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

From: Ferry Toth
Date: Sun May 26 2024 - 16:53:08 EST


Hi

Op 15-05-2024 om 20:38 schreef Ferry Toth:
Hi,

Sorry to have kept you waiting, I was away for a short break.

Patch tested below.

Op 10-05-2024 om 11:45 schreef Hardik Gajjar:
On Thu, May 02, 2024 at 10:32:16PM +0200, Ferry Toth wrote:
Oops, sorry, wrong file attached . Now correct one.

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:
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@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?

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.

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