On Wed 13-04-22 11:50:44, Jan Kara wrote: > On Sat 05-03-22 17:11:56, Yu Kuai wrote: > > 'entity->sched_data' is set to parent group's sched_data, thus it's NULL > > for root group. And for_each_entity() is used widely to access > > 'entity->sched_data', thus aplly news apis if root group is not > ^^ apply > > > expected. Prepare to count root group into 'num_groups_with_pending_reqs'. > > > > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> > > --- > > block/bfq-iosched.c | 2 +- > > block/bfq-iosched.h | 22 ++++++++-------------- > > block/bfq-wf2q.c | 10 +++++----- > > 3 files changed, 14 insertions(+), 20 deletions(-) > > > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > > index 69ddf6b0f01d..3bc7a7686aad 100644 > > --- a/block/bfq-iosched.c > > +++ b/block/bfq-iosched.c > > @@ -4393,7 +4393,7 @@ void bfq_bfqq_expire(struct bfq_data *bfqd, > > * service with the same budget. > > */ > > entity = entity->parent; > > - for_each_entity(entity) > > + for_each_entity_not_root(entity) > > entity->service = 0; > > } > > So why is it a problem to clear the service for root cgroup here? > > > diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c > > index f8eb340381cf..c4cb935a615a 100644 > > --- a/block/bfq-wf2q.c > > +++ b/block/bfq-wf2q.c > > @@ -815,7 +815,7 @@ void bfq_bfqq_served(struct bfq_queue *bfqq, int served) > > bfqq->service_from_wr += served; > > > > bfqq->service_from_backlogged += served; > > - for_each_entity(entity) { > > + for_each_entity_not_root(entity) { > > st = bfq_entity_service_tree(entity); > > Hum, right so how come this was not crashing? Because entity->sched_data is > indeed NULL for bfqd->root_group->entity and so bfq_entity_service_tree() > returned some bogus pointer? Similarly for the cases you are changing > below? Oh, I see now. Because for_each_entity() currently does not iterate through root cgroup because it has root_group->my_entity set to NULL and thus as a result immediate children of root_group will have their parent set to NULL as well. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR