linux-kernel - Re: [PATCH v3 8/8] mfd: cros_ec: add a dev

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Date:   Tue, 27 Nov 2018 09:29:38 -0800
From:   Guenter Roeck <groeck@...gle.com>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>, kernel@...labora.com,
        Benson Leung <bleung@...omium.org>
Subject: Re: [PATCH v3 8/8] mfd: cros_ec: add a dev_release empty method.

Hi Enric,

On Tue, Nov 27, 2018 at 4:19 AM Enric Balletbo i Serra
<enric.balletbo@...labora.com> wrote:
>
> Devices are required to provide a release method. This patch fixes the
> following WARN():
>
> [   47.218707] ------------[ cut here ]------------
> [   47.223901] Device 'cros_ec' does not have a release() function, it is broken and must be fixed.
> [   47.234430] WARNING: CPU: 0 PID: 3585 at drivers/base/core.c:895 device_release+0x80/0x90
> [   47.243560] Modules linked in: btusb btrtl btintel btbcm bluetooth ecdh_generic [...]
> [   47.323851] CPU: 0 PID: 3585 Comm: rmmod Not tainted 4.20.0-rc2+ #29
> [   47.330947] Hardware name: Google Kevin (DT)
> [   47.335714] pstate: 40000005 (nZcv daif -PAN -UAO)
> [   47.341063] pc : device_release+0x80/0x90
> [   47.345537] lr : device_release+0x80/0x90
> [   47.350001] sp : ffff00000b17bc70
> [   47.353698] x29: ffff00000b17bc70 x28: ffff8000e48e9a80
> [   47.359629] x27: 0000000000000000 x26: 0000000000000000
> [   47.365561] x25: 0000000056000000 x24: 0000000000000015
> [   47.371492] x23: ffff8000f0248060 x22: ffff000000b700a0
> [   47.377414] x21: ffff8000edf56100 x20: ffff8000edd13028
> [   47.383346] x19: ffff8000edd13018 x18: 0000000000000095
> [   47.389278] x17: 0000000000000000 x16: 0000000000000000
> [   47.395209] x15: 0000000000000400 x14: 0000000000000400
> [   47.401131] x13: 00000000000001a7 x12: 0000000000000000
> [   47.407053] x11: 0000000000000001 x10: 0000000000000960
> [   47.412976] x9 : ffff00000b17b9b0 x8 : ffff8000e48ea440
> [   47.418898] x7 : ffff8000ee9090c0 x6 : ffff8000f7d0b0b8
> [   47.424830] x5 : ffff8000f7d0b0b8 x4 : 0000000000000000
> [   47.430752] x3 : ffff8000f7d11e68 x2 : ffff8000e48e9a80
> [   47.436674] x1 : 37d859939c964800 x0 : 0000000000000000
> [   47.442597] Call trace:
> [   47.445324]  device_release+0x80/0x90
> [   47.449414]  kobject_put+0x74/0xe8
> [   47.453210]  device_unregister+0x20/0x30
> [   47.457592]  ec_device_remove+0x34/0x48 [cros_ec_dev]
> [   47.463233]  platform_drv_remove+0x28/0x48
> [   47.467805]  device_release_driver_internal+0x1a8/0x240
> [   47.473630]  driver_detach+0x40/0x80
> [   47.477609]  bus_remove_driver+0x54/0xa8
> [   47.481986]  driver_unregister+0x2c/0x58
> [   47.486355]  platform_driver_unregister+0x10/0x18
> [   47.491599]  cros_ec_dev_exit+0x1c/0x258 [cros_ec_dev]
> [   47.497338]  __arm64_sys_delete_module+0x16c/0x1f8
> [   47.502689]  el0_svc_common+0x84/0xd8
> [   47.506776]  el0_svc_handler+0x2c/0x80
> [   47.510960]  el0_svc+0x8/0xc
> [   47.514171] ---[ end trace 9087279fc8c03450 ]---
>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> ---
>
> Changes in v3: None
> Changes in v2:
> - Fix WARN when unloading. This is new in these series.
>
>  drivers/mfd/cros_ec_dev.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/mfd/cros_ec_dev.c b/drivers/mfd/cros_ec_dev.c
> index 1ba98a32715e..cdb941c6db98 100644
> --- a/drivers/mfd/cros_ec_dev.c
> +++ b/drivers/mfd/cros_ec_dev.c
> @@ -35,9 +35,14 @@
>  #define CROS_MAX_DEV 128
>  static int ec_major;
>
> +static void cros_ec_dev_release(struct device *dev)
> +{
> +}
> +

This tends to be a wrong solution. Problem is that object lifetime is
not necessarily tied to device lifetime. Greg KH (copied) has a much
better understanding of the problem than I do.

Guenter

>  static struct class cros_class = {
>         .owner          = THIS_MODULE,
>         .name           = "chromeos",
> +       .dev_release    = cros_ec_dev_release,
>  };
>
>  /* Basic communication */
> --
> 2.19.1
>