Commit b410aff2 authored Feb 14, 2017 by Tahsin Erdogan Committed by Jens Axboe Feb 15, 2017

block: do not allow updates through sysfs until registration completes



When a new disk shows up, sysfs queue directory is created before elevator
is registered. This allows a user to attempt a scheduler switch even though
the initial registration hasn't completed yet.

In one scenario, blk_register_queue() calls elv_register_queue() and
right before cfq_registered_queue() is called, another process executes
elevator_switch() and replaces q->elevator with deadline scheduler. When
cfq_registered_queue() executes it interprets e->elevator_data as struct
cfq_data even though it is actually struct deadline_data.

Grab q->sysfs_lock in blk_register_queue() to synchronize with sysfs
callers.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 3d492c2e

block/blk-sysfs.c

+12 −7

Original line number	Diff line number	Diff line
		@@ -902,17 +902,20 @@ int blk_register_queue(struct gendisk *disk)
		if (ret)
		return ret;

		if (q->mq_ops)
		blk_mq_register_dev(dev, q);

		/* Prevent changes through sysfs until registration is completed. */
		mutex_lock(&q->sysfs_lock);

		ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue");
		if (ret < 0) {
		blk_trace_remove_sysfs(dev);
		return ret;
		goto unlock;
		}

		kobject_uevent(&q->kobj, KOBJ_ADD);

		if (q->mq_ops)
		blk_mq_register_dev(dev, q);

		blk_wb_init(q);

		if (q->request_fn \|\| (q->mq_ops && q->elevator)) {
		@@ -922,11 +925,13 @@ int blk_register_queue(struct gendisk *disk)
		kobject_del(&q->kobj);
		blk_trace_remove_sysfs(dev);
		kobject_put(&dev->kobj);
		return ret;
		goto unlock;
		}
		}

		return 0;
		ret = 0;
		unlock:
		mutex_unlock(&q->sysfs_lock);
		return ret;
		}

		void blk_unregister_queue(struct gendisk *disk)