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Date: Thu, 2 May 2024 18:31:48 +0300
From: Andy Shevchenko <andriy.shevchenko@intel.com>
To: Hardik Gajjar <hgajjar@de.adit-jv.com>
Cc: Ferry Toth <fntoth@gmail.com>, gregkh@linuxfoundation.org,
	s.hauer@pengutronix.de, jonathanh@nvidia.com,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	quic_linyyuan@quicinc.com, paul@crapouillou.net,
	quic_eserrao@quicinc.com, erosca@de.adit-jv.com
Subject: Re: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with
 netif_device_detach
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On Thu, May 02, 2024 at 05:29:16PM +0200, Hardik Gajjar wrote:
> 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.

Since we are almost at -rc7, I propose to revert and try again next cycle.

> 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