On Mon, Nov 24, 2008 at 02:55:30PM +1100, NeilBrown wrote: > Between the call > __blkdev_get->get_gendisk->kobj_lookup->md_probe > and the call > __blkdev_get->md_open > > there is no obvious way to hold a reference on the mddev any more, so > unless something is done, it will disappear and gendisk will be > destroyed prematurely. > > Also, once we decide to destroy the mddev, there will be an unlockable > moment before the gendisk is unlinked (blk_unregister_region) during > which a new reference to the gendisk can be created. We need to > ensure that this reference can not be used. i.e. the ->open must > fail. > > So: > 1/ in md_probe we set a flag in the mddev (hold_active) which > indicates that the array should be treated as active, even > though there are no references, and no appearance of activity. > This is cleared by md_release when the device is closed. > This ensure that the gendisk will survive between md_probe and > md_open. That won't work. Note that you are not guaranteed that md_release() will be called after md_probe(); there are failure exits in __blkdev_get() that do not reach ->open() at all. What lifetime rules do you really want? I never liked the tricks pulled by md wrt gendisk lifetimes and that might be a good time to sort that out for good... What should happen to things like pending IO, etc. on array destruction? AFAICS, that's the real question... -- 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
