sch_htb: Fix inconsistency when leaf qdisc creation fails

In HTB offload mode, qdiscs of leaf classes are grafted to netdev
queues. sch_htb expects the dev_queue field of these qdiscs to point to
the corresponding queues. However, qdisc creation may fail, and in that
case noop_qdisc is used instead. Its dev_queue doesn't point to the
right queue, so sch_htb can lose track of used netdev queues, which will
cause internal inconsistencies.

This commit fixes this bug by keeping track of the netdev queue inside
struct htb_class. All reads of cl->leaf.q->dev_queue are replaced by the
new field, the two values are synced on writes, and WARNs are added to
assert equality of the two values.

The driver API has changed: when TC_HTB_LEAF_DEL needs to move a queue,
the driver used to pass the old and new queue IDs to sch_htb. Now that
there is a new field (offload_queue) in struct htb_class that needs to
be updated on this operation, the driver will pass the old class ID to
sch_htb instead (it already knows the new class ID).

Fixes: d03b195b5aa0 ("sch_htb: Hierarchical QoS hardware offload")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/20210826115425.1744053-1-maximmi@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index 8fb47fc61097..83a6d0792180 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -816,10 +816,9 @@ enum tc_htb_command {
 struct tc_htb_qopt_offload {
 	struct netlink_ext_ack *extack;
 	enum tc_htb_command command;
-	u16 classid;
 	u32 parent_classid;
+	u16 classid;
 	u16 qid;
-	u16 moved_qid;
 	u64 rate;
 	u64 ceil;
 };