linux-kernel - Re: [PATCH 2/2] PCI: rcar: Resolve of_find_matching

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Message-ID: <CAMuHMdUwGLDzOQo_wwSLmzBnJXe-cOw=nqsPbFLsj-c+nHfy_w@mail.gmail.com>
Date:   Wed, 22 Jun 2022 09:45:49 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Marek Vasut <marek.vasut+renesas@...il.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Liang He <windhl@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 2/2] PCI: rcar: Resolve of_find_matching_node() reference leak

Hi Bjorn,

On Wed, Jun 22, 2022 at 4:57 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
>
> Previously, rcar_pcie_init() used of_find_matching_node() to search the
> entire device tree for compatible strings for which we need to install an
> abort handler.  If we found one, we got a device_node with refcount
> incremented, but we discarded the pointer and never released that
> reference.
>
> Extend the struct rcar_variant to indicate whether each variant requires an
> abort handler.  Install the handler in rcar_pcie_probe() when needed.
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Liang He <windhl@....com>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>

Thanks for your patch!

> --- a/drivers/pci/controller/pcie-rcar-host.c
> +++ b/drivers/pci/controller/pcie-rcar-host.c

> @@ -964,12 +965,35 @@ static int rcar_pcie_parse_map_dma_ranges(struct rcar_pcie_host *host)
>         return err;
>  }
>
> +#ifdef CONFIG_ARM
> +static int rcar_pcie_aarch32_abort_handler(unsigned long addr,
> +               unsigned int fsr, struct pt_regs *regs)
> +{
> +       return !fixup_exception(regs);
> +}
> +#endif
> +
> +static void rcar_pcie_hook_aborts(void)
> +{
> +#ifdef CONFIG_ARM
> +#ifdef CONFIG_ARM_LPAE
> +       hook_fault_code(17, rcar_pcie_aarch32_abort_handler, SIGBUS, 0,
> +                       "asynchronous external abort");
> +#else
> +       hook_fault_code(22, rcar_pcie_aarch32_abort_handler, SIGBUS, 0,
> +                       "imprecise external abort");
> +#endif
> +#endif
> +}
> +
>  static const struct rcar_variant rcar_h1_data = {
>         .phy_init_fn = rcar_pcie_phy_init_h1,
> +       .hook_aborts = true,
>  };
>
>  static const struct rcar_variant rcar_gen2_data = {
>         .phy_init_fn = rcar_pcie_phy_init_gen2,
> +       .hook_aborts = true,
>  };
>
>  static const struct rcar_variant rcar_gen3_data = {
> @@ -1035,6 +1059,9 @@ static int rcar_pcie_probe(struct platform_device *pdev)
>                 goto err_clk_disable;
>         }
>
> +       if (host->variant->hook_aborts)
> +               rcar_pcie_hook_aborts();

I was quite sure there was a good reason why this was not done in
.probe() before...

And indeed, the original submission[1] did have a comment explaining
that:

    + /*
    + * Since probe() can be deferred we need to make sure that
    + * hook_fault_code is not called after __init memory is freed
    + * by kernel and since rcar_pcie_abort_handler() is a no-op,
    + * we can install the handler here without risking it
    + * accessing some uninitialized driver state.
    + */

No idea why it was removed in v2 and later, but the point is:
hook_fault_code() is __init, so you cannot call it from a deferred
probe.
And you should have got a section mismatch warning ;-)

[1] https://lore.kernel.org/all/20200912211853.15321-1-marek.vasut@gmail.com/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds