Re: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with netif_device_detach

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Tue, May 28, 2024 at 09:18:51AM +0200, Hardik Gajjar wrote:
> On Sun, May 26, 2024 at 10:52:53PM +0200, Ferry Toth wrote:
> > Op 15-05-2024 om 20:38 schreef Ferry Toth:
> > > Op 10-05-2024 om 11:45 schreef Hardik Gajjar:
> > > > On Thu, May 02, 2024 at 10:32:16PM +0200, Ferry Toth wrote:
> > > > > Op 02-05-2024 om 22:13 schreef Ferry Toth:
> > > > > > Op 02-05-2024 om 17:29 schreef Hardik Gajjar:
> > > > > > > On Tue, Apr 30, 2024 at 11:12:17PM +0200, Ferry Toth wrote:
> > > > > > > > Op 30-04-2024 om 21:40 schreef Ferry Toth:
> > > > > > > > > Op 30-04-2024 om 17:32 schreef Hardik Gajjar:
> > > > > > > > > > On Sun, Apr 28, 2024 at 11:07:36PM +0200, Ferry Toth wrote:
> > > > > > > > > > > Op 25-04-2024 om 23:27 schreef Ferry Toth:
> > > > > > > > > > > > Op 17-04-2024 om 17:13 schreef Hardik Gajjar:
> > > > > > > > > > > > > On Tue, Apr 16, 2024 at 04:48:32PM +0300, Andy Shevchenko wrote:
> > > > > > > > > > > > > > On Thu, Apr 11, 2024 at 10:52:36PM +0200, Ferry Toth wrote:
> > > > > > > > > > > > > > > Op 11-04-2024 om 18:39 schreef Andy Shevchenko:
> > > > > > > > > > > > > > > > On Thu, Apr 11, 2024
> > > > > > > > > > > > > > > > at 04:26:37PM +0200,
> > > > > > > > > > > > > > > > Hardik Gajjar wrote:
> > > > > > > > > > > > > > > > > On Wed, Apr 10, 2024 at
> > > > > > > > > > > > > > > > > 08:37:42PM +0300, Andy
> > > > > > > > > > > > > > > > > Shevchenko wrote:
> > > > > > > > > > > > > > > > > > On Sun, Apr 07, 2024 at 10:51:51PM +0200, Ferry Toth wrote:
> > > > > > > > > > > > > > > > > > > Op 05-04-2024 om 13:38 schreef Hardik Gajjar:

> > > > > > > > > > > > > > ...

