linux-kernel - Re: [PATCH 2/4] platform/x86: xiaomi-wmi: Fix race condition when reporting key events

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Date: Tue, 2 Apr 2024 16:13:30 +0200
From: Armin Wolf <W_Armin@....de>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 hdegoede@...hat.com, ilpo.jarvinen@...ux.intel.com
Cc: corbet@....net, linux-doc@...r.kernel.org,
 platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] platform/x86: xiaomi-wmi: Fix race condition when
 reporting key events

Am 29.03.24 um 02:37 schrieb Kuppuswamy Sathyanarayanan:

> On 3/28/24 5:26 PM, Armin Wolf wrote:
>> Am 28.03.24 um 03:58 schrieb Kuppuswamy Sathyanarayanan:
>>
>>> On 3/27/24 6:23 PM, Armin Wolf wrote:
>>>> Multiple WMI events can be received concurrently, so multiple instances
>>>> of xiaomi_wmi_notify() can be active at the same time. Since the input
>>>> device is shared between those handlers, the key input sequence can be
>>>> disturbed.
>>> Since locking is needed for all notify related calls in all WMI drivers,
>>> is there a generic way to add this support in WMI core driver? Like
>>> defining some common function which will hold the lock and call
>>> driver specific notify handler? I am just thinking aloud.. If it is not
>>> feasible, then it is fine.
>> Hi,
>>
>> actually, not all notify-related calls need locking. It just so happens that
>> input drivers must protect their key sequence, other WMI drivers might not need
>> to use any locking at all.
> Got it.
>
>> I would prefer if the WMI driver does the locking, so it can be optimized for
>> each WMI driver.
> Why not implement this support?

Because different WMI drivers will most certainly have different need when it comes to locking.
Some might want to use a simple mutex, some might want to use a RW-lock, and others might need
something totally different.

Implementing all of this inside the WMI driver core will be difficult.

Thanks,
Armin Wolf

>> Thanks,
>> Armin Wolf
>>
>>>> Fix this by protecting the key input sequence with a mutex.
>>>>
>>>> Compile-tested only.
>>>>
>>>> Fixes: edb73f4f0247 ("platform/x86: wmi: add Xiaomi WMI key driver")
>>>> Signed-off-by: Armin Wolf <W_Armin@....de>
>>>> ---
>>>>    drivers/platform/x86/xiaomi-wmi.c | 18 ++++++++++++++++++
>>>>    1 file changed, 18 insertions(+)
>>>>
>>>> diff --git a/drivers/platform/x86/xiaomi-wmi.c b/drivers/platform/x86/xiaomi-wmi.c
>>>> index 1f5f108d87c0..7efbdc111803 100644
>>>> --- a/drivers/platform/x86/xiaomi-wmi.c
>>>> +++ b/drivers/platform/x86/xiaomi-wmi.c
>>>> @@ -2,8 +2,10 @@
>>>>    /* WMI driver for Xiaomi Laptops */
>>>>
>>>>    #include <linux/acpi.h>
>>>> +#include <linux/device.h>
>>>>    #include <linux/input.h>
>>>>    #include <linux/module.h>
>>>> +#include <linux/mutex.h>
>>>>    #include <linux/wmi.h>
>>>>
>>>>    #include <uapi/linux/input-event-codes.h>
>>>> @@ -20,12 +22,21 @@
>>>>
>>>>    struct xiaomi_wmi {
>>>>        struct input_dev *input_dev;
>>>> +    struct mutex key_lock;    /* Protects the key event sequence */
>>>>        unsigned int key_code;
>>>>    };
>>>>
>>>> +static void xiaomi_mutex_destroy(void *data)
>>>> +{
>>>> +    struct mutex *lock = data;
>>>> +
>>>> +    mutex_destroy(lock);
>>>> +}
>>>> +
>>>>    static int xiaomi_wmi_probe(struct wmi_device *wdev, const void *context)
>>>>    {
>>>>        struct xiaomi_wmi *data;
>>>> +    int ret;
>>>>
>>>>        if (wdev == NULL || context == NULL)
>>>>            return -EINVAL;
>>>> @@ -35,6 +46,11 @@ static int xiaomi_wmi_probe(struct wmi_device *wdev, const void *context)
>>>>            return -ENOMEM;
>>>>        dev_set_drvdata(&wdev->dev, data);
>>>>
>>>> +    mutex_init(&data->key_lock);
>>>> +    ret = devm_add_action_or_reset(&wdev->dev, xiaomi_mutex_destroy, &data->key_lock);
>>>> +    if (ret < 0)
>>>> +        return ret;
>>>> +
>>>>        data->input_dev = devm_input_allocate_device(&wdev->dev);
>>>>        if (data->input_dev == NULL)
>>>>            return -ENOMEM;
>>>> @@ -59,10 +75,12 @@ static void xiaomi_wmi_notify(struct wmi_device *wdev, union acpi_object *dummy)
>>>>        if (data == NULL)
>>>>            return;
>>>>
>>>> +    mutex_lock(&data->key_lock);
>>>>        input_report_key(data->input_dev, data->key_code, 1);
>>>>        input_sync(data->input_dev);
>>>>        input_report_key(data->input_dev, data->key_code, 0);
>>>>        input_sync(data->input_dev);
>>>> +    mutex_unlock(&data->key_lock);
>>>>    }
>>>>
>>>>    static const struct wmi_device_id xiaomi_wmi_id_table[] = {
>>>> --
>>>> 2.39.2
>>>>
>>>>