Patch "i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
i2c-exynos5-fix-possible-abba-deadlock-by-keeping-i2c-clock-prepared.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Javier Martinez Canillas <[email protected]>
Date: Sat, 16 Apr 2016 21:14:52 -0400
Subject: i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared

From: Javier Martinez Canillas <[email protected]>

commit 10ff4c5239a137abfc896ec73ef3d15a0f86a16a upstream.

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.

---
 drivers/i2c/busses/i2c-exynos5.c |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

@@ -671,7 +671,9 @@ static int exynos5_i2c_xfer(struct i2c_a
 		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_a
 	}
 
  out:
-	clk_disable_unprepare(i2c->clk);
+	clk_disable(i2c->clk);
 	return ret;
 }
 

@@ -747,7 +749,9 @@ static int exynos5_i2c_probe(struct plat
 		return -ENOENT;
 	}
 
-	clk_prepare_enable(i2c->clk);
+	ret = clk_prepare_enable(i2c->clk);
+	if (ret)
+		return ret;
 
 	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	i2c->regs = devm_ioremap_resource(&pdev->dev, mem);

@@ -799,6 +803,10 @@ static int exynos5_i2c_probe(struct plat
 
 	platform_set_drvdata(pdev, i2c);
 
+	clk_disable(i2c->clk);
+
+	return 0;
+
  err_clk:
 	clk_disable_unprepare(i2c->clk);
 	return ret;

@@ -810,6 +818,8 @@ static int exynos5_i2c_remove(struct pla
 
 	i2c_del_adapter(&i2c->adap);
 
+	clk_unprepare(i2c->clk);
+
 	return 0;
 }
 

@@ -821,6 +831,8 @@ static int exynos5_i2c_suspend_noirq(str
 
 	i2c->suspended = 1;
 
+	clk_unprepare(i2c->clk);
+
 	return 0;
 }
 

@@ -830,7 +842,9 @@ static int exynos5_i2c_resume_noirq(stru
 	struct exynos5_i2c *i2c = platform_get_drvdata(pdev);
 	int ret = 0;
 
-	clk_prepare_enable(i2c->clk);
+	ret = clk_prepare_enable(i2c->clk);
+	if (ret)
+		return ret;
 
 	ret = exynos5_hsi2c_clock_setup(i2c);
 	if (ret) {

@@ -839,7 +853,7 @@ static int exynos5_i2c_resume_noirq(stru
 	}
 
 	exynos5_i2c_init(i2c);
-	clk_disable_unprepare(i2c->clk);
+	clk_disable(i2c->clk);
 	i2c->suspended = 0;
 
 	return 0;

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/i2c-exynos5-fix-possible-abba-deadlock-by-keeping-i2c-clock-prepared.patch