Hi Ricardo,
Thank you for the patch.
On Thu, Jan 05, 2023 at 03:31:29PM +0100, Ricardo Ribalda wrote:
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.
For some reason the word "hopefully" in a bug fix doesn't make me very hopeful ;-)
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. */
/* * 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, 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.
With data races, the concept of "written to memory" doesn't make much sense anymore.
* 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.
I'll update the comments locally.
Reviewed-by: Laurent Pinchart laurent.pinchart@ideasonboard.com
*/- 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