> > > > > > > > > > > > > > > > > > > Exactly. And this didn't happen before the 2 patches.
> > > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > > To be precise: /sys/class/net/usb0 is not
> > > > > > > > > > > > > > > > > > > removed and it is a link, the link
> > > > > > > > > > > > > > > > > > > target /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/net/usb0
> > > > > > > > > > > > > > > > > > > no
> > > > > > > > > > > > > > > > > > > longer exists
> > > > > > > > > > > > > > > > > So, it means that the /sys/class/net/usb0 is
> > > > > > > > > > > > > > > > > present, but the symlink is
> > > > > > > > > > > > > > > > > broken. In that case, the dwc3 driver should
> > > > > > > > > > > > > > > > > recreate the device, and the
> > > > > > > > > > > > > > > > > symlink should become active again
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > Yes, on first enabling gadget (when device mode is activated):
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > root@yuna:~# ls
> > > > > > > > > > > > > > > /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/
> > > > > > > > > > > > > > > driver  net  power  sound  subsystem  suspended  uevent
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > Then switching to host mode:
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > root@yuna:~# ls
> > > > > > > > > > > > > > > /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/
> > > > > > > > > > > > > > > ls: cannot access
> > > > > > > > > > > > > > > '/sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/':
> > > > > > > > > > > > > > > No such file
> > > > > > > > > > > > > > > or directory
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > Then back to device mode:
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > root@yuna:~# ls
> > > > > > > > > > > > > > > /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/
> > > > > > > > > > > > > > > driver  power  sound  subsystem  suspended  uevent
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > net is missing. But, network functions:
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > root@yuna:~# ping 10.42.0.1
> > > > > > > > > > > > > > > PING 10.42.0.1 (10.42.0.1): 56 data bytes
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > Mass storage device is
> > > > > > > > > > > > > > > created and removed each
> > > > > > > > > > > > > > > time as expected.
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > So, what's the conclusion?
> > > > > > > > > > > > > > Shall we move towards revert
> > > > > > > > > > > > > > of those
> > > > > > > > > > > > > > two changes?
> > > > > > > > > > > > > 
> > > > > > > > > > > > > 
> > > > > > > > > > > > > As promised, I have the tested
> > > > > > > > > > > > > the this patch with the dwc3
> > > > > > > > > > > > > gadget.
> > > > > > > > > > > > > I could not reproduce
> > > > > > > > > > > > > the issue.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > I can see the usb0 exist all the
> > > > > > > > > > > > > time and accessible regardless
> > > > > > > > > > > > > of
> > > > > > > > > > > > > the role switching of the USB mode (peripheral <-> host)
> > > > > > > > > > > > > 
> > > > > > > > > > > > > Following are the logs:
> > > > > > > > > > > > > //Host to device
> > > > > > > > > > > > > 
> > > > > > > > > > > > > console:/sys/bus/platform/devices/a800000.ssusb
> > > > > > > > > > > > > # echo "peripheral"
> > > > > > > > > > > > > > mode
> > > > > > > > > > > > > console:/sys/bus/platform/devices/a800000.ssusb # ls
> > > > > > > > > > > > > a800000.dwc3/gadget/net/
> > > > > > > > > > > > > usb0
> > > > > > > > > > > > > 
> > > > > > > > > > > > > //device to host
> > > > > > > > > > > > > console:/sys/bus/platform/devices/a800000.ssusb
> > > > > > > > > > > > > # echo "host" > mode
> > > > > > > > > > > > > console:/sys/bus/platform/devices/a800000.ssusb # ls
> > > > > > > > > > > > > a800000.dwc3/gadget/net/
> > > > > > > > > > > > > usb0
> > > > > > > > > > > > 
> > > > > > > > > > > > That is weird. When I switch to host mode (using
> > > > > > > > > > > > the physical switch),
> > > > > > > > > > > > the whole gadget directory is removed (now testing 6.9.0-rc5)
> > > > > > > > > > > > 
> > > > > > > > > > > > Switching back to device mode, that gadget
> > > > > > > > > > > > directory is recreated. And
> > > > > > > > > > > > gadget/sound as well, but not gadget/net.
> > > > > > > > > > > > 
> > > > > > > > > > > > > s a800000.dwc3/gadget/net/usb0
> > > > > > > > > > > > > <
> > > > > > > > > > > > > addr_assign_type    duplex             phys_port_name
> > > > > > > > > > > > > addr_len            flags              phys_switch_id
