From: Wolfram Sang <wsa@the-dreams.de>
To: Javier Martinez Canillas <javier@osg.samsung.com>
Cc: linux-kernel@vger.kernel.org, Anand Moon <linux.amoon@gmail.com>,
Kukjin Kim <kgene@kernel.org>,
linux-samsung-soc@vger.kernel.org,
Krzysztof Kozlowski <k.kozlowski@samsung.com>,
linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/2] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared
Date: Fri, 22 Apr 2016 15:31:46 +0200 [thread overview]
Message-ID: <20160422133146.GC1538@katana> (raw)
In-Reply-To: <1460855693-28225-2-git-send-email-javier@osg.samsung.com>
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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
Squashed both patches into one for easier backporting, added stable and
applied to for-current, thanks!
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From: wsa@the-dreams.de (Wolfram Sang)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 2/2] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared
Date: Fri, 22 Apr 2016 15:31:46 +0200 [thread overview]
Message-ID: <20160422133146.GC1538@katana> (raw)
In-Reply-To: <1460855693-28225-2-git-send-email-javier@osg.samsung.com>
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
Squashed both patches into one for easier backporting, added stable and
applied to for-current, thanks!
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next prev parent reply other threads:[~2016-04-22 13:31 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-17 1:14 [PATCH v2 1/2] i2c: exynos5: Check clk_prepare_enable() return value Javier Martinez Canillas
2016-04-17 1:14 ` Javier Martinez Canillas
2016-04-17 1:14 ` [PATCH v2 2/2] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared Javier Martinez Canillas
2016-04-17 1:14 ` Javier Martinez Canillas
2016-04-17 13:34 ` Krzysztof Kozlowski
2016-04-17 13:34 ` Krzysztof Kozlowski
2016-04-22 13:31 ` Wolfram Sang [this message]
2016-04-22 13:31 ` Wolfram Sang
2016-04-17 13:32 ` [PATCH v2 1/2] i2c: exynos5: Check clk_prepare_enable() return value Krzysztof Kozlowski
2016-04-17 13:32 ` Krzysztof Kozlowski
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