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

[Armin Wolf]

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@xxxxxx>
> > > > ---
> > > >    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