[dm-devel] [for-4.16 PATCH v2 2/3] block: cope with gendisk's 'queue' being added later
Mike Snitzer
snitzer at redhat.com
Wed Jan 10 02:41:03 UTC 2018
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.
- 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()
- Move "bdi" symlink removal and bdi_unregister() from del_gendisk() to
blk_unregister_queue(). Suggested by Bart.
- Remove del_gendisk()'s WARN_ON() if disk->queue is NULL
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 <snitzer at redhat.com>
---
block/blk-sysfs.c | 23 ++++++++++++++++++++++-
block/genhd.c | 39 +++++++++------------------------------
2 files changed, 31 insertions(+), 31 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 870484eaed1f..d888ecb95a2a 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -919,8 +919,21 @@ 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));
+
+ if (!(disk->flags & GENHD_FL_HIDDEN))
+ 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)
{
@@ -929,13 +942,21 @@ void blk_unregister_queue(struct gendisk *disk)
if (WARN_ON(!q))
return;
+ if (!(disk->flags & GENHD_FL_HIDDEN)) {
+ sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
+ /*
+ * Unregister bdi before releasing device numbers (as they can
+ * get reused and we'd get clashes in sysfs).
+ */
+ bdi_unregister(q->backing_dev_info);
+ }
+
mutex_lock(&q->sysfs_lock);
queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
mutex_unlock(&q->sysfs_lock);
wbt_exit(q);
-
if (q->mq_ops)
blk_mq_unregister_dev(disk_to_dev(disk), q);
diff --git a/block/genhd.c b/block/genhd.c
index 00620e01e043..4a71aea1a1ef 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);
@@ -718,19 +708,8 @@ void del_gendisk(struct gendisk *disk)
set_capacity(disk, 0);
disk->flags &= ~GENHD_FL_UP;
- if (!(disk->flags & GENHD_FL_HIDDEN))
- sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
- if (disk->queue) {
- /*
- * Unregister bdi before releasing device numbers (as they can
- * get reused and we'd get clashes in sysfs).
- */
- if (!(disk->flags & GENHD_FL_HIDDEN))
- bdi_unregister(disk->queue->backing_dev_info);
+ if (disk->queue)
blk_unregister_queue(disk);
- } else {
- WARN_ON(1);
- }
if (!(disk->flags & GENHD_FL_HIDDEN))
blk_unregister_region(disk_devt(disk), disk->minors);
--
2.15.0
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