Re: [PATCH v2 2/2] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared

[Krzysztof Kozlowski]

On Sat, Apr 16, 2016 at 09:14:53PM -0400, Javier Martinez Canillas 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 XU4 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 it by leaving the code prepared on probe and use {en,dis}able in
> the I2C transfer function.
> 
> 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>
> Reviewed-by: Anand Moon <linux.amoon@xxxxxxxxx>
> Tested-by: Anand Moon <linux.amoon@xxxxxxxxx>
> 
> ---
> 
> Changes in v2:
> - Add Anand Moon's Reviewed and Tested by tags.
> - Unprepare the clock on suspend. Suggested by Krzysztof Kozlowski.
> 
>  drivers/i2c/busses/i2c-exynos5.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)



Hi,

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>

Best regards,
Krzysztof