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 <snitzer@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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
@@ -929,13 +929,18 @@
if (WARN_ON(!q))
return;
+ /*
+ * Protect against the 'queue' kobj being accessed
+ * while/after it is removed.
+ */
mutex_lock(&q->sysfs_lock);
- queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
- mutex_unlock(&q->sysfs_lock);
+
+ 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 @@
kobject_del(&q->kobj);
blk_trace_remove_sysfs(disk_to_dev(disk));
kobject_put(&disk_to_dev(disk)->kobj);
+
+ mutex_unlock(&q->sysfs_lock);
}