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From:   Todd Kjos <tkjos@android.com>
Date:   Wed, 25 Apr 2018 08:56:09 -0700
Message-ID: <CAD0t5oPbMFMgxvePX=qu3aq-L0nPqwC9MJmyXoQRaW85+HK75w@mail.gmail.com>
Subject: Re: [PATCH v2 2/4] ARM: amba: Fix race condition with driver_override
To:     Geert Uytterhoeven <geert+renesas@glider.be>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Russell King <linux@armlinux.org.uk>,
        Adrian Salido <salidoa@google.com>,
        Nicolai Stange <nstange@suse.de>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        LKML <linux-kernel@vger.kernel.org>
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Reviewed-by: Todd Kjos <tkjos@android.com>

On Tue, Apr 10, 2018 at 6:21 AM, Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> The driver_override implementation is susceptible to a race condition
> when different threads are reading vs storing a different driver
> override.  Add locking to avoid this race condition.
>
> Cfr. commits 6265539776a0810b ("driver core: platform: fix race
> condition with driver_override") and 9561475db680f714 ("PCI: Fix race
> condition with driver_override").
>
> Fixes: 3cf385713460eb2b ("ARM: 8256/1: driver coamba: add device binding path 'driver_override'")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>  drivers/amba/bus.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 6ffd778352e6d953..36c5653ced5742b7 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -69,8 +69,12 @@ static ssize_t driver_override_show(struct device *_dev,
>                                     struct device_attribute *attr, char *buf)
>  {
>         struct amba_device *dev = to_amba_device(_dev);
> +       ssize_t len;
>
> -       return sprintf(buf, "%s\n", dev->driver_override);
> +       device_lock(_dev);
> +       len = sprintf(buf, "%s\n", dev->driver_override);
> +       device_unlock(_dev);
> +       return len;
>  }
>
>  static ssize_t driver_override_store(struct device *_dev,
> @@ -78,7 +82,7 @@ static ssize_t driver_override_store(struct device *_dev,
>                                      const char *buf, size_t count)
>  {
>         struct amba_device *dev = to_amba_device(_dev);
> -       char *driver_override, *old = dev->driver_override, *cp;
> +       char *driver_override, *old, *cp;
>
>         if (count > PATH_MAX)
>                 return -EINVAL;
> @@ -91,12 +95,15 @@ static ssize_t driver_override_store(struct device *_dev,
>         if (cp)
>                 *cp = '\0';
>
> +       device_lock(_dev);
> +       old = dev->driver_override;
>         if (strlen(driver_override)) {
>                 dev->driver_override = driver_override;
>         } else {
>                kfree(driver_override);
>                dev->driver_override = NULL;
>         }
> +       device_unlock(_dev);
>
>         kfree(old);
>
> --
> 2.7.4
>