> > > > > > > > > > > > > address             gro_flush_timeout  power
> > > > > > > > > > > > > broadcast           ifalias            proto_down
> > > > > > > > > > > > > carrier             ifindex            queues
> > > > > > > > > > > > > carrier_changes     iflink             speed
> > > > > > > > > > > > > carrier_down_count  link_mode          statistics
> > > > > > > > > > > > > carrier_up_count    mtu                subsystem
> > > > > > > > > > > > > dev_id              name_assign_type   tx_queue_len
> > > > > > > > > > > > > dev_port            netdev_group       type
> > > > > > > > > > > > > device              operstate          uevent
> > > > > > > > > > > > > dormant             phys_port_id       waiting_for_supplier
> > > > > > > > > > > > > console:/sys/bus/platform/devices/a800000.ssusb
> > > > > > > > > > > > > # ifconfig -a usb0
> > > > > > > > > > > > > usb0      Link encap:Ethernet  HWaddr 3a:8b:63:97:1a:9a
> > > > > > > > > > > > >               BROADCAST MULTICAST  MTU:1500  Metric:1
> > > > > > > > > > > > >               RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> > > > > > > > > > > > >               TX packets:0
> > > > > > > > > > > > > errors:0 dropped:0 overruns:0
> > > > > > > > > > > > > carrier:0
> > > > > > > > > > > > >               collisions:0 txqueuelen:1000
> > > > > > > > > > > > >               RX bytes:0 TX bytes:0
> > > > > > > > > > > > > 
> > > > > > > > > > > > > console:/sys/bus/platform/devices/a800000.ssusb #
> > > > > > > > > > > > > 
> > > > > > > > > > > > > I strongly advise against
> > > > > > > > > > > > > reverting the patch solely based
> > > > > > > > > > > > > on the
> > > > > > > > > > > > > observed issue of removing the
> > > > > > > > > > > > > /sys/class/net/usb0 directory
> > > > > > > > > > > > > while
> > > > > > > > > > > > > the usb0 interface remains available.
> > > > > > > > > > > > 
> > > > > > > > > > > > There's more to it. I also mentioned that switching the role or
> > > > > > > > > > > > unplugging the cable leaves the usb0 connection.
> > > > > > > > > > > > 
> > > > > > > > > > > > I have while in host mode:
> > > > > > > > > > > > root@yuna:~# ifconfig -a usb0
> > > > > > > > > > > > usb0:
> > > > > > > > > > > > flags=-28605<UP,BROADCAST,RUNNING,MULTICAST,DYNAMIC>
> > > > > > > > > > > > mtu 1500
> > > > > > > > > > > >             inet 10.42.0.221  netmask 255.255.255.0  broadcast
> > > > > > > > > > > > 10.42.0.255
> > > > > > > > > > > >             inet6 fe80::a8bb:ccff:fedd:eef1  prefixlen 64
> > > > > > > > > > > > scopeid 0x20<link>
> > > > > > > > > > > > 
> > > > > > > > > > > > 
> > > > > > > > > > > > You don't see that because you didn't create a connection at all.
> > > > > > > > > > > > 
> > > > > > > > > > > > > Instead, I recommend enabling FTRACE to
> > > > > > > > > > > > > trace the functions involved
> > > > > > > > > > > > > and identify which faulty call is responsible for removing usb0.
> > > > > > > > > > > > 
> > > > > > > > > > > > Switching from device -> host -> device:
> > > > > > > > > > > > 
> > > > > > > > > > > > root@yuna:~# trace-cmd record -p function_graph -l *gether_*
> > > > > > > > > > > >       plugin 'function_graph'
> > > > > > > > > > > > Hit Ctrl^C to stop recording
> > > > > > > > > > > > ^CCPU0 data recorded at offset=0x1c8000
> > > > > > > > > > > >         188 bytes in size (4096 uncompressed)
> > > > > > > > > > > > CPU1 data recorded at offset=0x1c9000
> > > > > > > > > > > >         0 bytes in size (0 uncompressed)
> > > > > > > > > > > > root@yuna:~# trace-cmd report
> > > > > > > > > > > > cpus=2
> > > > > > > > > > > >          irq/68-dwc3-725   [000]   514.575337:
> > > > > > > > > > > > funcgraph_entry:      #
> > > > > > > > > > > > 2079.480 us |  gether_disconnect();
> > > > > > > > > > > >          irq/68-dwc3-946   [000]   524.263731:
> > > > > > > > > > > > funcgraph_entry:      +
> > > > > > > > > > > > 11.640 us  |  gether_disconnect();
> > > > > > > > > > > >          irq/68-dwc3-946   [000]   524.263743:
> > > > > > > > > > > > funcgraph_entry:      !
> > > > > > > > > > > > 116.520 us |  gether_connect();
> > > > > > > > > > > >          irq/68-dwc3-946   [000]   524.268029:
> > > > > > > > > > > > funcgraph_entry:      #
> > > > > > > > > > > > 2057.260 us |  gether_disconnect();
> > > > > > > > > > > >          irq/68-dwc3-946   [000]   524.270089:
> > > > > > > > > > > > funcgraph_entry:      !
> > > > > > > > > > > > 109.000 us |  gether_connect();
> > > > > > > > > > > 
> > > > > > > > > > > I tried to get a more useful trace:
> > > > > > > > > > > root@yuna:/sys/kernel/tracing# echo 'gether_*' > set_ftrace_filter
