Message-Id: <00005c8c0b1294412c543604cb537622d6257416.1473996370.git.viresh.kumar@linaro.org>
Date:   Fri, 16 Sep 2016 08:57:00 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     linaro-kernel@...ts.linaro.org, Mark Brown <broonie@...nel.org>,
        Krzysztof Kozłowski <k.kozlowski@...sung.com>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        patches@...nsource.wolfsonmicro.com, linux-kernel@...r.kernel.org
Subject: [PATCH V2 3/3] mfd: wm8994-core: Don't use managed regulator bulk get API

The kernel WARNs and then crashes today if wm8994_device_init() fails
after calling devm_regulator_bulk_get().

That happens because there are multiple devices involved here and the
order in which managed resources are freed isn't correct.

The regulators are added as children of wm8994->dev.  Whereas,
devm_regulator_bulk_get() receives wm8994->dev as the device, though it
gets the same regulators which were added as children of wm8994->dev
earlier.

During failures, the children are removed first and the core eventually
calls regulator_unregister() for them. As regulator_put() was never done
for them (opposite of devm_regulator_bulk_get()), the kernel WARNs at

	WARN_ON(rdev->open_count);

And eventually it crashes from debugfs_remove_recursive().

--------x------------------x----------------

 wm8994 3-001a: Device is not a WM8994, ID is 0
 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 1 at /mnt/ssd/all/work/repos/devel/linux/drivers/regulator/core.c:4072 regulator_unregister+0xc8/0xd0
 Modules linked in:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc6-00154-g54fe84cbd50b #41
 Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
 [<c010e24c>] (unwind_backtrace) from [<c010af38>] (show_stack+0x10/0x14)
 [<c010af38>] (show_stack) from [<c032a1c4>] (dump_stack+0x88/0x9c)
 [<c032a1c4>] (dump_stack) from [<c011a98c>] (__warn+0xe8/0x100)
 [<c011a98c>] (__warn) from [<c011aa54>] (warn_slowpath_null+0x20/0x28)
 [<c011aa54>] (warn_slowpath_null) from [<c0384a0c>] (regulator_unregister+0xc8/0xd0)
 [<c0384a0c>] (regulator_unregister) from [<c0406434>] (release_nodes+0x16c/0x1dc)
 [<c0406434>] (release_nodes) from [<c04039c4>] (__device_release_driver+0x8c/0x110)
 [<c04039c4>] (__device_release_driver) from [<c0403a64>] (device_release_driver+0x1c/0x28)
 [<c0403a64>] (device_release_driver) from [<c0402b24>] (bus_remove_device+0xd8/0x104)
 [<c0402b24>] (bus_remove_device) from [<c03ffcd8>] (device_del+0x10c/0x218)
 [<c03ffcd8>] (device_del) from [<c0404e4c>] (platform_device_del+0x1c/0x88)
 [<c0404e4c>] (platform_device_del) from [<c0404ec4>] (platform_device_unregister+0xc/0x20)
 [<c0404ec4>] (platform_device_unregister) from [<c0428bc0>] (mfd_remove_devices_fn+0x5c/0x64)
 [<c0428bc0>] (mfd_remove_devices_fn) from [<c03ff9d8>] (device_for_each_child_reverse+0x4c/0x78)
 [<c03ff9d8>] (device_for_each_child_reverse) from [<c04288c4>] (mfd_remove_devices+0x20/0x30)
 [<c04288c4>] (mfd_remove_devices) from [<c042758c>] (wm8994_device_init+0x2ac/0x7f0)
 [<c042758c>] (wm8994_device_init) from [<c04f14a8>] (i2c_device_probe+0x178/0x1fc)
 [<c04f14a8>] (i2c_device_probe) from [<c04036fc>] (driver_probe_device+0x214/0x2c0)
 [<c04036fc>] (driver_probe_device) from [<c0403854>] (__driver_attach+0xac/0xb0)
 [<c0403854>] (__driver_attach) from [<c0401a74>] (bus_for_each_dev+0x68/0x9c)
 [<c0401a74>] (bus_for_each_dev) from [<c0402cf0>] (bus_add_driver+0x1a0/0x218)
 [<c0402cf0>] (bus_add_driver) from [<c040406c>] (driver_register+0x78/0xf8)
 [<c040406c>] (driver_register) from [<c04f20a0>] (i2c_register_driver+0x34/0x84)
 [<c04f20a0>] (i2c_register_driver) from [<c01017d0>] (do_one_initcall+0x40/0x170)
 [<c01017d0>] (do_one_initcall) from [<c0a00dbc>] (kernel_init_freeable+0x15c/0x1fc)
 [<c0a00dbc>] (kernel_init_freeable) from [<c06e07b0>] (kernel_init+0x8/0x114)
 [<c06e07b0>] (kernel_init) from [<c0107978>] (ret_from_fork+0x14/0x3c)
 ---[ end trace 0919d3d0bc998260 ]---

 [snip..]

