Re: [RFC PATCH net-next 1/5] net: dsa: realtek-smi: fix mdio_free bug on module unload

[Vladimir Oltean <olteanv@gmail.com>]

On Sun, Aug 22, 2021 at 09:31:39PM +0200, Alvin Šipraga wrote:
> From: Alvin Šipraga <alsi@bang-olufsen.dk>
> 
> realtek-smi-core fails to unregister the slave MII bus on module unload,
> raising the following BUG warning:
> 
>     mdio_bus.c:650: BUG_ON(bus->state != MDIOBUS_UNREGISTERED);
> 
>     kernel BUG at drivers/net/phy/mdio_bus.c:650!
>     Internal error: Oops - BUG: 0 [#1] PREEMPT_RT SMP
>     Call trace:
>      mdiobus_free+0x4c/0x50
>      devm_mdiobus_free+0x18/0x20
>      release_nodes.isra.0+0x1c0/0x2b0
>      devres_release_all+0x38/0x58
>      device_release_driver_internal+0x124/0x1e8
>      driver_detach+0x54/0xe0
>      bus_remove_driver+0x60/0xd8
>      driver_unregister+0x34/0x60
>      platform_driver_unregister+0x18/0x20
>      realtek_smi_driver_exit+0x14/0x1c [realtek_smi]
> 
> Fix this by duly unregistering the slave MII bus with
> mdiobus_unregister. We do this in the DSA teardown path, since
> registration is performed in the DSA setup path.
> 
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Fixes: d8652956cf37 ("net: dsa: realtek-smi: Add Realtek SMI driver")
> Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
> ---
>  drivers/net/dsa/realtek-smi-core.c | 6 ++++++
>  drivers/net/dsa/realtek-smi-core.h | 1 +
>  drivers/net/dsa/rtl8366rb.c        | 8 ++++++++
>  3 files changed, 15 insertions(+)
> 
> diff --git a/drivers/net/dsa/realtek-smi-core.c b/drivers/net/dsa/realtek-smi-core.c
> index 8e49d4f85d48..6992b6b31db6 100644
> --- a/drivers/net/dsa/realtek-smi-core.c
> +++ b/drivers/net/dsa/realtek-smi-core.c
> @@ -383,6 +383,12 @@ int realtek_smi_setup_mdio(struct realtek_smi *smi)
>  	return ret;
>  }
>  
> +void realtek_smi_teardown_mdio(struct realtek_smi *smi)
> +{
> +	if (smi->slave_mii_bus)
> +		mdiobus_unregister(smi->slave_mii_bus);
> +}
> +
>  static int realtek_smi_probe(struct platform_device *pdev)
>  {
>  	const struct realtek_smi_variant *var;
> diff --git a/drivers/net/dsa/realtek-smi-core.h b/drivers/net/dsa/realtek-smi-core.h
> index fcf465f7f922..6cfa5f2df7ea 100644
> --- a/drivers/net/dsa/realtek-smi-core.h
> +++ b/drivers/net/dsa/realtek-smi-core.h
> @@ -119,6 +119,7 @@ struct realtek_smi_variant {
>  int realtek_smi_write_reg_noack(struct realtek_smi *smi, u32 addr,
>  				u32 data);
>  int realtek_smi_setup_mdio(struct realtek_smi *smi);
> +void realtek_smi_teardown_mdio(struct realtek_smi *smi);
>  
>  /* RTL8366 library helpers */
>  int rtl8366_mc_is_used(struct realtek_smi *smi, int mc_index, int *used);
> diff --git a/drivers/net/dsa/rtl8366rb.c b/drivers/net/dsa/rtl8366rb.c
> index a89093bc6c6a..6537fac7aba4 100644
> --- a/drivers/net/dsa/rtl8366rb.c
> +++ b/drivers/net/dsa/rtl8366rb.c
> @@ -982,6 +982,13 @@ static int rtl8366rb_setup(struct dsa_switch *ds)
>  	return 0;
>  }
>  
> +static void rtl8366rb_teardown(struct dsa_switch *ds)
> +{
> +	struct realtek_smi *smi = ds->priv;
> +
> +	realtek_smi_teardown_mdio(smi);
> +}
> +

Objection: dsa_switch_teardown has:

	if (ds->slave_mii_bus && ds->ops->phy_read)
		mdiobus_unregister(ds->slave_mii_bus);

The realtek_smi_setup_mdio function does:

	smi->ds->slave_mii_bus = smi->slave_mii_bus;

so I would expect that this would result in a double unregister on some
systems.

I haven't went through your new driver, but I wonder whether you have
the phy_read and phy_write methods implemented? Maybe that is the
difference?

>  static enum dsa_tag_protocol rtl8366_get_tag_protocol(struct dsa_switch *ds,
>  						      int port,
>  						      enum dsa_tag_protocol mp)
> @@ -1505,6 +1512,7 @@ static int rtl8366rb_detect(struct realtek_smi *smi)
>  static const struct dsa_switch_ops rtl8366rb_switch_ops = {
>  	.get_tag_protocol = rtl8366_get_tag_protocol,
>  	.setup = rtl8366rb_setup,
> +	.teardown = rtl8366rb_teardown,
>  	.phylink_mac_link_up = rtl8366rb_mac_link_up,
>  	.phylink_mac_link_down = rtl8366rb_mac_link_down,
>  	.get_strings = rtl8366_get_strings,
> -- 
> 2.32.0
>