> > > > > > > > > > > root@yuna:/sys/kernel/tracing# echo 'eem_*' >> set_ftrace_filter
> > > > > > > > > > > root@yuna:/sys/kernel/tracing# echo function > current_tracer
> > > > > > > > > > > root@yuna:/sys/kernel/tracing# echo 'reset_config'
> > > > > > > > > > > > > set_ftrace_filter
> > > > > > > > > > > -> switch to host mode then back to device
> > > > > > > > > > > root@yuna:/sys/kernel/tracing# cat trace
> > > > > > > > > > > # tracer: function
> > > > > > > > > > > #
> > > > > > > > > > > # entries-in-buffer/entries-written: 53/53   #P:2
> > > > > > > > > > > #
> > > > > > > > > > > #                                _-----=> irqs-off/BH-disabled
> > > > > > > > > > > #                               / _----=> need-resched
> > > > > > > > > > > #                              | / _---=> hardirq/softirq
> > > > > > > > > > > #                              || / _--=> preempt-depth
> > > > > > > > > > > #                              ||| / _-=> migrate-disable
> > > > > > > > > > > #                              |||| /     delay
> > > > > > > > > > > #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
> > > > > > > > > > > #              | |         |   |||||     |         |
> > > > > > > > > > >         irq/68-dwc3-523     [000] D..3.   133.990254: reset_config
> > > > > > > > > > > <-__composite_disconnect
> > > > > > > > > > >         irq/68-dwc3-523     [000] D..3.   133.992274: eem_disable
> > > > > > > > > > > <-reset_config
> > > > > > > > > > >         irq/68-dwc3-523     [000] D..3.   133.992276:
> > > > > > > > > > > gether_disconnect
> > > > > > > > > > > <-reset_config
> > > > > > > > > > >         kworker/1:3-443     [001] ...1.   134.022453: eem_unbind
> > > > > > > > > > > <-purge_configs_funcs
> > > > > > > > > > > 
> > > > > > > > > > > -> to device mode
> > > > > > > > > > > 
> > > > > > > > > > >         kworker/1:3-443     [001] ...1.   148.630773: eem_bind
> > > > > > > > > > > <-usb_add_function
> > > > > > > > > > >         irq/68-dwc3-734     [000] D..3.   149.155209: eem_set_alt
> > > > > > > > > > > <-composite_setup
> > > > > > > > > > >         irq/68-dwc3-734     [000] D..3.   149.155215:
> > > > > > > > > > > gether_disconnect
> > > > > > > > > > > <-eem_set_alt
> > > > > > > > > > >         irq/68-dwc3-734     [000]
> > > > > > > > > > > D..3.   149.155220: gether_connect
> > > > > > > > > > > <-eem_set_alt
> > > > > > > > > > >         irq/68-dwc3-734     [000] D..3.   149.157287: eem_set_alt
> > > > > > > > > > > <-composite_setup
> > > > > > > > > > >         irq/68-dwc3-734     [000] D..3.   149.157292:
> > > > > > > > > > > gether_disconnect
> > > > > > > > > > > <-eem_set_alt
> > > > > > > > > > >         irq/68-dwc3-734     [000]
> > > > > > > > > > > D..3.   149.159338: gether_connect
> > > > > > > > > > > <-eem_set_alt
> > > > > > > > > > >         irq/68-dwc3-734     [000] D..2.   149.239625: eem_unwrap
> > > > > > > > > > > <-rx_complete
> > > > > > > > > > > ...
> > > > > > > > > > > 
> > > > > > > > > > > I don't know where to look exactly. Any hints?
> > > > > > > > > > 
> > > > > > > > > > do you see anything related to
> > > > > > > > > > gether_cleanup() after eem_unbind() ?
> > > > > > > > > 
> > > > > > > > > Nope. It's a pitty that the trace formatting got messed up
> > > > > > > > > above. But as
> > > > > > > > > you can see I traced gether_* and eem_*. After eem_unbind no traced
> > > > > > > > > function is called, until I flip the switch to device mode.
> > > > > > > > > The ... at the end is where I cut uninteresting eem_unwrap
> > > > > > > > > <-rx_complete
> > > > > > > > > and eem_wrap <-eth_start_xmit lines.
> > > > > > > > > 
> > > > > > > > > > If not then, you may try to enable tracing of TCP/IP stack and
> > > > > > > > > > network side to check who deleting the sysfs entry
> > > > > > > > > 
> > > > > > > > > Yes, that's a vast amount of functions to trace. And I don't see how
> > > > > > > > > that would be related to the patch we're
> > > > > > > > > discussing here. I was hoping
> > > > > > > > > for a little more targeted hint.
> > > > > > > > 
> > > > > > > > Now filtering 'gether_*', 'eem_*', '*configfs_*', 'composite_*',
> > > > > > > > 'usb_fun*',
> > > > > > > > 'reset_config' and 'device_remove_file' leads me to:
> > > > > > > > 
> > > > > > > > TIMESTAMP  FUNCTION
> > > > > > > >      |         |
> > > > > > > >     49.952477: eem_wrap <-eth_start_xmit
> > > > > > > >     55.072455: eem_wrap <-eth_start_xmit
> > > > > > > >     55.072621: eem_unwrap <-rx_complete
> > > > > > > >     59.011540: configfs_composite_reset <-usb_gadget_udc_reset
> > > > > > > >     59.011545: composite_reset <-configfs_composite_reset
