Re: [RFC PATCH v2 0/6] net: wwan: add NMEA port type support

[Daniele Palmas <dnlplm@gmail.com>]

Hi Sergey and Loic,

Il giorno mer 8 ott 2025 alle ore 23:00 Sergey Ryazanov
<ryazanov.s.a@gmail.com> ha scritto:
>
> Hi Loic, Daniele,
>
> On 10/2/25 18:44, Loic Poulain wrote:
> > On Tue, Sep 30, 2025 at 9:22 AM Daniele Palmas <dnlplm@gmail.com> wrote:
> > [...]
> >> diff --git a/drivers/net/wwan/wwan_hwsim.c b/drivers/net/wwan/wwan_hwsim.c
> >> index a748b3ea1602..e4b1bbff9af2 100644
> >> --- a/drivers/net/wwan/wwan_hwsim.c
> >> +++ b/drivers/net/wwan/wwan_hwsim.c
> >> @@ -236,7 +236,7 @@ static void wwan_hwsim_nmea_emul_timer(struct timer_list *t)
> >>          /* 43.74754722298909 N 11.25759835922875 E in DMM format */
> >>          static const unsigned int coord[4 * 2] = { 43, 44, 8528, 0,
> >>                                                     11, 15, 4559, 0 };
> >> -       struct wwan_hwsim_port *port = from_timer(port, t, nmea_emul.timer);
> >> +       struct wwan_hwsim_port *port = timer_container_of(port, t,
> >> nmea_emul.timer);
> >>
> >> it's basically working fine in operative mode though there's an issue
> >> at the host shutdown, not able to properly terminate.
> >>
> >> Unfortunately I was not able to gather useful text logs besides the picture at
> >>
> >> https://drive.google.com/file/d/13ObWikuiMMUENl2aZerzxFBg57OB1KNj/view?usp=sharing
> >>
> >> showing an oops with the following call stack:
> >>
> >> __simple_recursive_removal
> >> preempt_count_add
> >> __pfx_remove_one
> >> wwan_remove_port
> >> mhi_wwan_ctrl_remove
> >> mhi_driver_remove
> >> device_remove
> >> device_del
> >>
> >> but the issue is systematic. Any idea?
> >>
> >> At the moment I don't have the time to debug this deeper, I don't even
> >> exclude the chance that it could be somehow related to the modem. I
> >> would like to further look at this, but I'm not sure exactly when I
> >> can....
> >
> > Thanks a lot for testing, Sergey, do you know what is wrong with port removal?
>
> Daniele, thanks a lot for verifying the proposal on a real hardware and
> sharing the build fix.
>
> Unfortunately, I unable to reproduce the crash. I have tried multiple
> times to reboot a VM running the simulator module even with opened GNSS
> device. No luck. It reboots and shutdowns smoothly.
>

I've probably figured out what's happening.

The problem seems that the gnss device is not considered a wwan_child
by is_wwan_child and this makes device_unregister in wwan_remove_dev
to be called twice.

For testing I've overwritten the gnss device class with the following hack:

diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
index 4d29fb8c16b8..32b3f7c4a402 100644
--- a/drivers/net/wwan/wwan_core.c
+++ b/drivers/net/wwan/wwan_core.c
@@ -599,6 +599,7 @@ static int wwan_port_register_gnss(struct wwan_port *port)
                gnss_put_device(gdev);
                return err;
        }
+       gdev->dev.class = &wwan_class;

        dev_info(&wwandev->dev, "port %s attached\n", dev_name(&gdev->dev));

and now the system powers off without issues.

So, not sure how to fix it properly, but at least does the analysis
make sense to you?

Thanks,
Daniele

> --
> Sergey