If you encounter uvc_disconnect then you may have a different issue
than I do. I can clearly see via debugging that uvc_disconnect is
never reached. In my case the disconnect is happening in
usb/core/hub.c:usb_disconnect. The comment on top if this function
says "This call is synchronous, and
Sorry I kept the thin USB extension cable that I used to reproduce this. I
will try the patch in #23 over the next week or so when I can find time. I
still don't think it will have any effect though as the issue seems to be
in usbcore. Happy to see once and for all.
John
On Tue, Jan 18, 2022
Sorry this only seems reproducible in a scenario a USB switch or cable that
doesn't support enough amps for the device. Any device or webcam which
overloads its power supply and then disconnects during UVC initialization
will disconnect itself during a critical period in the kernel where an
Sorry I've been reluctant to test it since that code block is never even
hit during the issue.
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https://bugs.launchpad.net/bugs/1827452
Title:
null pointer dereference in uvcvideo
To
@kaihengfeng
The usb disconnect comes directly via interrupt. Execution doesn't hit
uvc_disconnect and this patch has no effect. :/
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Title:
Thanks I finally managed to set up the same test cable and give this
patch a go. I still see the same error - third attempt in the trace
attached. I'm still of the opinion that this would need to be fixed in
usbcore.
** Attachment added: "dmesg failure on 3rd attempt"
Thanks I will test as soon as I get some time (weekend). I have to hook
up my shoddy tester USB cable and compile a fresh kernel but in the
meantime trying to get business wrapped up before holidays.
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There it is: https://lore.kernel.org/linux-
media/CAO5W59geLtP7kHJkW=ELusAcd9==ceqhsuzznukfradtkxz...@mail.gmail.com/
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Title:
null pointer
Yes this was the original thread. Alan was helpful and responsive but
in the end he suggested I contact the uvcvideo maintainers which I did
and got nowhere.
https://lore.kernel.org/linux-
usb/20201123152654.gb708...@rowland.harvard.edu/#t
The 2nd patch was to uvcvideo maintainers Laurent
I shared the stack trace. Was there a reply somewhere I didn't get? Is
it on lkms? Link?
With UVC trace on:
[ 638.729455] uvcvideo: uvc_v4l2_open
[ 638.824646] uvcvideo: Resuming interface 0
[ 638.824648] uvcvideo: Resuming interface 1
[ 638.825644] uvcvideo: uvc_v4l2_release
[
Hi latest on this. I've played with about 50 custom kernel patches here
and I can see exactly what happens. When uvcvideo looks for webcam
devices it finds a perfectly healthy idle webcam on the USB hub (even
built-in hub). Then when it starts a stream the webcam obviously
requires more power.
Update again.
The kernel maintainers have been helpful but prefer NULL checking to be done in
the drivers, not in the kernel. I've explored further with some test builds
and it turns out the NULL is actually on the dev config interfaces (usb.c:281
current line). During initialization the
Update on this. Pretty sure I managed to find the line in the kernel
triggering this. I've submitted a PR to the kernel USB maintainers.
Hopefully tested and merged soon.
https://github.com/torvalds/linux/commit/a40519014549f60969c8e67a2fd91426db05fe04
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I know this is closed but I've been having this same issue for months as
well. In fact I tried a different webcam from a different vendor and I
see the same behaviour.
Linux 5.8.18-200.fc32.x86_64 #1 SMP Mon Nov 2 19:49:11 UTC 2020 x86_64
x86_64 x86_64 GNU/Linux
Just adding this for the record,
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