Date: Thu, 2 May 2024 22:13:43 +0200
From: Ferry Toth <fntoth@...il.com>
To: Hardik Gajjar <hgajjar@...adit-jv.com>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>,
 gregkh@...uxfoundation.org, s.hauer@...gutronix.de, jonathanh@...dia.com,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
 quic_linyyuan@...cinc.com, paul@...pouillou.net, quic_eserrao@...cinc.com,
 erosca@...adit-jv.com
Subject: Re: [PATCH v4] usb: gadget: u_ether: Replace netif_stop_queue with
 netif_device_detach

Op 02-05-2024 om 17:29 schreef Hardik Gajjar:
> On Tue, Apr 30, 2024 at 11:12:17PM +0200, Ferry Toth wrote:
>> Hi,
>>
>> Op 30-04-2024 om 21:40 schreef Ferry Toth:
>>> Hi,
>>>
>>> Op 30-04-2024 om 17:32 schreef Hardik Gajjar:
>>>> On Sun, Apr 28, 2024 at 11:07:36PM +0200, Ferry Toth wrote:
>>>>> Hi,
>>>>>
>>>>> Op 25-04-2024 om 23:27 schreef Ferry Toth:
>>>>>> Hi,
>>>>>>
>>>>>> 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@...a:~# 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@...a:~# 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@...a:~# 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@...a:~# 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@...a:~# 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@...a:~# 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@...a:~# 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@...a:/sys/kernel/tracing# echo 'gether_*' > set_ftrace_filter
>>>>> root@...a:/sys/kernel/tracing# echo 'eem_*' >> set_ftrace_filter
>>>>> root@...a:/sys/kernel/tracing# echo function > current_tracer
>>>>> root@...a:/sys/kernel/tracing# echo 'reset_config' >> set_ftrace_filter
>>>>> -> switch to host mode then back to device
>>>>> root@...a:/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, < 300 lines remain. See attached tar.gz for you to compare.

> 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.
>>>
>>>> Hardik
>>>>
>>>>
>>>>>
>>>>>>
>>>>>>> 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
>>>>>>>>
>>>>>>>>
>>>>>>
>>>

Download attachment "trace-u_ether.tar.gz" of type "application/gzip" (1484 bytes)

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