There is a race between changing I/O elevator and request_queue removal which can trigger the warning in kobject_add_internal. A program can use sysfs to request a change of elevator at the same time another task is unregistering the request_queue the elevator would be attached to. The elevator's kobject will then attempt to be connected to the request_queue in the object tree when the request_queue has just been removed from sysfs. This triggers the warning in kobject_add_internal as the request_queue no longer has a sysfs directory: kobject_add_internal failed for iosched (error: -2 parent: queue) ------------[ cut here ]------------ WARNING: CPU: 3 PID: 14075 at lib/kobject.c:244 kobject_add_internal+0x103/0x2d0 To fix this warning, we can check the QUEUE_FLAG_REGISTERED flag when changing the elevator and use the request_queue's sysfs_lock to serialize between clearing the flag and the elevator testing the flag. Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx> --- block/blk-sysfs.c | 2 ++ block/elevator.c | 4 ++++ 2 files changed, 6 insertions(+) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 27aceab..b8362c0 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -931,7 +931,9 @@ void blk_unregister_queue(struct gendisk *disk) if (WARN_ON(!q)) return; + mutex_lock(&q->sysfs_lock); queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q); + mutex_unlock(&q->sysfs_lock); wbt_exit(q); diff --git a/block/elevator.c b/block/elevator.c index 4bb2f0c..51da592 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -1055,6 +1055,10 @@ static int __elevator_change(struct request_queue *q, const char *name) char elevator_name[ELV_NAME_MAX]; struct elevator_type *e; + /* Make sure queue is not in the middle of being removed */ + if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) + return -ENOENT; + /* * Special case for mq, turn off scheduling */
