On Sun, Aug 25, 2013 at 10:09:47PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > There are two mutexes, device_hotplug_lock and acpi_scan_lock, held > around the acpi_bus_trim() call in acpi_scan_hot_remove() which > generally removes devices (it removes ACPI device objects at least, > but it may also remove "physical" device objects through .detach() > callbacks of ACPI scan handlers). Thus, potentially, device sysfs > attributes are removed under these locks and to remove those > attributes it is necessary to hold the s_active references of their > directory entries for writing. > > On the other hand, the execution of a .show() or .store() callback > from a sysfs attribute is carried out with that attribute's s_active > reference held for reading. Consequently, if any device sysfs > attribute that may be removed from within acpi_scan_hot_remove() > through acpi_bus_trim() has a .store() or .show() callback which > acquires either acpi_scan_lock or device_hotplug_lock, the execution > of that callback may deadlock with the removal of the attribute. > [Unfortunately, the "online" device attribute of CPUs and memory > blocks and the "eject" attribute of ACPI device objects are affected > by this issue.] > > To avoid those deadlocks introduce a new protection mechanism that > can be used by the device sysfs attributes in question. Namely, > if a device sysfs attribute's .store() or .show() callback routine > is about to acquire device_hotplug_lock or acpi_scan_lock, it can > first execute read_lock_device_remove() and return an error code if > that function returns false. If true is returned, the lock in > question may be acquired and read_unlock_device_remove() must be > called. [This mechanism is implemented by means of an additional > rwsem in drivers/base/core.c.] > > Make the affected sysfs attributes in the driver core and ACPI core > use read_lock_device_remove() and read_unlock_device_remove() as > described above. > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Reported-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx> Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
