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Message-ID: <20250923023854.158108-1-luogf2025@163.com>
Date: Tue, 23 Sep 2025 10:38:52 +0800
From: GuangFei Luo <luogf2025@....com>
To: rafael@...nel.org
Cc: dan.carpenter@...aro.org,
lenb@...nel.org,
linux-acpi@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org,
lkp@...el.com,
sre@...nel.org,
stable@...r.kernel.org,
Guofeng Luo <luogf2025@....com>
Subject: Re: [PATCH v6] ACPI: battery: prevent sysfs_add_battery re-entry on rapid events
From: Guofeng Luo <luogf2025@....com>
>On Thu, Sep 18, 2025 at 3:56 PM GuangFei Luo <luogf2025@....com> wrote:
>>
>> When removing and reinserting the laptop battery, ACPI can trigger
>> two notifications in quick succession:
>> - ACPI_BATTERY_NOTIFY_STATUS (0x80)
>> - ACPI_BATTERY_NOTIFY_INFO (0x81)
>>
>> Both notifications call acpi_battery_update(). Because the events
>> happen very close in time, sysfs_add_battery() can be re-entered
>> before battery->bat is set, causing a duplicate sysfs entry error.
>>
>> When the ACPI battery driver uses
>> acpi_dev_install_notify_handler() to register acpi_battery_notify,
>> the callback may be triggered twice in a very short period of time.
>>
>> This patch ensures that sysfs_add_battery() is not re-entered
>> when battery->bat is already non-NULL, preventing the duplicate
>> sysfs creation and stabilizing battery hotplug handling.
>>
>> [ 476.117945] sysfs: cannot create duplicate filename '/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C0A:00/power_supply/BAT1'
>> [ 476.118896] CPU: 1 UID: 0 PID: 185 Comm: kworker/1:4 Kdump: loaded Not tainted 6.12.38+deb13-amd64 #1 Debian 6.12.38-1
>> [ 476.118903] Hardware name: Gateway NV44 /SJV40-MV , BIOS V1.3121 04/08/2009
>> [ 476.118906] Workqueue: kacpi_notify acpi_os_execute_deferred
>> [ 476.118917] Call Trace:
>> [ 476.118922] <TASK>
>> [ 476.118929] dump_stack_lvl+0x5d/0x80
>> [ 476.118938] sysfs_warn_dup.cold+0x17/0x23
>> [ 476.118943] sysfs_create_dir_ns+0xce/0xe0
>> [ 476.118952] kobject_add_internal+0xba/0x250
>> [ 476.118959] kobject_add+0x96/0xc0
>> [ 476.118964] ? get_device_parent+0xde/0x1e0
>> [ 476.118970] device_add+0xe2/0x870
>> [ 476.118975] __power_supply_register.part.0+0x20f/0x3f0
>> [ 476.118981] ? wake_up_q+0x4e/0x90
>> [ 476.118990] sysfs_add_battery+0xa4/0x1d0 [battery]
>> [ 476.118998] acpi_battery_update+0x19e/0x290 [battery]
>> [ 476.119002] acpi_battery_notify+0x50/0x120 [battery]
>> [ 476.119006] acpi_ev_notify_dispatch+0x49/0x70
>> [ 476.119012] acpi_os_execute_deferred+0x1a/0x30
>> [ 476.119015] process_one_work+0x177/0x330
>> [ 476.119022] worker_thread+0x251/0x390
>> [ 476.119026] ? __pfx_worker_thread+0x10/0x10
>> [ 476.119030] kthread+0xd2/0x100
>> [ 476.119033] ? __pfx_kthread+0x10/0x10
>> [ 476.119035] ret_from_fork+0x34/0x50
>> [ 476.119040] ? __pfx_kthread+0x10/0x10
>> [ 476.119042] ret_from_fork_asm+0x1a/0x30
>> [ 476.119049] </TASK>
>> [ 476.142552] kobject: kobject_add_internal failed for BAT1 with -EEXIST, don't try to register things with the same name in the same directory.
>> [ 476.415022] ata1.00: unexpected _GTF length (8)
>> [ 476.428076] sd 0:0:0:0: [sda] Starting disk
>> [ 476.835035] ata1.00: unexpected _GTF length (8)
>> [ 476.839720] ata1.00: configured for UDMA/133
>> [ 491.328831] sysfs: cannot create duplicate filename '/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C0A:00/power_supply/BAT1'
>> [ 491.329720] CPU: 1 UID: 0 PID: 185 Comm: kworker/1:4 Kdump: loaded Not tainted 6.12.38+deb13-amd64 #1 Debian 6.12.38-1
>> [ 491.329727] Hardware name: Gateway NV44 /SJV40-MV , BIOS V1.3121 04/08/2009
>> [ 491.329731] Workqueue: kacpi_notify acpi_os_execute_deferred
>> [ 491.329741] Call Trace:
>> [ 491.329745] <TASK>
>> [ 491.329751] dump_stack_lvl+0x5d/0x80
>> [ 491.329758] sysfs_warn_dup.cold+0x17/0x23
>> [ 491.329762] sysfs_create_dir_ns+0xce/0xe0
>> [ 491.329770] kobject_add_internal+0xba/0x250
>> [ 491.329775] kobject_add+0x96/0xc0
>> [ 491.329779] ? get_device_parent+0xde/0x1e0
>> [ 491.329784] device_add+0xe2/0x870
>> [ 491.329790] __power_supply_register.part.0+0x20f/0x3f0
>> [ 491.329797] sysfs_add_battery+0xa4/0x1d0 [battery]
>> [ 491.329805] acpi_battery_update+0x19e/0x290 [battery]
>> [ 491.329809] acpi_battery_notify+0x50/0x120 [battery]
>> [ 491.329812] acpi_ev_notify_dispatch+0x49/0x70
>> [ 491.329817] acpi_os_execute_deferred+0x1a/0x30
>> [ 491.329820] process_one_work+0x177/0x330
>> [ 491.329826] worker_thread+0x251/0x390
>> [ 491.329830] ? __pfx_worker_thread+0x10/0x10
>> [ 491.329833] kthread+0xd2/0x100
>> [ 491.329836] ? __pfx_kthread+0x10/0x10
>> [ 491.329838] ret_from_fork+0x34/0x50
>> [ 491.329842] ? __pfx_kthread+0x10/0x10
>> [ 491.329844] ret_from_fork_asm+0x1a/0x30
>> [ 491.329850] </TASK>
>> [ 491.329855] kobject: kobject_add_internal failed for BAT1 with -EEXIST, don't try to register things with the same name in the same directory.