> > > > > > > >     59.011548: reset_config <-__composite_disconnect
> > > > > > > >     59.013565: eem_disable <-reset_config
> > > > > > > >     59.013567: gether_disconnect <-reset_config
> > > > > > > >     59.049560: device_remove_file <-device_remove
> > > > > > > >     59.051185: configfs_composite_disconnect <-usb_gadget_disco
> > > > > > > >     59.051189: composite_disconnect <-configfs_composite_discon
> > > > > > > >     59.051195: configfs_composite_unbind <-gadget_unbind_driver
> > > > > > > >     59.052519: eem_unbind <-purge_configs_funcs
> > > > > > > >     59.052529: composite_dev_cleanup <-configfs_composite_unbin
> > > > > > > >     59.052537: device_remove_file <-composite_dev_cleanup
> > > > > > > > 
> > > > > > > > device_remove_file gets called twice, once by device_remove after
> > > > > > > > gether_disconnect (that the one). The 2nd time by
> > > > > > > > composite_dev_cleanup
> > > > > > > > (removing the gadget)
> > > > > > > 
> > > > > > > I believe that the device_remove_file function is only removing
> > > > > > > suspend-specific attributes, not the complete gadget.
> > > > > > > Typically, when you perform the role switch, the Gadget start/stop
> > > > > > > function in your UDC driver is called. These functions should not
> > > > > > > delete the gadget
> > > > > > > 
> > > > > > > To investigate further, could you please enable the DWC3 functions
> > > > > > > in ftrace and check who is removing the gadget?
> > > > > > > I can also enable this on my system and compare the logs with yours,
> > > > > > > but I will be in PI planning for 1.5 weeks and may not be able to
> > > > > > > provide immediate support.
> > > > > > 
> > > > > > Yes, but of course adding dwc3_* (and usb_*) also traces host mode, so
> > > > > > trace is 600kb. I cut uninteresting stuff before
> > > > > > configfs_composite_reset <-usb_gadget_udc_reset and after
> > > > > > __dwc3_set_mode, <https://urldefense.proofpoint.com/v2/url?u=http-3A__300linesremain.Seeattachedtar.gzforyouto&d=DwIDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=SAhjP5GOmrADp1v_EE5jWoSuMlYCIt9gKduw-DCBPLs&m=zdiBhk-2V5AXxu707QAhbCgWR4qNVRARBmxN17nVB69gVOm-QPqrJeKpo4_trszw&s=ixagWKgLs6wQDJfwh4vIDQNDiy8GZnK9KnUELIfiJz0&e=>
> > > > > > compare.
> > > > > > 
> > > > Could you please try with the following patch and see if your issue
> > > > resolves ?
> > > > 
> > > > diff --git a/drivers/usb/gadget/function/f_eem.c
> > > > b/drivers/usb/gadget/function/f_eem.c
> > > > index 3b445bd88498..c2a904475083 100644
> > > > --- a/drivers/usb/gadget/function/f_eem.c
> > > > +++ b/drivers/usb/gadget/function/f_eem.c
> > > > @@ -247,7 +247,7 @@ static int eem_bind(struct usb_configuration *c,
> > > > struct usb_function *f)
> > > >       struct usb_composite_dev *cdev = c->cdev;
> > > >       struct f_eem        *eem = func_to_eem(f);
> > > >       struct usb_string    *us;
> > > > -    int            status;
> > > > +    int            status = 0;
> > > >       struct usb_ep        *ep;
> > > >       struct f_eem_opts    *eem_opts;
> > > > @@ -260,16 +260,20 @@ static int eem_bind(struct usb_configuration
> > > > *c, struct usb_function *f)
> > > >        * with list_for_each_entry, so we assume no race condition
> > > >        * with regard to eem_opts->bound access
> > > >        */
> > > > +    mutex_lock(&eem_opts->lock);
> > > > +    gether_set_gadget(eem_opts->net, cdev->gadget);
> > > > +
> > > >       if (!eem_opts->bound) {
> > > > -        mutex_lock(&eem_opts->lock);
> > > > -        gether_set_gadget(eem_opts->net, cdev->gadget);
> > > >           status = gether_register_netdev(eem_opts->net);
> > > > -        mutex_unlock(&eem_opts->lock);
> > > > -        if (status)
> > > > -            return status;
> > > > -        eem_opts->bound = true;
> > > >       }
> > > > +    mutex_unlock(&eem_opts->lock);
> > > > +
> > > > +    if (status)
> > > > +        goto fail;
> > > > +
> > > > +    eem_opts->bound = true;
> > > > +
> > > >       us = usb_gstrings_attach(cdev, eem_strings,
> > > >                    ARRAY_SIZE(eem_string_defs));
> > > > 
> > > 
> > > After switching from host -> device -> host the usb0 device as seen by
> > > ifconfig remains "RUNNING" and in the routing table.
> > > 
> > > FYI This is the regression.
> > 
> > For us, I don't see any advantages in having this patch and only the
> > downside. Do you have any further ideas / patches that we could test.
> > 
> > Otherwise, it might be best to go with the original suggestion and revert
> > until it gets sorted out?
> 
> Hello,
> 
> Okay, lets revert the patch till we fix your problem. Would you be able to send the revert ? or shall I ?

