Hi Paul, On Tuesday, 24 April 2018 23:59:33 EEST Paul Elder wrote: > Down the call stack from the ioctl handler for VIDIOC_STREAMON, > uvc_video_alloc_requests contains a BUG_ON, which in the high level, > triggers when VIDIOC_STREAMON ioctl is issued without VIDIOC_STREAMOFF > being issued previously. > > This can happen in a few ways, such as if the userspace uvc gadget > application simply doesn't issue VIDIOC_STREAMOFF. Another way is if > uvc_function_set_alt with alt 0 is called after it is called with 1 but > before VIDIOC_STREAMON is called; in this case, UVC_EVENT_STREAMOFF will > not be queued to userspace, and therefore userspace will never call > VIDIOC_STREAMOFF. > > To fix this, add two more uvc states: starting and stopping. The > starting state is entered when uvc_function_set_alt 1 is called, and is > exited in uvc_v4l2_streamon, when the state is changed to streaming. The > stopping state is entered when uvc_function_set_alt 0 is called, and is > exited in uvc_v4l2_streamoff, when the state is changed to connected. It would be useful to capture this in kerneldoc as a documentation of the states enum. I believe writing the description of state transitions down will also help you understand the potential race conditions. > The status phase of the SET_INTERFACE request doesn't need to be delayed > by the uvc gadget driver, so that is removed. > > Finally, there is another way to trigger the aforementioned BUG: start > streaming and (physically) disconnect usb. To fix this, call > uvcg_video_enable 0 in uvc_function_disable. > > Changes in v2: > 1. Remove delay usb status phase > > Paul Elder (3): > usb: gadget: uvc: synchronize streamon/off with uvc_function_set_alt > usb: gadget: uvc: remove delay usb status phase from uvc > usb: gadget: uvc: disable stream when disconnected > > drivers/usb/gadget/function/f_uvc.c | 14 +++++++++++--- > drivers/usb/gadget/function/uvc.h | 2 ++ > drivers/usb/gadget/function/uvc_v4l2.c | 21 +++++++++++++++------ > 3 files changed, 28 insertions(+), 9 deletions(-) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
