linux-kernel - Re: [PATCH V2 3/3] mfd: wm8994-core: Don't use managed regulator bulk get API

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Date:   Fri, 16 Sep 2016 08:38:38 +0100
From:   Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     Lee Jones <lee.jones@...aro.org>, <linaro-kernel@...ts.linaro.org>,
        "Mark Brown" <broonie@...nel.org>,
        Krzysztof Kozłowski <k.kozlowski@...sung.com>,
        <patches@...nsource.wolfsonmicro.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 3/3] mfd: wm8994-core: Don't use managed regulator
 bulk get API

On Fri, Sep 16, 2016 at 08:57:00AM +0530, Viresh Kumar wrote:
> 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>
> 
> ---

Acked-by: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>

Thanks,
Charles