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SubjectRe: [PATCH] Battery: sysfs_remove_battery(): possible circular locking
On (08/05/11 13:10), lan,Tianyu wrote:
> I think changing 'the marker' to 'battery->bat.name' will introduce
> problem.
> In the sysfs_add_battery(), when the 'battery->bat.name' is assigned,
> the power_supply_register() and device_create_file() have not been
> invoked. In this time, maybe sysfs_remove_battery() will be invoked and
> cause device_remove_file() and power_supply_unregister() invoked without
> device file created and power supply registered.
>
> sysfs_remove_battery() will be invoked in the battery_notify(),
> acpi_battery_refresh() and sysfs_remove_battery() which causes the
> situation. This is also the cause of bug 35642.
>

Well, how about using separate (independent lock) for sysfs_remove_battery()
case? Since we can't safely drop battery->lock in sysfs_remove_battery() before
power_supply_unregister() call.

Not sure if it should be within struct acpi_battery, perhaps we could
have it as a 'global' battery lock. Anyway, here it is:

---
drivers/acpi/battery.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 87c0a8d..7711d94 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -99,6 +99,7 @@ enum {

struct acpi_battery {
struct mutex lock;
+ struct mutex sysfs_lock;
struct power_supply bat;
struct acpi_device *device;
struct notifier_block pm_nb;
@@ -573,16 +574,16 @@ static int sysfs_add_battery(struct acpi_battery *battery)

static void sysfs_remove_battery(struct acpi_battery *battery)
{
- mutex_lock(&battery->lock);
+ mutex_lock(&battery->sysfs_lock);
if (!battery->bat.dev) {
- mutex_unlock(&battery->lock);
+ mutex_unlock(&battery->sysfs_lock);
return;
}

device_remove_file(battery->bat.dev, &alarm_attr);
power_supply_unregister(&battery->bat);
battery->bat.dev = NULL;
- mutex_unlock(&battery->lock);
+ mutex_unlock(&battery->sysfs_lock);
}

/*
@@ -982,6 +983,7 @@ static int acpi_battery_add(struct acpi_device *device)
strcpy(acpi_device_class(device), ACPI_BATTERY_CLASS);
device->driver_data = battery;
mutex_init(&battery->lock);
+ mutex_init(&battery->sysfs_lock);
if (ACPI_SUCCESS(acpi_get_handle(battery->device->handle,
"_BIX", &handle)))
set_bit(ACPI_BATTERY_XINFO_PRESENT, &battery->flags);
@@ -1010,6 +1012,7 @@ static int acpi_battery_add(struct acpi_device *device)
fail:
sysfs_remove_battery(battery);
mutex_destroy(&battery->lock);
+ mutex_destroy(&battery->sysfs_lock);
kfree(battery);
return result;
}
@@ -1027,6 +1030,7 @@ static int acpi_battery_remove(struct acpi_device *device, int type)
#endif
sysfs_remove_battery(battery);
mutex_destroy(&battery->lock);
+ mutex_destroy(&battery->sysfs_lock);
kfree(battery);
return 0;
}


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