On Monday January 14, viro@xxxxxxxxxxxxxxxxxx wrote: > On Mon, Jan 14, 2008 at 12:45:31PM +1100, NeilBrown wrote: > > > > Due to possible deadlock issues we need to use a schedule work to > > kobject_del an 'rdev' object from a different thread. > > > > A recent change means that kobject_add no longer gets a refernce, and > > kobject_del doesn't put a reference. Consequently, we need to > > explicitly hold a reference to ensure that the last reference isn't > > dropped before the scheduled work get a chance to call kobject_del. > > > > Also, rename delayed_delete to md_delayed_delete to that it is more > > obvious in a stack trace which code is to blame. > > I don't know... You still get kobject_del() and export_rdev() > in unpredictable order; sure, it won't be freed under you, but... I cannot see that that would matter. kobject_del deletes the object from the kobj tree and free sysfs. export_rdev disconnects the objects from md structures and releases the connection with the device. They are quite independent. > > What is that deadlock problem, anyway? I don't see anything that > would look like an obvious candidate in the stuff you are delaying... Maybe it isn't there any more.... Once upon a time, when I echo remove > /sys/block/mdX/md/dev-YYY/state sysfs_write_file would hold buffer->sem while calling my store handler. When my store handler tried to delete the relevant kobject, it would eventually call orphan_all_buffers which would try to take buf->sem and deadlock. orphan_all_buffers doesn't exist any more, so maybe the deadlock is gone too. However the comment at the top of sysfs_schedule_callback in sysfs/file.c says: * * sysfs attribute methods must not unregister themselves or their parent * kobject (which would amount to the same thing). Attempts to do so will * deadlock, since unregistration is mutually exclusive with driver * callbacks. * so I'm included to leave the code as it is.... ofcourse the comment could be well out of date. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
