Since I can remember DM has forced the block layer to allow the allocation and initialization of the request_queue to be distinct operations. Reason for this was block/genhd.c:add_disk() has required that the request_queue (and associated bdi) be tied to the gendisk before add_disk() is called -- because add_disk() also deals with exposing the request_queue via blk_register_queue().
DM's dynamic creation of arbitrary device types (and associated request_queue types) requires the DM device's gendisk be available so that DM table loads can establish a master/slave relationship with subordinate devices that are referenced by loaded DM tables -- using bd_link_disk_holder(). But until these DM tables, and their associated subordinate devices, are known DM cannot know what type of request_queue it needs -- nor what its queue_limits should be. This chicken and egg scenario has created all manner of problems for DM and, at times, the block layer. Summary of changes: - Adjust device_add_disk() so that that it can cope with the gendisk _not_ having its 'queue' established yet. - Remove del_gendisk()'s WARN_ON() if disk->queue is NULL - Move "bdi" symlink creation from register_disk() to the end of blk_register_queue() -- it is more logical in that the bdi is part of the request_queue. - Move extra request_queue reference count (on behalf of gendisk) from device_add_disk() to end of blk_register_queue(). - Make device_add_disk()'s calls to bdi_register_owner() and blk_register_queue() conditional on disk->queue not being NULL. - Export blk_register_queue() These changes allow DM to use device_add_disk() to anchor its gendisk as the "master" for master/slave relationships DM must establish with subordinate devices referenced in DM tables that get loaded. Once all "slave" devices for a DM device are known a request_queue can be properly initialized and then advertised via sysfs -- important improvement being that no request_queue resource initialization is missed. These changes have been tested to work without any IO races because the request_queue and associated bdi don't even exist at the time that the gendisk's "struct device"s are established by device_add_disk(). I've been mindful of historic bugs, and haven't experienced them with DM, e.g.: https://bugzilla.kernel.org/show_bug.cgi?id=16312 (fixed by commit 01ea5063 "block: Fix race during disk initialization") Signed-off-by: Mike Snitzer <[email protected]> --- block/blk-sysfs.c | 12 ++++++++++++ block/genhd.c | 28 ++++++++-------------------- 2 files changed, 20 insertions(+), 20 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 870484eaed1f..0b0dda8e2420 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -919,8 +919,20 @@ int blk_register_queue(struct gendisk *disk) ret = 0; unlock: mutex_unlock(&q->sysfs_lock); + + /* + * Take an extra ref on queue which will be put on disk_release() + * so that it sticks around as long as @disk is there. + */ + WARN_ON_ONCE(!blk_get_queue(q)); + + WARN_ON(sysfs_create_link(&dev->kobj, + &q->backing_dev_info->dev->kobj, + "bdi")); + return ret; } +EXPORT_SYMBOL_GPL(blk_register_queue); void blk_unregister_queue(struct gendisk *disk) { diff --git a/block/genhd.c b/block/genhd.c index 96a66f671720..13aa80319b3b 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -621,11 +621,6 @@ static void register_disk(struct device *parent, struct gendisk *disk) while ((part = disk_part_iter_next(&piter))) kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD); disk_part_iter_exit(&piter); - - err = sysfs_create_link(&ddev->kobj, - &disk->queue->backing_dev_info->dev->kobj, - "bdi"); - WARN_ON(err); } /** @@ -671,24 +666,19 @@ void device_add_disk(struct device *parent, struct gendisk *disk) disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO; disk->flags |= GENHD_FL_NO_PART_SCAN; } else { - int ret; - - /* Register BDI before referencing it from bdev */ disk_to_dev(disk)->devt = devt; - ret = bdi_register_owner(disk->queue->backing_dev_info, - disk_to_dev(disk)); - WARN_ON(ret); + /* Register BDI before referencing it from bdev */ + if (disk->queue) { + retval = bdi_register_owner(disk->queue->backing_dev_info, + disk_to_dev(disk)); + WARN_ON(retval); + } blk_register_region(disk_devt(disk), disk->minors, NULL, exact_match, exact_lock, disk); } register_disk(parent, disk); - blk_register_queue(disk); - - /* - * Take an extra ref on queue which will be put on disk_release() - * so that it sticks around as long as @disk is there. - */ - WARN_ON_ONCE(!blk_get_queue(disk->queue)); + if (disk->queue) + blk_register_queue(disk); disk_add_events(disk); blk_integrity_add(disk); @@ -727,8 +717,6 @@ void del_gendisk(struct gendisk *disk) */ bdi_unregister(disk->queue->backing_dev_info); blk_unregister_queue(disk); - } else { - WARN_ON(1); } if (!(disk->flags & GENHD_FL_HIDDEN)) -- 2.15.0