 Unable to handle kernel NULL pointer dereference at virtual address 00000078
 pgd = c0004000
 [00000078] *pgd=00000000
 Internal error: Oops: 5 [#1] PREEMPT SMP ARM
 Modules linked in:
 CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W       4.8.0-rc6-00154-g54fe84cbd50b #41
 Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
 task: ee874000 task.stack: ee878000
 PC is at down_write+0x14/0x54
 LR is at debugfs_remove_recursive+0x30/0x150

 [snip..]

 [<c06e489c>] (down_write) from [<c02e9954>] (debugfs_remove_recursive+0x30/0x150)
 [<c02e9954>] (debugfs_remove_recursive) from [<c0382b78>] (_regulator_put+0x24/0xac)
 [<c0382b78>] (_regulator_put) from [<c0382c1c>] (regulator_put+0x1c/0x2c)
 [<c0382c1c>] (regulator_put) from [<c0406434>] (release_nodes+0x16c/0x1dc)
 [<c0406434>] (release_nodes) from [<c04035d4>] (driver_probe_device+0xec/0x2c0)
 [<c04035d4>] (driver_probe_device) from [<c0403854>] (__driver_attach+0xac/0xb0)
 [<c0403854>] (__driver_attach) from [<c0401a74>] (bus_for_each_dev+0x68/0x9c)
 [<c0401a74>] (bus_for_each_dev) from [<c0402cf0>] (bus_add_driver+0x1a0/0x218)
 [<c0402cf0>] (bus_add_driver) from [<c040406c>] (driver_register+0x78/0xf8)
 [<c040406c>] (driver_register) from [<c04f20a0>] (i2c_register_driver+0x34/0x84)
 [<c04f20a0>] (i2c_register_driver) from [<c01017d0>] (do_one_initcall+0x40/0x170)
 [<c01017d0>] (do_one_initcall) from [<c0a00dbc>] (kernel_init_freeable+0x15c/0x1fc)
 [<c0a00dbc>] (kernel_init_freeable) from [<c06e07b0>] (kernel_init+0x8/0x114)
 [<c06e07b0>] (kernel_init) from [<c0107978>] (ret_from_fork+0x14/0x3c)
 Code: e1a04000 f590f000 e3a03001 e34f3fff (e1902f9f)
 ---[ end trace 0919d3d0bc998262 ]---

--------x------------------x----------------

Fix the kernel warnings and crashes by using regulator_bulk_get()
instead of devm_regulator_bulk_get() and explicitly freeing the supplies
in exit paths.

Tested on Exynos 5250, dual core ARM A15 machine.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

---
V1->V2:
- Use regulator_bulk_free() instead of open coding it.
- Shorter backtrace
- Reworded the last paragraph to make it more clear
- Added a comment in code
---
 drivers/mfd/wm8994-core.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/mfd/wm8994-core.c b/drivers/mfd/wm8994-core.c
index 95e6bc55adbb..953d0790ffd5 100644
--- a/drivers/mfd/wm8994-core.c
+++ b/drivers/mfd/wm8994-core.c
@@ -393,8 +393,13 @@ static int wm8994_device_init(struct wm8994 *wm8994, int irq)
 		BUG();
 		goto err;
 	}
-		
-	ret = devm_regulator_bulk_get(wm8994->dev, wm8994->num_supplies,
+
+	/*
+	 * Can't use devres helper here as some of the supplies are provided by
+	 * wm8994->dev's children (regulators) and those regulators are
+	 * unregistered by the devres core before the supplies are freed.
+	 */
+	ret = regulator_bulk_get(wm8994->dev, wm8994->num_supplies,
 				 wm8994->supplies);
 	if (ret != 0) {
 		dev_err(wm8994->dev, "Failed to get supplies: %d\n", ret);
@@ -404,7 +409,7 @@ static int wm8994_device_init(struct wm8994 *wm8994, int irq)
 	ret = regulator_bulk_enable(wm8994->num_supplies, wm8994->supplies);
 	if (ret != 0) {
 		dev_err(wm8994->dev, "Failed to enable supplies: %d\n", ret);
-		goto err;
+		goto err_regulator_free;
 	}
 
 	ret = wm8994_reg_read(wm8994, WM8994_SOFTWARE_RESET);
@@ -595,6 +600,8 @@ static int wm8994_device_init(struct wm8994 *wm8994, int irq)
 err_enable:
 	regulator_bulk_disable(wm8994->num_supplies,
 			       wm8994->supplies);
+err_regulator_free:
+	regulator_bulk_free(wm8994->num_supplies, wm8994->supplies);
 err:
 	mfd_remove_devices(wm8994->dev);
 	return ret;
@@ -605,6 +612,7 @@ static void wm8994_device_exit(struct wm8994 *wm8994)
 	pm_runtime_disable(wm8994->dev);
 	wm8994_irq_exit(wm8994);
 	regulator_bulk_disable(wm8994->num_supplies, wm8994->supplies);
+	regulator_bulk_free(wm8994->num_supplies, wm8994->supplies);
 	mfd_remove_devices(wm8994->dev);
 }
 
-- 
2.7.1.410.g6faf27b

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