From: Paolo Valente <paolo.valente@xxxxxxxxxx> commit 4d38a87fbb77fb9ff2ff4e914162a8ae6453eff5 upstream. In bfq_pd_offline(), the function bfq_flush_idle_tree() is invoked to flush the rb tree that contains all idle entities belonging to the pd (cgroup) being destroyed. In particular, bfq_flush_idle_tree() is invoked before bfq_reparent_active_queues(). Yet the latter may happen to add some entities to the idle tree. It happens if, in some of the calls to bfq_bfqq_move() performed by bfq_reparent_active_queues(), the queue to move is empty and gets expired. This commit simply reverses the invocation order between bfq_flush_idle_tree() and bfq_reparent_active_queues(). Tested-by: cki-project@xxxxxxxxxx Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/bfq-cgroup.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) --- a/block/bfq-cgroup.c +++ b/block/bfq-cgroup.c @@ -877,13 +877,6 @@ static void bfq_pd_offline(struct blkg_p st = bfqg->sched_data.service_tree + i; /* - * The idle tree may still contain bfq_queues belonging - * to exited task because they never migrated to a different - * cgroup from the one being destroyed now. - */ - bfq_flush_idle_tree(st); - - /* * It may happen that some queues are still active * (busy) upon group destruction (if the corresponding * processes have been forced to terminate). We move @@ -896,6 +889,19 @@ static void bfq_pd_offline(struct blkg_p * scheduler has taken no reference. */ bfq_reparent_active_queues(bfqd, bfqg, st, i); + + /* + * The idle tree may still contain bfq_queues + * belonging to exited task because they never + * migrated to a different cgroup from the one being + * destroyed now. In addition, even + * bfq_reparent_active_queues() may happen to add some + * entities to the idle tree. It happens if, in some + * of the calls to bfq_bfqq_move() performed by + * bfq_reparent_active_queues(), the queue to move is + * empty and gets expired. + */ + bfq_flush_idle_tree(st); } __bfq_deactivate_entity(entity, false);
