(cc'ing Greg) NeilBrown wrote: > Currently md devices, once created, never disappear until the module > is unloaded. This is essentially because the gendisk holds a > reference to the mddev, and the mddev holds a reference to the > gendisk, this a circular reference. > > If we drop the reference from mddev to gendisk, then we need to ensure > that the mddev is destroyed when the gendisk is destroyed. However it > is not possible to hook into the gendisk destruction process to enable > this. > > So we drop the reference from the gendisk to the mddev and destroy the > gendisk when the mddev gets destroyed. However this has a > complication. > 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. Ah... I'm not really sure I'm following all of this correctly but would it be possible to just add ->release to genhd and do regular reference counting rather than this complex dancing? ->release was recently added to cdev so it'll be nicely parallel. Thanks. -- tejun -- 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
