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@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?
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
