path: root/block/blk-sysfs.c
diff options
authorMike Snitzer <>2018-01-11 14:11:01 -0500
committerJens Axboe <>2018-01-15 08:41:38 -0700
commit667257e8b2988c0183ba23e2bcd6900e87961606 (patch)
treeae0ec92e1fe69f71788169e07789096357f0c4ba /block/blk-sysfs.c
parentbc8d062c36e3525e81ea8237ff0ab3264c2317b6 (diff)
block: properly protect the 'queue' kobj in blk_unregister_queue
The original commit e9a823fb34a8b (block: fix warning when I/O elevator is changed as request_queue is being removed) is pretty conflated. "conflated" because the resource being protected by q->sysfs_lock isn't the queue_flags (it is the 'queue' kobj). q->sysfs_lock serializes __elevator_change() (via elv_iosched_store) from racing with blk_unregister_queue(): 1) By holding q->sysfs_lock first, __elevator_change() can complete before a racing blk_unregister_queue(). 2) Conversely, __elevator_change() is testing for QUEUE_FLAG_REGISTERED in case elv_iosched_store() loses the race with blk_unregister_queue(), it needs a way to know the 'queue' kobj isn't there. Expand the scope of blk_unregister_queue()'s q->sysfs_lock use so it is held until after the 'queue' kobj is removed. To do so blk_mq_unregister_dev() must not also take q->sysfs_lock. So rename __blk_mq_unregister_dev() to blk_mq_unregister_dev(). Also, blk_unregister_queue() should use q->queue_lock to protect against any concurrent writes to q->queue_flags -- even though chances are the queue is being cleaned up so no concurrent writes are likely. Fixes: e9a823fb34a8b ("block: fix warning when I/O elevator is changed as request_queue is being removed") Signed-off-by: Mike Snitzer <> Reviewed-by: Ming Lei <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block/blk-sysfs.c')
1 files changed, 10 insertions, 3 deletions
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 870484e..9272452 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -929,12 +929,17 @@ void blk_unregister_queue(struct gendisk *disk)
if (WARN_ON(!q))
+ /*
+ * Protect against the 'queue' kobj being accessed
+ * while/after it is removed.
+ */
- queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
- mutex_unlock(&q->sysfs_lock);
- wbt_exit(q);
+ spin_lock_irq(q->queue_lock);
+ queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
+ spin_unlock_irq(q->queue_lock);
+ wbt_exit(q);
if (q->mq_ops)
blk_mq_unregister_dev(disk_to_dev(disk), q);
@@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk)
+ mutex_unlock(&q->sysfs_lock);