[PATCH v2 3/3] block: Protect less code with sysfs_lock in blk_{un,}register_queue()

Bart Van Assche
2018-01-17T19:48:10Z

The __blk_mq_register_dev(), blk_mq_unregister_dev(),
elv_register_queue() and elv_unregister_queue() calls need to be
protected with sysfs_lock but other code in these functions not.
Hence protect only this code with sysfs_lock. This patch fixes a
locking inversion issue in blk_unregister_queue() and also in an
error path of blk_register_queue(): it is not allowed to hold
sysfs_lock around the kobject_del(&q->kobj) call.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
---
block/blk-sysfs.c | 37 ++++++++++++++++++++++++++++---------
1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 4a6a40ffd78e..cbea895a5547 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -853,6 +853,10 @@ struct kobj_type blk_queue_ktype = {
.release = blk_release_queue,
};

+/**
+ * blk_register_queue - register a block layer queue with sysfs
+ * @disk: Disk of which the request queue should be registered with sysfs.
+ */
int blk_register_queue(struct gendisk *disk)
{
int ret;
@@ -909,11 +913,12 @@ int blk_register_queue(struct gendisk *disk)
if (q->request_fn || (q->mq_ops && q->elevator)) {
ret = elv_register_queue(q);
if (ret) {
+ mutex_unlock(&q->sysfs_lock);
kobject_uevent(&q->kobj, KOBJ_REMOVE);
kobject_del(&q->kobj);
blk_trace_remove_sysfs(dev);
kobject_put(&dev->kobj);
- goto unlock;
+ return ret;
}
}
ret = 0;
@@ -923,6 +928,13 @@ int blk_register_queue(struct gendisk *disk)
}
EXPORT_SYMBOL_GPL(blk_register_queue);

+/**
+ * blk_unregister_queue - counterpart of blk_register_queue()
+ * @disk: Disk of which the request queue should be unregistered from sysfs.
+ *
+ * Note: the caller is responsible for guaranteeing that this function is called
+ * after blk_register_queue() has finished.
+ */
void blk_unregister_queue(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
@@ -935,8 +947,9 @@ void blk_unregister_queue(struct gendisk *disk)
return;

/*
- * Protect against the 'queue' kobj being accessed
- * while/after it is removed.
+ * Since sysfs_remove_dir() prevents adding new directory entries
+ * before removal of existing entries starts, protect against
+ * concurrent elv_iosched_store() calls.
*/
mutex_lock(&q->sysfs_lock);

@@ -944,18 +957,24 @@ void blk_unregister_queue(struct gendisk *disk)
queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
spin_unlock_irq(q->queue_lock);

- wbt_exit(q);
-
+ /*
+ * Remove the sysfs attributes before unregistering the queue data
+ * structures that can be modified through sysfs.
+ */
if (q->mq_ops)
blk_mq_unregister_dev(disk_to_dev(disk), q);
-
- if (q->request_fn || (q->mq_ops && q->elevator))
- elv_unregister_queue(q);
+ mutex_unlock(&q->sysfs_lock);

kobject_uevent(&q->kobj, KOBJ_REMOVE);
kobject_del(&q->kobj);
blk_trace_remove_sysfs(disk_to_dev(disk));
- kobject_put(&disk_to_dev(disk)->kobj);

+ wbt_exit(q);
+
+ mutex_lock(&q->sysfs_lock);
+ if (q->request_fn || (q->mq_ops && q->elevator))
+ elv_unregister_queue(q);
mutex_unlock(&q->sysfs_lock);
+
+ kobject_put(&disk_to_dev(disk)->kobj);
}
--
2.15.1