On Tue, Aug 8, 2017 at 3:38 AM, David Jeffery <djeffery@xxxxxxxxxx> wrote: > 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. I remember I saw this issue too. > > 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); Could you share why the lock of 'q->sysfs_lock' is needed here? > > 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; > + I suggest to check 'e->registered' here, which should be more reasonable or straightforward. -- Ming Lei
