Re: [PATCH v2 1/3] Revert "usb: gadget: u_audio: add real feedback implementation"

[Ferry Toth]

Op 27-08-2021 om 10:29 schreef Greg Kroah-Hartman:
> On Thu, Aug 26, 2021 at 08:57:37PM +0200, Ferry Toth wrote:
> > This reverts commit e89bb4288378b85c82212b60dc98ecda6b3d3a70.
> >
> > The commit is part of a series with commit
> > 24f779dac8f3efb9629adc0e486914d93dc45517 causing a BUG on dwc3
> > hardware, at least on Intel Merrifield platform when configured
> > through configfs:
> > BUG: kernel NULL pointer dereference, address: 0000000000000008
> > ...
> > RIP: 0010:dwc3_gadget_del_and_unmap_request+0x19/0xe0
> > ...
> > Call Trace:
> >   dwc3_remove_requests.constprop.0+0x12f/0x170
> >   __dwc3_gadget_ep_disable+0x7a/0x160
> >   dwc3_gadget_ep_disable+0x3d/0xd0
> >   usb_ep_disable+0x1c/0x70
> >   u_audio_stop_capture+0x79/0x120 [u_audio]
> >   afunc_set_alt+0x73/0x80 [usb_f_uac2]
> >   composite_setup+0x224/0x1b90 [libcomposite]
> >
> > Pavel's suggestion to add
> > `echo "adaptive" > functions/uac2.usb0/c_sync` to the configfs script
> > resolves the issue.
> > Thinh suggests "the crash is probably because of f_uac2 prematurely
> > freeing feedback request before its completion. usb_ep_dequeue() is
> > asynchronous. dwc2() may treat it as a synchronous call so you didn't
> > get a crash."
> >
> > Revert as this is a regression and the kernel shouldn't crash depending
> > on configuration parameters.
>
> Are these normal configuration options in the wild, or is this just
> something that you "can do"?

It's a work around suggested by Pavel, a line that can be added to 
configfs script.

> > Signed-off-by: Ferry Toth <ftoth@xxxxxxxxxxxxxx>
>
> I need an ack from the original authors to revert all this...

A fix has appeared:
https://lore.kernel.org/linux-usb/1jfsuvw817.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#m922149b7e74204c8ed1bed2c624910ab4eafd43c

This has been acked by Felipe. If we can get that in 5.14.0 it would be 
preferable to reverting this series.

> thanks,
>
> greg k-h