linux-kernel - Re: [PATCH] staging: board: Fix uninitialized spinlock when attaching genpd

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Date:   Mon, 15 Feb 2021 10:37:11 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Magnus Damm <magnus.damm@...il.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: board: Fix uninitialized spinlock when attaching genpd

On Mon, Feb 15, 2021 at 7:14 AM Geert Uytterhoeven
<geert+renesas@...der.be> wrote:
>
> On Armadillo-800-EVA with CONFIG_DEBUG_SPINLOCK=y:
>
>     BUG: spinlock bad magic on CPU#0, swapper/1
>      lock: lcdc0_device+0x10c/0x308, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
>     CPU: 0 PID: 1 Comm: swapper Not tainted 5.11.0-rc5-armadillo-00036-gbbca04be7a80-dirty #287
>     Hardware name: Generic R8A7740 (Flattened Device Tree)
>     [<c010c3c8>] (unwind_backtrace) from [<c010a49c>] (show_stack+0x10/0x14)
>     [<c010a49c>] (show_stack) from [<c0159534>] (do_raw_spin_lock+0x20/0x94)
>     [<c0159534>] (do_raw_spin_lock) from [<c040858c>] (dev_pm_get_subsys_data+0x8c/0x11c)
>     [<c040858c>] (dev_pm_get_subsys_data) from [<c05fbcac>] (genpd_add_device+0x78/0x2b8)
>     [<c05fbcac>] (genpd_add_device) from [<c0412db4>] (of_genpd_add_device+0x34/0x4c)
>     [<c0412db4>] (of_genpd_add_device) from [<c0a1ea74>] (board_staging_register_device+0x11c/0x148)
>     [<c0a1ea74>] (board_staging_register_device) from [<c0a1eac4>] (board_staging_register_devices+0x24/0x28)
>
> of_genpd_add_device() is called before platform_device_register(), as it
> needs to attach the genpd before the device is probed.  But the spinlock
> is only initialized when the device is registered.
>
> Fix this by open-coding the spinlock initialization, cfr.
> device_pm_init_common() in the internal drivers/base code, and in the
> SuperH early platform code.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Exposed by fw_devlinks changing probe order.
> Masked before due to an unrelated wait context check failure, which
> disabled any further spinlock checks.
> https://lore.kernel.org/linux-acpi/CAMuHMdVL-1RKJ5u-HDVA4F4w_+8yGvQQuJQBcZMsdV4yXzzfcw@mail.gmail.com
> ---
>  drivers/staging/board/board.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/staging/board/board.c b/drivers/staging/board/board.c
> index cb6feb34dd401ae3..604612937f038e92 100644
> --- a/drivers/staging/board/board.c
> +++ b/drivers/staging/board/board.c
> @@ -136,6 +136,7 @@ int __init board_staging_register_clock(const struct board_staging_clk *bsc)
>  static int board_staging_add_dev_domain(struct platform_device *pdev,
>                                         const char *domain)
>  {
> +       struct device *dev = &pdev->dev;
>         struct of_phandle_args pd_args;
>         struct device_node *np;
>
> @@ -148,7 +149,11 @@ static int board_staging_add_dev_domain(struct platform_device *pdev,
>         pd_args.np = np;
>         pd_args.args_count = 0;
>
> -       return of_genpd_add_device(&pd_args, &pdev->dev);
> +       /* Cfr. device_pm_init_common() */

What's Cfr?

> +       spin_lock_init(&dev->power.lock);
> +       dev->power.early_init = true;

Also, I tried looking up, but it's not exactly what this flag
represents other than the fact the spinlock has been initialized?
Which is weird to me. So maybe Rafael can double check this?

-Saravana

> +
> +       return of_genpd_add_device(&pd_args, dev);
>  }
>  #else
>  static inline int board_staging_add_dev_domain(struct platform_device *pdev,
> --
> 2.25.1
>