linux-kernel - g_multi rmmod problem: usb_put_function_instance(fi

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Date:   Mon, 13 Jan 2020 16:16:15 +0100
From:   Martin Kepplinger <martin.kepplinger@...i.sm>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: g_multi rmmod problem: usb_put_function_instance(fi_acm) hangs

hi,

on the librem5 with defconfig
https://source.puri.sm/martin.kepplinger/linux-next/blob/next-20200110/librem5_cpuidle_mainline_atf/arch/arm64/configs/librem5_defconfig
running next-20200110 I load g_multi during startup.

rmmod g_multi results in error like
[  190.995685] dwc3 38100000.usb: timed out waiting for SETUP phase
or
[  109.702545] dwc3 38100000.usb: failed to enable ep0out

and hangs rmmod. What "fixes" the problem is the following change below.
Does that make any sense to you?

How would a real fix look like here, or how would I further debug?

thanks,
                                 martin

--- a/drivers/usb/gadget/legacy/multi.c
+++ b/drivers/usb/gadget/legacy/multi.c
@@ -459,7 +459,8 @@ static int multi_unbind(struct usb_composite_dev *cdev)
 #ifdef USB_ETH_RNDIS
        usb_put_function(f_acm_rndis);
 #endif
-       usb_put_function_instance(fi_acm);
+       /* FIXME the following hangs during rmmod */
+       // usb_put_function_instance(fi_acm);
 #ifdef USB_ETH_RNDIS
        usb_put_function(f_rndis);
        usb_put_function_instance(fi_rndis);