Hi Ulrich, What is the output of 'v4l2-ctl -D -d/dev/videoX' of the video device that causes the WARN_ON to appear? I can't tell what driver is used. The WARN_ON just checks if the capabilities field is a superset of the device_caps field. If not, then that's a driver bug. If this is an out-of-tree driver, then it has to be addressed there. Note that that WARN_ON has been there since mid-2019. Regards, Hans On 06/10/2024 12:50, Ulrich Drepper wrote: > I cannot really say when this problem started but I know that perhaps > six months back (or a bit more) I used the console successfully as a > video source device (webcam). This is a ATEM Mini Pro which has a > large number of USB interfaces. What trips up is videodev. Various > userlevel programs (uvcdynctrl, chromium) notice the device being > added and use ioctl(), triggering the problem. > > This is with the current Fedora x86_64 kernel (6.10.12) but a) it > happens for a while now and b) as far as I can see this is just the > upstream code, no local changes. > > The call trace is: > > Call Trace: > <TASK> > ? v4l_querycap+0x119/0x140 [videodev] > ? __warn.cold+0x8e/0xe8 > ? v4l_querycap+0x119/0x140 [videodev] > ? report_bug+0xff/0x140 > ? handle_bug+0x3c/0x80 > ? exc_invalid_op+0x17/0x70 > ? asm_exc_invalid_op+0x1a/0x20 > ? v4l_querycap+0x119/0x140 [videodev] > __video_do_ioctl+0x518/0x630 [videodev] > video_usercopy+0x1f1/0x7a0 [videodev] > > I traced the offending code to an 'ud2' instruction (makes sense, > undefined) which is reached from this code in > drivers/media/v4l2-core/v4l2-ioctl.c (v4l_querycap): > > WARN_ON((cap->capabilities & > (vfd->device_caps | V4L2_CAP_DEVICE_CAPS)) != > (vfd->device_caps | V4L2_CAP_DEVICE_CAPS)); > > The asm code is: > > 747e: 8b 73 54 mov 0x54(%rbx),%esi > 7481: 81 ca 00 00 00 80 or $0x80000000,%edx > 7487: 48 b9 00 00 20 00 00 movabs $0x20000000200000,%rcx > 748e: 00 20 00 > 7491: 48 0b 4b 54 or 0x54(%rbx),%rcx > 7495: 21 d6 and %edx,%esi > 7497: 39 f2 cmp %esi,%edx > 7499: 75 6e jne 7509 <v4l_querycap+0x119> > > where 7509 is the address of the ud2 instruction. > > The register dump shows > > RDX: 0000000085008003 RSI: 0000000085008002 > > which, if I'm right, means that cap->capabilities has the extra bit > > #define V4L2_CAP_VIDEO_CAPTURE 0x00000001 /* Is a video > capture device */ > > set. > > I don't know what 'ops' points to in the code. It seems to me that > the bit is set in the > > ops->vidioc_querycap(file, fh, cap); > > call just preceding the test. > > Just going by the name of the capability, it seems that the bit should > be set as this device is used as a camera as well so maybe the > information which comes from the call the > > struct video_device *vfd = video_devdata(file); > > is incomplete? Or the test WARN_ON condition is actually incorrect? > > > Any idea? I can try to run more tests if someone can tell me how to proceed. > > Thanks.
