Commit 041142d7 authored by Hans de Goede's avatar Hans de Goede Committed by Rafael J. Wysocki
Browse files

ACPI: platform-profile: Fix possible deadlock in platform_profile_remove() 



After a rmmod thinkpad_acpi, lockdep pointed out this possible deadlock:

Our _show and _store sysfs attr functions get called with the kn->active
lock held for the sysfs attr and then take the profile_lock.
sysfs_remove_group() also takes the kn->active lock for the sysfs attr,
so if we call it with the profile_lock held, then we get an ABBA deadlock.

platform_profile_remove() must only be called by drivers which have
first *successfully* called platform_profile_register(). Anything else
is a driver bug. So the check for cur_profile being set before calling
sysfs_remove_group() is not necessary and it can be dropped.

It is safe to call sysfs_remove_group() without holding the profile_lock
since the attr-group group cannot be re-added until after we clear
cur_profile.

Change platform_profile_remove() to only hold the profile_lock while
clearing the cur_profile, fixing the deadlock.

Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 84f9017c

drivers/acpi/platform_profile.c

+2 −6
Original line number Diff line number Diff line
@@ -164,13 +164,9 @@ EXPORT_SYMBOL_GPL(platform_profile_register); 


int platform_profile_remove(void)

{

	mutex_lock(&profile_lock);

	if (!cur_profile) {

		mutex_unlock(&profile_lock);

		return -ENODEV;

	}



	sysfs_remove_group(acpi_kobj, &platform_profile_group);



	mutex_lock(&profile_lock);

	cur_profile = NULL;

	mutex_unlock(&profile_lock);

	return 0;