Re: [PATCH v1 0/3] usb: gadget: uvc: stability fixes on STREAMOFF.

[Michael Grzeschik <mgr@pengutronix.de>]

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Hi Laurent

On Thu, Oct 05, 2023 at 11:23:27AM +0300, Laurent Pinchart wrote:
>On Tue, Oct 03, 2023 at 01:09:06PM +0200, Michael Grzeschik wrote:
>> On Sat, Sep 30, 2023 at 11:48:18AM -0700, Avichal Rakesh wrote:
>> > We have been seeing two main stability issues that uvc gadget driver
>> > runs into when stopping streams:
>> >  1. Attempting to queue usb_requests to a disabled usb_ep
>> >  2. use-after-free issue for inflight usb_requests
>> >
>> > The three patches below fix the two issues above. Patch 1/3 fixes the
>> > first issue, and Patch 2/3 and 3/3 fix the second issue.
>> >
>> > Avichal Rakesh (3):
>> >   usb: gadget: uvc: prevent use of disabled endpoint
>> >   usb: gadget: uvc: Allocate uvc_requests one at a time
>> >   usb: gadget: uvc: Fix use-after-free for inflight usb_requests
>> >
>> > drivers/usb/gadget/function/f_uvc.c     |  11 +-
>> > drivers/usb/gadget/function/f_uvc.h     |   2 +-
>> > drivers/usb/gadget/function/uvc.h       |   6 +-
>> > drivers/usb/gadget/function/uvc_v4l2.c  |  21 ++-
>> > drivers/usb/gadget/function/uvc_video.c | 189 +++++++++++++++++-------
>> > 5 files changed, 164 insertions(+), 65 deletions(-)
>>
>> These patches are not applying on gregkh/usb-testing since
>> Greg did take my patches first. I have already rebased them.
>
>I think they got merged too soon :-( We could fix things on top, but
>there's very little time to do so for v6.7.

Agreed. I was jumping from one workaround to another one, since this
is not easy to fix in a proper way. And still after this long discussion
with Avichal I don't think we are there yet.


So far the first two patches from Avichal look legit. But the overall
Use-After-Free fix is yet to be done properly.

The "abondoned" method he suggested is really bad to follow and will
add too much complexity and will be hard to debug.

IMHO it should be possible to introduce two cleanup pathes.

One path would be in the uvc_cleanup_requests that will cleanup the
requests that are actually not used in the controller and are registered
in the req_free list.

The second path would be the complete functions that are being run
from the controller and will ensure that the cleanup will really free
the requests from the controller after they were consumed.

What do you think?

Regards,
Michael

>> In the updated version I the stack runs into the
>> following error, when enabling lockdep. Could you
>> try your version with lockdep enabled?
>>
>> [   41.278520] configfs-gadget.vz gadget.0: uvc: reset UVC
>> [   47.156261] configfs-gadget.vz gadget.0: uvc: uvc_function_set_alt(2, 0)
>> [   47.169177]
>> [   47.170903] ============================================
>> [   47.176857] WARNING: possible recursive locking detected
>> [   47.182798] 6.5.0-20230919-1+ #19 Tainted: G         C
>> [   47.189323] --------------------------------------------
>> [   47.195256] vzuvcd/412 is trying to acquire lock:
>> [   47.200511] ffffff8009560928 (&video->req_lock){....}-{3:3}, at: uvc_video_complete+0x44/0x2e0
>> [   47.210172]
>> [   47.210172] but task is already holding lock:
>> [   47.216687] ffffff8009560928 (&video->req_lock){....}-{3:3}, at: uvcg_video_enable+0x2d0/0x5c0
>> [   47.226333]
>> [   47.226333] other info that might help us debug this:
>> [   47.233625]  Possible unsafe locking scenario:
>> [   47.233625]
>> [   47.240242]        CPU0
>> [   47.242974]        ----
>> [   47.245709]   lock(&video->req_lock);
>> [   47.249802]   lock(&video->req_lock);
>> [   47.253897]
>> [   47.253897]  *** DEADLOCK ***
>> [   47.253897]
>> [   47.260511]  May be due to missing lock nesting notation
>> [   47.260511]
>
>-- 
>Regards,
>
>Laurent Pinchart
>

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