Messages in this thread | | | Subject | Re: [PATCH -next 02/11] block, bfq: apply news apis where root group is not expected | From | "yukuai (C)" <> | Date | Wed, 13 Apr 2022 19:11:23 +0800 |
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在 2022/04/13 18:59, Jan Kara 写道: > 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 >> Hi,
Thanks for spotting this. >>> expected. Prepare to count root group into 'num_groups_with_pending_reqs'. >>> >>> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >>> --- >>> 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?
This is not a problem in theory, however 'entity->service' should always be 0 for root_group. Thus I think there is no need to do this.
>> >>> 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.
Yes, currently for_each_entity() and for_each_entity_not_root() are the same, they will stop before root_group.
With patch 5, for_each_entity_not_root() will stay the same, while for_each_entity() will access root_group's entity in addition. And because bfq_entity_service_tree() will access 'entity->sched_data', thus I change to the new api here to avoid null-ptr-deref after patch 5.
Same reasons for below changes.
Thanks, Kuai
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