On Wed, Aug 28, 2013 at 03:48:11PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > device_hotplug_lock is 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 that > lock 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 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 is one of them.] > > To avoid such deadlocks, make all of the sysfs attribute callbacks > that need to lock device hotplug, for example store_online(), use > a special function, lock_device_hotplug_sysfs(), to lock device > hotplug and return the result of that function immediately if it is > not zero. This will cause the s_active reference of the directory > entry in question to be released and the syscall to be restarted > if device_hotplug_lock cannot be acquired. > > [show_online() actually doesn't need to lock device hotplug, but > it is useful to serialize it with respect to device_offline() and > device_online() for the same device (in case user space attempts to > run them concurrently) which can be done with the help of > device_lock().] > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Reported-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> > 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
