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

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Date: Fri, 29 Mar 2024 01:26:26 +0100
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 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.

I would prefer if the WMI driver does the locking, so it can be optimized for
each WMI driver.

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
>>
>>