Re: [PATCH] Revert "mfd: cros_ec: Use devm_kzalloc for private data"

[Guenter Roeck]

On Tue, Dec 4, 2018 at 7:58 AM Enric Balletbo i Serra
<enric.balletbo@xxxxxxxxxxxxx> wrote:
>
> This reverts commit 3aa2177e47878f7e7616da8a2050c44f22301b6e.
>
> That commit triggered a new WARN when unloading the module (see at the
> end of the commit message). When a class_dev is embedded in a structure
> then that class_dev is the thing that controls the lifetime of that
> structure, for that reason device managed allocations can't be used here.
> See Documentation/kobject.txt.
>
> Revert the above patch, so the struct is allocated using kzalloc and we
> have a release function for it that frees the allocated memory, otherwise
> it is broken.
>
>  ------------[ cut here ]------------
>  Device 'cros_ec' does not have a release() function, it is broken and must be fixed.
>  WARNING: CPU: 3 PID: 3675 at drivers/base/core.c:895 device_release+0x80/0x90
>  Modules linked in: btusb btrtl btintel btbcm bluetooth ...
>  CPU: 3 PID: 3675 Comm: rmmod Not tainted 4.20.0-rc4 #76
>  Hardware name: Google Kevin (DT)
>  pstate: 40000005 (nZcv daif -PAN -UAO)
>  pc : device_release+0x80/0x90
>  lr : device_release+0x80/0x90
>  sp : ffff00000c47bc70
>  x29: ffff00000c47bc70 x28: ffff8000e86b0d40
>  x27: 0000000000000000 x26: 0000000000000000
>  x25: 0000000056000000 x24: 0000000000000015
>  x23: ffff8000f0bbf860 x22: ffff000000d320a0
>  x21: ffff8000ee93e100 x20: ffff8000ed931428
>  x19: ffff8000ed931418 x18: 0000000000000020
>  x17: 0000000000000000 x16: 0000000000000000
>  x15: 0000000000000400 x14: 0000000000000143
>  x13: 0000000000000000 x12: 0000000000000400
>  x11: 0000000000000157 x10: 0000000000000960
>  x9 : ffff00000c47b9b0 x8 : ffff8000e86b1700
>  x7 : 0000000000000000 x6 : ffff8000f7d520b8
>  x5 : ffff8000f7d520b8 x4 : 0000000000000000
>  x3 : ffff8000f7d58e68 x2 : ffff8000e86b0d40
>  x1 : 37d859939c964800 x0 : 0000000000000000
>  Call trace:
>   device_release+0x80/0x90
>   kobject_put+0x74/0xe8
>   device_unregister+0x20/0x30
>   ec_device_remove+0x34/0x48 [cros_ec_dev]
>   platform_drv_remove+0x28/0x48
>   device_release_driver_internal+0x1a8/0x240
>   driver_detach+0x40/0x80
>   bus_remove_driver+0x54/0xa8
>   driver_unregister+0x2c/0x58
>   platform_driver_unregister+0x10/0x18
>   cros_ec_dev_exit+0x1c/0x2d8 [cros_ec_dev]
>   __arm64_sys_delete_module+0x16c/0x1f8
>   el0_svc_common+0x84/0xd8
>   el0_svc_handler+0x2c/0x80
>   el0_svc+0x8/0xc
>  ---[ end trace a57c4625f3c60ae8 ]---
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 3aa2177e4787 ("mfd: cros_ec: Use devm_kzalloc for private data")
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>

Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx>

> ---
>
>  drivers/mfd/cros_ec_dev.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mfd/cros_ec_dev.c b/drivers/mfd/cros_ec_dev.c
> index 8f9d6964173e..b99a194ce5a4 100644
> --- a/drivers/mfd/cros_ec_dev.c
> +++ b/drivers/mfd/cros_ec_dev.c
> @@ -263,6 +263,11 @@ static const struct file_operations fops = {
>  #endif
>  };
>
> +static void cros_ec_class_release(struct device *dev)
> +{
> +       kfree(to_cros_ec_dev(dev));
> +}
> +
>  static void cros_ec_sensors_register(struct cros_ec_dev *ec)
>  {
>         /*
> @@ -395,7 +400,7 @@ static int ec_device_probe(struct platform_device *pdev)
>         int retval = -ENOMEM;
>         struct device *dev = &pdev->dev;
>         struct cros_ec_platform *ec_platform = dev_get_platdata(dev);
> -       struct cros_ec_dev *ec = devm_kzalloc(dev, sizeof(*ec), GFP_KERNEL);
> +       struct cros_ec_dev *ec = kzalloc(sizeof(*ec), GFP_KERNEL);
>
>         if (!ec)
>                 return retval;
> @@ -417,6 +422,7 @@ static int ec_device_probe(struct platform_device *pdev)
>         ec->class_dev.devt = MKDEV(ec_major, pdev->id);
>         ec->class_dev.class = &cros_class;
>         ec->class_dev.parent = dev;
> +       ec->class_dev.release = cros_ec_class_release;
>
>         retval = dev_set_name(&ec->class_dev, "%s", ec_platform->ec_name);
>         if (retval) {
> --
> 2.19.1
>