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: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives") Reviewed-by: Yunke Cao yunkec@chromium.org Signed-off-by: Ricardo Ribalda ribalda@chromium.org --- uvc: Fix race condition on uvc
Make sure that all the async work is finished when we stop the status urb.
To: Hillf Danton hdanton@sina.com To: Yunke Cao yunkec@chromium.org To: Sergey Senozhatsky senozhatsky@chromium.org To: Max Staudt mstaudt@google.com To: Laurent Pinchart laurent.pinchart@ideasonboard.com To: Mauro Carvalho Chehab mchehab@kernel.org Cc: linux-media@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- Changes in v7: - Use smp_store_release. (Thanks Hilf!) - Rebase on top of uvc/next. - Link to v6: https://lore.kernel.org/r/20221212-uvc-race-v6-0-2a662f8de011@chromium.org
Changes in v6: - Improve comments. (Thanks Laurent). - Use true/false instead of 1/0 (Thanks Laurent). - Link to v5: https://lore.kernel.org/r/20221212-uvc-race-v5-0-3db3933d1608@chromium.org
Changes in v5: - atomic_t do not impose barriers, use smp_mb() instead. (Thanks Laurent) - Add an extra cancel_work_sync(). - Link to v4: https://lore.kernel.org/r/20221212-uvc-race-v4-0-38d7075b03f5@chromium.org
Changes in v4: - Replace bool with atomic_t to avoid compiler reordering. - First complete the async work and then kill the urb to avoid race (Thanks Laurent!) - Link to v3: https://lore.kernel.org/r/20221212-uvc-race-v3-0-954efc752c9a@chromium.org
Changes in v3: - Remove the patch for dev->status, makes more sense in another series, and makes the zero day less nervous. - Update reviewed-by (thanks Yunke!). - Link to v2: https://lore.kernel.org/r/20221212-uvc-race-v2-0-54496cc3b8ab@chromium.org
Changes in v2: - Add a patch for not kalloc dev->status - Redo the logic mechanism, so it also works with suspend (Thanks Yunke!) - Link to v1: https://lore.kernel.org/r/20221212-uvc-race-v1-0-c52e1783c31d@chromium.org --- drivers/media/usb/uvc/uvc_ctrl.c | 5 +++++ drivers/media/usb/uvc/uvc_status.c | 33 +++++++++++++++++++++++++++++++++ drivers/media/usb/uvc/uvcvideo.h | 1 + 3 files changed, 39 insertions(+)
diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c index e07b56bbf853..30c417768376 100644 --- a/drivers/media/usb/uvc/uvc_ctrl.c +++ b/drivers/media/usb/uvc/uvc_ctrl.c @@ -6,6 +6,7 @@ * Laurent Pinchart (laurent.pinchart@ideasonboard.com) */
+#include <asm/barrier.h> #include <linux/bitops.h> #include <linux/kernel.h> #include <linux/list.h> @@ -1509,6 +1510,10 @@ 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); diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c index 602830a8023e..21e13b8441da 100644 --- a/drivers/media/usb/uvc/uvc_status.c +++ b/drivers/media/usb/uvc/uvc_status.c @@ -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> @@ -311,5 +312,37 @@ 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); + + /* If there is any status event on the queue, process it. */ + 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, this is, no events will be queued until uvc_status_start() + * is called. The barrier is needed to make sure that it is written to + * memory before uvc_status_start() is called again. + */ + smp_store_release(&dev->flush_status, false); } diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h index ae0066eceffd..b2b277cccbdb 100644 --- a/drivers/media/usb/uvc/uvcvideo.h +++ b/drivers/media/usb/uvc/uvcvideo.h @@ -578,6 +578,7 @@ struct uvc_device { struct usb_host_endpoint *int_ep; struct urb *int_urb; struct uvc_status *status; + bool flush_status;
struct input_dev *input; char input_phys[64];
--- base-commit: fb1316b0ff3fc3cd98637040ee17ab7be753aac7 change-id: 20221212-uvc-race-09276ea68bf8
Best regards,