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Date:   Wed, 4 Aug 2021 14:47:24 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, Andrew Lunn <andrew@...n.ch>
Cc:     Kevin Hilman <khilman@...libre.com>,
        Lee Jones <lee.jones@...aro.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/2] irqchip: irq-meson-gpio: make it possible to build as
 a module

On Wed, Aug 4, 2021 at 11:20 AM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Wed, Aug 4, 2021 at 1:50 AM Marc Zyngier <maz@...nel.org> wrote:
> >
> > On Wed, 04 Aug 2021 02:36:45 +0100,
> > Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > Hi Saravana,
> >
> > Thanks for looking into this.
>
> You are welcome. I just don't want people to think fw_devlink is broken :)
>
> >
> > [...]
> >
> > > > Saravana, could you please have a look from a fw_devlink perspective?
> > >
> > > Sigh... I spent several hours looking at this and wrote up an analysis
> > > and then realized I might be looking at the wrong DT files.
> > >
> > > Marc, can you point me to the board file in upstream that corresponds
> > > to the platform in which you see this issue? I'm not asking for [1],
> > > but the actual final .dts (not .dtsi) file that corresponds to the
> > > platform/board/system.
> >
> > The platform I can reproduce this on is described in
> > arch/arm64/boot/dts/amlogic/meson-sm1-khadas-vim3l.dts. It is an
> > intricate maze of inclusion, node merge and other DT subtleties. I
> > suggest you look at the decompiled version to get a view of the
> > result.
>
> Thanks. After decompiling it, it looks something like (stripped a
> bunch of reg and address properties and added the labels back):
>
> eth_phy: mdio-multiplexer@...00 {
>         compatible = "amlogic,g12a-mdio-mux";
>         clocks = <0x02 0x13 0x1e 0x02 0xb1>;
>         clock-names = "pclk\0clkin0\0clkin1";
>         mdio-parent-bus = <0x22>;
>
>         ext_mdio: mdio@0 {
>                 reg = <0x00>;
>
>                 ethernet-phy@0 {
>                         max-speed = <0x3e8>;
>                         interrupt-parent = <0x23>;
>                         interrupts = <0x1a 0x08>;
>                         phandle = <0x16>;
>                 };
>         };
>
>         int_mdio: mdio@1 {
>                 ...
>         }
> }
>
> And phandle 0x23 refers to the gpio_intc interrupt controller with the
> modular driver.
>
> > > Based on your error messages, it's failing for mdio@0 which
> > > corresponds to ext_mdio. But none of the board dts files in upstream
> > > have a compatible property for "ext_mdio". Which means fw_devlink
> > > _should_ propagate the gpio_intc IRQ dependency all the way up to
> > > eth_phy.
> > >
> > > Also, in the failing case, can you run:
> > > ls -ld supplier:*
> > >
> > > in the /sys/devices/....<something>/ folder that corresponds to the
> > > "eth_phy: mdio-multiplexer@...00" DT node and tell me what it shows?
> >
> > Here you go:
> >
> > root@...er-roach:~# find /sys/devices/ -name 'supplier*'|grep -i mdio | xargs ls -ld
> > lrwxrwxrwx 1 root root 0 Aug  4 09:47 /sys/devices/platform/soc/ff600000.bus/ff64c000.mdio-multiplexer/supplier:platform:ff63c000.system-controller:clock-controller -> ../../../../virtual/devlink/platform:ff63c000.system-controller:clock-controller--platform:ff64c000.mdio-multiplexer
>
> As we discussed over chat, this was taken after the mdio-multiplexer
> driver "successfully" probes this device. This will cause
> SYNC_STATE_ONLY device links created by fw_devlink to be deleted
> (because they are useless after a device probes). So, this doesn't
> show the info I was hoping to demonstrate.
>
> In any case, one can see that fw_devlink properly created the device
> link for the clocks dependency. So fw_devlink is parsing this node
> properly. But it doesn't create a similar probe order enforcing device
> link between the mdio-multiplexer and the gpio_intc because the
> dependency is only present in a grand child DT node (ethernet-phy@0
> under ext_mdio). So fw_devlink is working as intended.
>
> I spent several hours squinting at the code/DT yesterday. Here's what
> is going on and causing the problem:
>
> The failing driver in this case is
> drivers/net/mdio/mdio-mux-meson-g12a.c. And the only DT node it's
> handling is what I pasted above in this email. In the failure case,
> the call flow is something like this:
>
> g12a_mdio_mux_probe()
> -> mdio_mux_init()
> -> of_mdiobus_register(ext_mdio DT node)
> -> of_mdiobus_register_phy(ext_mdio DT node)
> -> several calls deep fwnode_mdiobus_phy_device_register(ethernet_phy DT node)
> -> Tried to get the IRQ listed in ethernet_phy and fails with
> -EPROBE_DEFER because the IRQ driver isn't loaded yet.
>
> The error is propagated correctly all the way up to of_mdiobus_register(), but
> mdio_mux_init() ignores the -EPROBE_DEFER from of_mdiobus_register() and just
> continues on with the rest of the stuff and returns success as long as
> one of the child nodes (in this case int_mdio) succeeds.
>
> Since the probe returns 0 without really succeeding, networking stuff
> just fails badly after this. So, IMO, the real problem is with
> mdio_mux_init() not propagating up the -EPROBE_DEFER. I gave Marc a
> quick hack (pasted at the end of this email) to test my theory and he
> confirmed that it fixes the issue (a few deferred probes later, things
> work properly).
>
> Andrew, I don't see any good reason for mdio_mux_init() not
> propagating the errors up correctly (at least for EPROBE_DEFER). I'll
> send a patch to fix this. Please let me know if there's a reason it
> has to stay as-is.

I sent out the proper fix as a series:
https://lore.kernel.org/lkml/20210804214333.927985-1-saravanak@google.com/T/#t

Marc, can you give it a shot please?

-Saravana

>
> -Saravana
>
> index 110e4ee85785..d973a267151f 100644
> --- a/drivers/net/mdio/mdio-mux.c
> +++ b/drivers/net/mdio/mdio-mux.c
> @@ -170,6 +170,9 @@ int mdio_mux_init(struct device *dev,
>                                 child_bus_node);
>                         mdiobus_free(cb->mii_bus);
>                         devm_kfree(dev, cb);
> +                       /* Not a final fix. I think it can cause UAF issues. */
> +                       mdio_mux_uninit(pb);
> +                       return r;
>                 } else {
>                         cb->next = pb->children;
>                         pb->children = cb;

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