Re:[PATCH v6] ACPI: battery: prevent sysfs_add_battery re-entry on rapid events

[GuangFei Luo <luogf2025@163.com>]

> On Tuesday, September 23, 2025 7:12:03 PM CEST Rafael J. Wysocki wrote:
> > On Tue, Sep 23, 2025 at 6:14 PM GuangFei Luo <luogf2025@163.com> wrote:
> > >
> > > The functions battery_hook_add_battery(), battery_hook_remove_battery(),
> > > and sysfs_remove_battery() already acquire locks, so their internal
> > > accesses are safe.
> > 
> > In fact, there are two locks in use, battery->sysfs_lock and
> > hook_mutex.  The latter is used for managing hooks and the former is
> > only used by sysfs_remove_battery(), so it only prevents that function
> > from racing with another instance of itself.
> > 
> > I would suggest using battery->sysfs_lock for protecting battery->bat
> > in general.
> > 
> > > acpi_battery_refresh() does check battery->bat, but its child
> > > functions (sysfs_add_battery() and sysfs_remove_battery()) already
> > > handle locking.
> > 
> > What locking?  Before the $subject patch, sysfs_add_battery() doesn't
> > do any locking at all AFAICS.
> > 
> > > In acpi_battery_notify(), battery->bat has no lock. However, the
> > > check of battery->bat is at the very end of the function. During
> > > earlier calls, battery->bat has already been protected by locks, so
> > > re-entry will not cause issues.
> > 
> > All of the battery->bat checks and the code depending on them need to
> > go under the same lock.  I'd use battery->sysfs_lock for this as
> > already mentioned above.
> 
> So my (untested) version of this fix is appended.
> 
> Note that it explicitly prevents acpi_battery_notify() from racing with
> addition/removal, PM notifications, and resume.
> 
> ---
>  drivers/acpi/battery.c |   36 +++++++++++++++++++++++-------------
>  1 file changed, 23 insertions(+), 13 deletions(-)
> 
> --- a/drivers/acpi/battery.c
> +++ b/drivers/acpi/battery.c
> @@ -92,7 +92,7 @@ enum {
>  
>  struct acpi_battery {
>  	struct mutex lock;
> -	struct mutex sysfs_lock;
> +	struct mutex update_lock;
>  	struct power_supply *bat;
>  	struct power_supply_desc bat_desc;
>  	struct acpi_device *device;
> @@ -904,15 +904,12 @@ static int sysfs_add_battery(struct acpi
>  
>  static void sysfs_remove_battery(struct acpi_battery *battery)
>  {
> -	mutex_lock(&battery->sysfs_lock);
> -	if (!battery->bat) {
> -		mutex_unlock(&battery->sysfs_lock);
> +	if (!battery->bat)
>  		return;
> -	}
> +
>  	battery_hook_remove_battery(battery);
>  	power_supply_unregister(battery->bat);
>  	battery->bat = NULL;
> -	mutex_unlock(&battery->sysfs_lock);
>  }
>  
>  static void find_battery(const struct dmi_header *dm, void *private)
> @@ -1072,6 +1069,9 @@ static void acpi_battery_notify(acpi_han
>  
>  	if (!battery)
>  		return;
> +
> +	guard(mutex)(&battery->update_lock);
> +
>  	old = battery->bat;
>  	/*
>  	 * On Acer Aspire V5-573G notifications are sometimes triggered too
> @@ -1094,21 +1094,22 @@ static void acpi_battery_notify(acpi_han
>  }
>  
>  static int battery_notify(struct notifier_block *nb,
> -			       unsigned long mode, void *_unused)
> +			  unsigned long mode, void *_unused)
>  {
>  	struct acpi_battery *battery = container_of(nb, struct acpi_battery,
>  						    pm_nb);
> -	int result;
>  
> -	switch (mode) {
> -	case PM_POST_HIBERNATION:
> -	case PM_POST_SUSPEND:
> +	if (mode == PM_POST_SUSPEND || mode == PM_POST_HIBERNATION) {
> +		guard(mutex)(&battery->update_lock);
> +
>  		if (!acpi_battery_present(battery))
>  			return 0;
>  
>  		if (battery->bat) {
>  			acpi_battery_refresh(battery);
>  		} else {
> +			int result;
> +
>  			result = acpi_battery_get_info(battery);
>  			if (result)
>  				return result;
> @@ -1120,7 +1121,6 @@ static int battery_notify(struct notifie
>  
>  		acpi_battery_init_alarm(battery);
>  		acpi_battery_get_state(battery);
> -		break;
>  	}
>  
>  	return 0;
> @@ -1198,6 +1198,8 @@ static int acpi_battery_update_retry(str
>  {
>  	int retry, ret;
>  
> +	guard(mutex)(&battery->update_lock);
> +
>  	for (retry = 5; retry; retry--) {
>  		ret = acpi_battery_update(battery, false);
>  		if (!ret)
> @@ -1230,7 +1232,7 @@ static int acpi_battery_add(struct acpi_
>  	if (result)
>  		return result;
>  
> -	result = devm_mutex_init(&device->dev, &battery->sysfs_lock);
> +	result = devm_mutex_init(&device->dev, &battery->update_lock);
>  	if (result)
>  		return result;
>  
> @@ -1262,6 +1264,8 @@ fail_pm:
>  	device_init_wakeup(&device->dev, 0);
>  	unregister_pm_notifier(&battery->pm_nb);
>  fail:
> +	guard(mutex)(&battery->update_lock);
> +
>  	sysfs_remove_battery(battery);
>  
>  	return result;
> @@ -1281,6 +1285,9 @@ static void acpi_battery_remove(struct a
>  
>  	device_init_wakeup(&device->dev, 0);
>  	unregister_pm_notifier(&battery->pm_nb);
> +
> +	guard(mutex)(&battery->update_lock);
> +
>  	sysfs_remove_battery(battery);
>  }
>  
> @@ -1297,6 +1304,9 @@ static int acpi_battery_resume(struct de
>  		return -EINVAL;
>  
>  	battery->update_time = 0;
> +
> +	guard(mutex)(&battery->update_lock);
> +
>  	acpi_battery_update(battery, true);
>  	return 0;
>  }

Thanks for the detailed explanation and the updated version of the fix.

I will test your suggested changes on my platform.  
After verification, I will send a v7 based on your suggestion.