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It's a very common pattern to emit consecutive battery notifications,
for example:
Method (_Qxx, 0, NotSerialized)
{
Notify (BAT0, 0x80) // Status Change
Notify (BAT0, 0x81) // Information Change
}
In this case, the current code path will update battery state twice
within a short period, which is not optimal, as the same data are
fetched twice. Moreover, both notifications are likely to call
power_supply_changed(), causing power_supply_uevent() to read all
battery properties in order to assemble uevents. Even worse, after the
first uevent reaches userspace, some userspace processes start to read
all battery properties in order to refresh their internal states, which
competes with the second notification's handling and uevent assembling.
This generates significant pressure on _STA, _BST and _BIX/_BIF methods.
Not only that, power_supply_ext properties may also rely on some other
ACPI methods, so both uevent assembling and userspace processes call
them. It becomes a nightmare when all these methods share the same ACPI
mutex protecting EC accesses and hence vulnerable to lock starvation.
This is exactly the case of some Lenovo devices, where the mentioned EC
query pattern eventually leads to a catastrophic situation that a bunch
of ACPI methods (including but not limited to the mentioned ones) fail
to acquire the same mutex due to timeout. These devices don't handle
mutex acquisition failure gracefully and return garbage data, causing
even more chaos.
Improve battery notification handling by merging at most 16 consecutive
battery notifications within 10ms using a delayed work, so that they
only refresh and/or update battery state once. ACPI netlink event and
notifier call chain are still triggered multiple times in order not to
break other components. Finally, call power_supply_changed() once and
lead to a single uevent instead of a bunch, preventing userspace
programs from causing too much pressure on power supply properties and
underlying ACPI methods.
If more than 16 battery notifications are queued within 10ms, the
firmware/hardware is anyway buggy, and extra notifications will be
dropped.
Tested-by: Jeffrey Wälti <jeffrey@waelti.dev>
Tested-by: Avraham Hollander <anhollander516@gmail.com>
Reported-by: Rick <rickk1166@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221065
Signed-off-by: Rong Zhang <i@rong.moe>
Link: https://patch.msgid.link/20260718-b4-acpi-battery-notification-v4-1-599c8ed1072f@rong.moe
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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