usb: gadget: Kernel panic (NULL pointer dereference) when using fsl_udc2_core on i.MX31 PDK

[Felipe Balbi]

Hi,

Magnus Lilja <lilja.magnus at gmail.com> writes:
> Hi
>
> I tried the fsl_udc_core gadget driver on the i.MX31 PDK board and got a 
> kernel panic (NULL pointer dereference) when connecting the USB cable. I 
> had the g_serial module loaded as well.
>
> The NULL pointer panic comes from gadget/udc/core.c 
> usb_gadget_giveback_request() which calls req->complete() and in some 
> cases req->complete is NULL.
>
> Commit 304f7e5e1d08 ("usb: gadget: Refactor request completion") changed 
> fsl_udc2_core.c (and several other files) and in fsl_udc2_core.c a check 
> that req->complete is non-NULL was removed:
>
> --- a/drivers/usb/gadget/udc/fsl_udc_core.c
> +++ b/drivers/usb/gadget/udc/fsl_udc_core.c
> @@ -197,10 +197,8 @@ __acquires(ep->udc->lock)
>          ep->stopped = 1;
>
>          spin_unlock(&ep->udc->lock);
> -       /* complete() is from gadget layer,
> -        * eg fsg->bulk_in_complete() */
> -       if (req->req.complete)
> -               req->req.complete(&ep->ep, &req->req);
> +
> +       usb_gadget_giveback_request(&ep->ep, &req->req);
>
>          spin_lock(&ep->udc->lock);
>          ep->stopped = stopped;
>
> If I re-introduce the check (either in fsl_udc_core.c or core.c) at 
> least USB gadget operation using g_serial seems to work just fine.
>
> I don't know the logic in detail to understand whether this is a proper 
> fix or if there is some other more problem with the fls_udc_core driver. 
> Does anyone have input in this matter?
>
> I can produce a proper patch that fixes this problem by re-introducing 
> the check (in either fsl_udc_core.c or core.c) if that is a proper 
> solution and I can also assist in testing other fixes to the problem.

->complete() is supposed to be mandatory. Which gadget do you have that
->doesn't set ->complete() to a valid function pointer?

-- 
balbi
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