Ferry or I can do it, but I will be able to do that next week.

> However, We are very much intrested to fix your problem and upstream the v2. 
> Therefore could you please share the following details to reproduce the issue
> - How did you created the gadget ? Could you please share the exact commands to create the eem gadget ?

Ferry will answer to this one.

> - Arch of your test bench (arm, x86)

x86, the SoC is Intel Tangier on the Intel Merrifield (platform).

> - How the DWC3 controller connected to your system ? via PCIe slot ? Could you please share the part number of the PCIe card ?

Yes, it's PCI connected device (which you may have already deducted from the
thread a lot of times). It's part of the SoC (also can be easily deducted).

The IDs are available in the driver:
https://elixir.bootlin.com/linux/latest/source/drivers/usb/dwc3/dwc3-pci.c#L24

> > > Also /sys/devices/pci0000:00/0000:00:11.0/dwc3.0.auto/gadget.0/net is
> > > still missing.
> > > 
> > > After deeper diving into v6.1.0, I found the latter a longer existing
> > > bug, not caused by your patch.
> > > 
> > > More over, this doesn't seem to do any harm.
> > > 
> > > The first issue does, as we try to route traffic over a device that no
> > > longer exists.
> > > 
> > > > > > > Additionally, please check if you have any customized DWC patches
> > > > > > > that may be causing this problem.
> > > > > > > 
> > > > > > > > > You may recall the whole issue did not occur before this
> > > > > > > > > patch got applied.

> > > > > > > > > > > > > According to current kernel architecture of u_ether driver, only
> > > > > > > > > > > > > gether_cleanup should remove the usb0 interface along with its
> > > > > > > > > > > > > kobject and sysfs interface.
> > > > > > > > > > > > > I suggest sharing the analysis
> > > > > > > > > > > > > here to understand why this
> > > > > > > > > > > > > practice
> > > > > > > > > > > > > is not followed in your use case or driver ?
> > > > > > > > > > > > 
> > > > > > > > > > > > Yes, I'll try to trace where that happens.
> > > > > > > > > > > > 
> > > > > > > > > > > > Nevertheless, the disappearance of the net/usb0 directory seems
> > > > > > > > > > > > harmless? But the usb: net device
> > > > > > > > > > > > remaining after disconnect or role
> > > > > > > > > > > > switch is not good, as the route remains.
> > > > > > > > > > > > 
> > > > > > > > > > > > May be they are 2 separate problems.
> > > > > > > > > > > > Could you try to reproduce what
> > > > > > > > > > > > happens if you make eem connection and then unplug?
> > > > > > > > > > > > 
> > > > > > > > > > > > > I am curious why the driver was
> > > > > > > > > > > > > developed without adhering to
> > > > > > > > > > > > > the
> > > > > > > > > > > > > kernel's gadget architecture.
> > > > > > > > > > > 
> > > > > > > > > > > I don't know what you mean here. Which driver do you mean?
> > > > > > > > > > > 
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > I have the dwc3 IP base usb controller, Let me check
> > > > > > > > > > > > > > > > > with this patch and
> > > > > > > > > > > > > > > > > share result here.  May be we need some fix in dwc3
> > > > > > > > > > > > > > > Would have been nice if someone could test on other
> > > > > > > > > > > > > > > controller as well. But
> > > > > > > > > > > > > > > another instance of dwc3 is also very welcome.
> > > > > > > > > > > > > > > > It's quite possible, please test on your side.
> > > > > > > > > > > > > > > > We are happy to test any fixes if you come up with.

-- 
With Best Regards,
Andy Shevchenko