>>
>> Fixes: 10666251554c ("ACPI: battery: Install Notify() handler directly")
>> Signed-off-by: GuangFei Luo <luogf2025@....com>
>> Cc: stable@...r.kernel.org
>> ---
>> v6:
>> - Update Fixes tag: point to commit 10666251554c ("ACPI: battery: Install
>> Notify() handler directly"), which introduced the sysfs_add_battery()
>> re-entry issue when acpi_battery_notify is registered via
>> acpi_dev_install_notify_handler(). The problem does not occur with
>> acpi_bus_register_driver().
>>
>> v5:
>> - Move changelog above the '---' line as per submission guidelines.
>>
>> v4:
>> - Uses guard(mutex) for battery->sysfs_lock in sysfs_add_battery().
>> - Since sysfs_add_battery() now handles the battery->bat check with
>> proper locking,the extra if (!battery->bat) check at the call site
>> has become redundant.
>>
>> v3:
>> - Modified the earlier approach: since sysfs_add_battery() is invoked
>> from multiple places, the most reliable way is to add the lock inside
>> the function itself.
>> - sysfs_remove_battery() had a similar race issue in the past, which was
>> fixed by adding a lock as well. Reference:
>> https://lore.kernel.org/all/9c921c22a7f33397a6774d7fa076db9b6a0fd669
>> .1312318300.git.len.brown@...el.com/
>>
>> v2:
>> - Fix missing mutex_unlock in acpi_battery_update()
>> (Reported-by: kernel test robot)
>>
>> v1:
>> - Initial patch to handle race when hotplugging battery, preventing
>> duplicate sysfs entries.
>> ---
>> drivers/acpi/battery.c | 20 +++++++++++---------
>> 1 file changed, 11 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
>> index 6905b56bf3e4..20d68f3e881f 100644
>> --- a/drivers/acpi/battery.c
>> +++ b/drivers/acpi/battery.c
>> @@ -850,6 +850,10 @@ static void __exit battery_hook_exit(void)
>>
>> static int sysfs_add_battery(struct acpi_battery *battery)
>> {
>> + guard(mutex)(&battery->sysfs_lock);
>> + if (battery->bat)
>> + return 0;
>> +
>> struct power_supply_config psy_cfg = {
>> .drv_data = battery,
>> .attr_grp = acpi_battery_groups,
>> @@ -1026,11 +1030,9 @@ static int acpi_battery_update(struct acpi_battery *battery, bool resume)
>> return result;
>> acpi_battery_quirks(battery);
>>
>> - if (!battery->bat) {
>> - result = sysfs_add_battery(battery);
>> - if (result)
>> - return result;
>> - }
>> + result = sysfs_add_battery(battery);
>> + if (result)
>> + return result;
>>
>> /*
>> * Wakeup the system if battery is critical low
>> @@ -1112,12 +1114,12 @@ static int battery_notify(struct notifier_block *nb,
>> result = acpi_battery_get_info(battery);
>> if (result)
>> return result;
>> -
>> - result = sysfs_add_battery(battery);
>> - if (result)
>> - return result;
>> }
>>
>> + result = sysfs_add_battery(battery);
>> + if (result)
>> + return result;
>> +
>
>Why is this change necessary?
Hi Rafael,
In the previous code:
if (battery->bat) {
acpi_battery_refresh(battery);
} else {
result = acpi_battery_get_info(battery);
if (result)
return result;
result = sysfs_add_battery(battery);
if (result)
return result;
}
the `if (!battery->bat)` check was done at the call site. However,
this check is not atomic: two threads can both see `battery->bat == NULL`
and then call `sysfs_add_battery()` concurrently, leading to duplicate
sysfs registration and `-EEXIST` errors.
By moving the check and mutex into `sysfs_add_battery()`, the race is
handled atomically. All call sites can now invoke it unconditionally,
and the function itself will no-op if the battery is already registered.
This avoids duplicated `if (!battery->bat)` logic and ensures consistent
protection everywhere.
Thanks,
GuangFei
>
>> acpi_battery_init_alarm(battery);
>> acpi_battery_get_state(battery);
>> break;
>> --
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