Am Dienstag, den 06.08.2019, 10:19 -0400 schrieb Alan Stern:
> On Tue, 6 Aug 2019, Oliver Neukum wrote:
>
> > Am Donnerstag, den 01.08.2019, 14:47 -0400 schrieb Alan Stern:
> > >
> > > I think this must be caused by an unbalanced refcount. That is,
> > > something must drop one more reference to the device than it takes.
> > > That would explain why the invalid access occurs inside a single
> > > bus_remove_device() call, between the klist_del() and
> > > device_release_driver().
> > >
> > > The kernel log indicates that the device was probed by rndis_wlan,
> > > rndis_host, and cdc_acm, all of which got errors because of the
> > > device's bogus descriptors. Probably one of them is messing up the
> > > refcount.
> >
> > Hi,
> >
> > you made me look at cdc-acm. I suspect
> >
> > cae2bc768d176bfbdad7035bbcc3cdc973eb7984 ("usb: cdc-acm: Decrement tty port's refcount if probe() fail")
> >
> > is buggy decrementing the refcount on the interface in destroy()
> > even before the refcount is increased.
> >
> > Unfortunately I cannot tell from the bug report how many and which
> > interfaces the emulated test device has. Hence it is unclear to me,
> > when exactly probe() would fail cdc-acm.
>
> Only one interface (numbered 234!).
Yes. cdc-acm went into the look_for_collapsed_interface code path.
But I cannot tell whether it proceeded to made_compressed_probe
(Yes, I know the code makes extensive use of "goto")
> > If you agree. I am attaching a putative fix.
>
> Your patch adds a line saying:
>
> > + usb_get_intf(acm->control); /* undone in destroy() */
>
> but I don't see any destroy() function in that source file. Did you
> mean acm_port_destruct()?
Yes, sorry
> In any case, I don't know if this missing "get" would cause the
> problem, but it might well.
Then let's wait for the result.
Regards
Oliver
