block: Document scheduler modification locking requirements

This patch does not change any functionality.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 8 insertions, 0 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 4f00b53cd5fd..e87e9b43aba0 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -869,6 +869,8 @@ int elv_register_queue(struct request_queue *q)
         struct elevator_queue *e = q->elevator;
         int error;
 
+        lockdep_assert_held(&q->sysfs_lock);
+
         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
         if (!error) {
                 struct elv_fs_entry *attr = e->type->elevator_attrs;
@@ -889,6 +891,8 @@ int elv_register_queue(struct request_queue *q)
 
 void elv_unregister_queue(struct request_queue *q)
 {
+        lockdep_assert_held(&q->sysfs_lock);
+
         if (q) {
                 struct elevator_queue *e = q->elevator;
 
@@ -965,6 +969,8 @@ static int elevator_switch_mq(struct request_queue *q,
 {
         int ret;
 
+        lockdep_assert_held(&q->sysfs_lock);
+
         blk_mq_freeze_queue(q);
         blk_mq_quiesce_queue(q);
 
@@ -1010,6 +1016,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
         bool old_registered = false;
         int err;
 
+        lockdep_assert_held(&q->sysfs_lock);
+
         if (q->mq_ops)
                 return elevator_switch_mq(q, new_e);