Re: [PATCH] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared

[Anand Moon]

Hi Javier,

On 16 April 2016 at 03:34, Javier Martinez Canillas
<javier@xxxxxxxxxxxxxxx> wrote:
> The exynos5 I2C controller driver always prepares and enables a clock
> before using it and then disables unprepares it when the clock is not
> used anymore.
>
> But this can cause a possible ABBA deadlock in some scenarios since a
> driver that uses regmap to access its I2C registers, will first grab
> the regmap lock and then the I2C xfer function will grab the prepare
> lock when preparing the I2C clock. But since the clock driver also
> uses regmap for I2C accesses, preparing a clock will first grab the
> prepare lock and then the regmap lock when using the regmap API.
>
> An example of this happens on the Exynos5422 Odroid XU board where a
> s2mps11 PMIC is used and both the s2mps11 regulators and clk drivers
> share the same I2C regmap.
>
> The possible deadlock is reported by the kernel lockdep:
>
>   Possible unsafe locking scenario:
>
>         CPU0                    CPU1
>         ----                    ----
>    lock(sec_core:428:(regmap)->lock);
>                                 lock(prepare_lock);
>                                 lock(sec_core:428:(regmap)->lock);
>    lock(prepare_lock);
>
>   *** DEADLOCK ***
>
> Fix this by only preparing the clock on probe and {en,dis}able in the
> rest of the driver.
>
> This patch is similar to commit 34e81ad5f0b6 ("i2c: s3c2410: fix ABBA
> deadlock by keeping clock prepared") that fixes the same bug in other
> driver for an I2C controller found in Samsung SoCs.
>
> Reported-by: Anand Moon <linux.amoon@xxxxxxxxx>
> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
>
> ---
>
>  drivers/i2c/busses/i2c-exynos5.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-exynos5.c b/drivers/i2c/busses/i2c-exynos5.c
> index b29c7500461a..602633747149 100644
> --- a/drivers/i2c/busses/i2c-exynos5.c
> +++ b/drivers/i2c/busses/i2c-exynos5.c
> @@ -671,7 +671,9 @@ static int exynos5_i2c_xfer(struct i2c_adapter *adap,
>                 return -EIO;
>         }
>
> -       clk_prepare_enable(i2c->clk);
> +       ret = clk_enable(i2c->clk);
> +       if (ret)
> +               return ret;
>
>         for (i = 0; i < num; i++, msgs++) {
>                 stop = (i == num - 1);
> @@ -695,7 +697,7 @@ static int exynos5_i2c_xfer(struct i2c_adapter *adap,
>         }
>
>   out:
> -       clk_disable_unprepare(i2c->clk);
> +       clk_disable(i2c->clk);
>         return ret;
>  }
>
> @@ -799,6 +801,10 @@ static int exynos5_i2c_probe(struct platform_device *pdev)
>
>         platform_set_drvdata(pdev, i2c);
>
> +       clk_disable(i2c->clk);
> +
> +       return 0;
> +
>   err_clk:
>         clk_disable_unprepare(i2c->clk);
>         return ret;
> @@ -810,6 +816,8 @@ static int exynos5_i2c_remove(struct platform_device *pdev)
>
>         i2c_del_adapter(&i2c->adap);
>
> +       clk_unprepare(i2c->clk);
> +
>         return 0;
>  }
>
> @@ -830,16 +838,18 @@ static int exynos5_i2c_resume_noirq(struct device *dev)
>         struct exynos5_i2c *i2c = platform_get_drvdata(pdev);
>         int ret = 0;
>
> -       clk_prepare_enable(i2c->clk);
> +       ret = clk_enable(i2c->clk);
> +       if (ret)
> +               return ret;
>
>         ret = exynos5_hsi2c_clock_setup(i2c);
>         if (ret) {
> -               clk_disable_unprepare(i2c->clk);
> +               clk_disable(i2c->clk);
>                 return ret;
>         }
>
>         exynos5_i2c_init(i2c);
> -       clk_disable_unprepare(i2c->clk);
> +       clk_disable(i2c->clk);
>         i2c->suspended = 0;
>
>         return 0;
> --
> 2.5.5
>

Thanks for fixing this bug. I also tried the same thing on clk, but
missed the return on failed.

Reviewed-by: Anand Moon <linux.amoon@xxxxxxxxx>
Tested-by: Anand Moon <linux.amoon@xxxxxxxxx>

Best Regards
-Anand Moon