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Message-ID: <CAJZ5v0htRTTj1QEEmhxBDxYA8oXkg_KP5YrfwyngELDY+Ns1EQ@mail.gmail.com>
Date: Wed, 24 Sep 2025 12:40:13 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: GuangFei Luo <luogf2025@....com>
Cc: rafael@...nel.org, dan.carpenter@...aro.org, linux-acpi@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v6] ACPI: battery: prevent sysfs_add_battery re-entry on
rapid events
On Wed, Sep 24, 2025 at 12:38 AM GuangFei Luo <luogf2025@....com> wrote:
>
> > 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@....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.
Please just verify and I'll add a changelog and subject to the patch
and submit it.
Thanks!
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