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media: uvcvideo: Fix race condition with usb_kill_urb
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: e5225c820c
("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>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
This commit is contained in:
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3 changed files with 43 additions and 0 deletions
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@ -6,6 +6,7 @@
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* Laurent Pinchart (laurent.pinchart@ideasonboard.com)
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* Laurent Pinchart (laurent.pinchart@ideasonboard.com)
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*/
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*/
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#include <asm/barrier.h>
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#include <linux/bitops.h>
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#include <linux/bitops.h>
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#include <linux/kernel.h>
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#include <linux/kernel.h>
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#include <linux/list.h>
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#include <linux/list.h>
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@ -1571,6 +1572,10 @@ static void uvc_ctrl_status_event_work(struct work_struct *work)
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uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
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uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
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/* The barrier is needed to synchronize with uvc_status_stop(). */
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if (smp_load_acquire(&dev->flush_status))
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return;
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/* Resubmit the URB. */
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/* Resubmit the URB. */
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w->urb->interval = dev->int_ep->desc.bInterval;
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w->urb->interval = dev->int_ep->desc.bInterval;
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ret = usb_submit_urb(w->urb, GFP_KERNEL);
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ret = usb_submit_urb(w->urb, GFP_KERNEL);
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@ -6,6 +6,7 @@
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* Laurent Pinchart (laurent.pinchart@ideasonboard.com)
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* Laurent Pinchart (laurent.pinchart@ideasonboard.com)
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*/
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*/
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#include <asm/barrier.h>
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#include <linux/kernel.h>
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#include <linux/kernel.h>
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#include <linux/input.h>
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#include <linux/input.h>
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#include <linux/slab.h>
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#include <linux/slab.h>
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@ -311,5 +312,41 @@ int uvc_status_start(struct uvc_device *dev, gfp_t flags)
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void uvc_status_stop(struct uvc_device *dev)
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void uvc_status_stop(struct uvc_device *dev)
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{
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{
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struct uvc_ctrl_work *w = &dev->async_ctrl;
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/*
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* Prevent the asynchronous control handler from requeing the URB. The
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* barrier is needed so the flush_status change is visible to other
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* CPUs running the asynchronous handler before usb_kill_urb() is
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* called below.
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*/
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smp_store_release(&dev->flush_status, true);
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/*
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* Cancel any pending asynchronous work. If any status event was queued,
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* process it synchronously.
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*/
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if (cancel_work_sync(&w->work))
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uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
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/* Kill the urb. */
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usb_kill_urb(dev->int_urb);
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usb_kill_urb(dev->int_urb);
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/*
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* The URB completion handler may have queued asynchronous work. This
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* won't resubmit the URB as flush_status is set, but it needs to be
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* cancelled before returning or it could then race with a future
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* uvc_status_start() call.
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*/
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if (cancel_work_sync(&w->work))
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uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
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/*
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* From this point, there are no events on the queue and the status URB
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* is dead. No events will be queued until uvc_status_start() is called.
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* The barrier is needed to make sure that flush_status is visible to
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* uvc_ctrl_status_event_work() when uvc_status_start() will be called
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* again.
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*/
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smp_store_release(&dev->flush_status, false);
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}
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}
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@ -577,6 +577,7 @@ struct uvc_device {
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struct usb_host_endpoint *int_ep;
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struct usb_host_endpoint *int_ep;
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struct urb *int_urb;
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struct urb *int_urb;
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struct uvc_status *status;
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struct uvc_status *status;
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bool flush_status;
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struct input_dev *input;
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struct input_dev *input;
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char input_phys[64];
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char input_phys[64];
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