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Date:   Thu, 17 Mar 2022 12:07:51 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>, linux-usb@vger.kernel.org,
        kernel@pengutronix.de
Subject: Re: refcount underflow on stm32mp1
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On Thu, Mar 17, 2022 at 11:49:49AM +0100, Uwe Kleine-König wrote:
> On Wed, Mar 16, 2022 at 10:44:37PM +0100, Uwe Kleine-König wrote:
> > The problem is that after usb_add_gadget_udc() failed in
> > dwc2_driver_probe(), dwc2_hsotg_remove() -> usb_del_gadget_udc() ->
> > usb_put_gadget() -> put_device() results in that underflow.
> > 
> > With that information I'd expect that someone understanding how
> > reference counting works with usb gadgets should be able to come up with
> > a fix.
> 
> The problem is that usb_add_gadget_udc() failing already calls
> usb_put_gadget() and so dwc2_hsotg_remove() must not call it again when
> called from dwc2_driver_probe.
> 
> I don't understand that udc stuff enough to be confident that a patch I
> create for that will do the right thing.

You should CC: the maintainer of the dwc2 driver.  That's the best 
person to know how to fix dwc2_hsotg_remove().

Alan Stern