ACPI: battery: Protect all properties with a separated mutex

The acpi_battery_get_property() callback calls acpi_battery_get_state()
without any lock held. On some devices, it happens that the property
cache has expired before a uevent reaches userspace, triggering
simultaneous attempts to evaluate _BST. See [1] for an analysis to sysrq
stacktraces on one of the these devices.

In a few cases, including when the AML is sleeping or acquiring a mutex,
ACPICA drops the namespace and interpreter locks and allows the
evaluation of _BST to start while another task is still evaluating it.
This could somehow confuse the interpreter and lead to chaos in AML
mutexes on some devices, see [2] for an example.

Not holding the lock is also prone to race conditions, for example:

                CPU0                | 	         CPU1
acpi_battery_get_property()         |
  acpi_battery_get_state()          |
    [update_time expired]           |
    extract_package()               | acpi_battery_get_property()
    battery->update_time = jiffies  |   acpi_battery_get_state()
    kfree()                         |     [up to date]
                                    |   [read capacity_now]
    [fix capacity_now due to quirk] |

where CPU1 gets raw capacity_now before CPU0 fixes it to a meaningful
value.

The existing mutex update_lock is not applicapable for
acpi_battery_get_property(), as some code path could call or wait for
acpi_battery_get_property() while holding update_lock.

Therefore, introduce a mutex called property_lock to protect all
accesses to battery properties, so that acpi_battery_get_property() can
take the advantage of the mutex and synchronize itself. With the mutex,
acpi_battery_get_state() are synchronized in all code paths calling it,
and its cache mechanism can always clamp the frequency of _BST
evaluations according to cache_time.

The helper function acpi_battery_handle_discharging() for quirky devices
has to be inlined due to the change, as the mutex must be unlocked
before calling the expensive power_supply_is_system_supplied() helper
function.

Fixes: 86bfd21a0baf ("ACPI: battery: Drop redundant locking")
Reported-by: Rick <rickk1166@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221065#c85 [1]
Reported-by: Avraham Hollander <anhollander516@gmail.com>
Tested-by: Avraham Hollander <anhollander516@gmail.com>
Closes: https://lore.kernel.org/linux-acpi/CAP1mzZReJCn6df5DwEPu-JCQUyr=Pu1cg5xKCMttWZkHCQtVmQ@mail.gmail.com [2]
Signed-off-by: Rong Zhang <i@rong.moe>
Cc: All applicable <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260809-b4-acpi-battery-notification-v5-1-788d54fa2e35@rong.moe
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

0 files changed, 0 insertions, 0 deletions