvc_ctrl_status_event_work(struct work_struct *work) 


	uvc_ctrl_status_event(w->chain, w->ctrl, w->data);



	/* The barrier is needed to synchronize with uvc_status_stop(). */

	if (smp_load_acquire(&dev->flush_status))

		return;



	/* Resubmit the URB. */

	w->urb->interval = dev->int_ep->desc.bInterval;

	ret = usb_submit_urb(w->urb, GFP_KERNEL);

drivers/media/usb/uvc/uvc_status.c

+37 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
 *          Laurent Pinchart (laurent.pinchart@ideasonboard.com)

 */



#include <asm/barrier.h>

#include <linux/kernel.h>

#include <linux/input.h>

#include <linux/slab.h>
@@ -310,5 +311,41 @@ int uvc_status_start(struct uvc_device *dev, gfp_t flags) 


void uvc_status_stop(struct uvc_device *dev)

{

	struct uvc_ctrl_work *w = &dev->async_ctrl;



	/*

	 * Prevent the asynchronous control handler from requeing the URB. The

	 * barrier is needed so the flush_status change is visible to other

	 * CPUs running the asynchronous handler before usb_kill_urb() is

	 * called below.

	 */

	smp_store_release(&dev->flush_status, true);



	/*

	 * Cancel any pending asynchronous work. If any status event was queued,

	 * process it synchronously.

	 */

	if (cancel_work_sync(&w->work))

		uvc_ctrl_status_event(w->chain, w->ctrl, w->data);



	/* Kill the urb. */

	usb_kill_urb(dev->int_urb);



	/*

	 * The URB completion handler may have queued asynchronous work. This

	 * won't resubmit the URB as flush_status is set, but it needs to be

	 * cancelled before returning or it could then race with a future

	 * uvc_status_start() call.

	 */

	if (cancel_work_sync(&w->work))

		uvc_ctrl_status_event(w->chain, w->ctrl, w->data);



	/*

	 * From this point, there are no events on the queue and the status URB

	 * is dead. No events will be queued until uvc_status_start() is called.

	 * The barrier is needed to make sure that flush_status is visible to

	 * uvc_ctrl_status_event_work() when uvc_status_start() will be called

	 * again.

	 */

	smp_store_release(&dev->flush_status, false);

}

drivers/media/usb/uvc/uvcvideo.h

+1 −0
Original line number Diff line number Diff line
@@ -664,6 +664,7 @@ struct uvc_device { 
	/* Status Interrupt Endpoint */

	struct usb_host_endpoint *int_ep;

	struct urb *int_urb;

	bool flush_status;

	u8 *status;

	struct input_dev *input;

	char input_phys[64];