[Patch net 03/12] sch_hfsc: make hfsc_qlen_notify() idempotent

Cong Wang
2025-03-20T23:25:51Z

hfsc_qlen_notify() is not idempotent either and not friendly
to its callers, like fq_codel_dequeue(). Let's make it idempotent
to ease qdisc_tree_reduce_backlog() callers' life:

1. update_vf() decreases cl->cl_nactive, so we can check whether it is
non-zero before calling it.

2. eltree_remove() always removes RB node cl->el_node, but we can use
RB_EMPTY_NODE() + RB_CLEAR_NODE() to make it safe.

Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
net/sched/sch_hfsc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index c287bf8423b4..ce5045eea065 100644
--- a/net/sched/sch_hfsc.c
+++ b/net/sched/sch_hfsc.c
@@ -203,7 +203,10 @@ eltree_insert(struct hfsc_class *cl)
static inline void
eltree_remove(struct hfsc_class *cl)
{
- rb_erase(&cl->el_node, &cl->sched->eligible);
+ if (!RB_EMPTY_NODE(&cl->el_node)) {
+ rb_erase(&cl->el_node, &cl->sched->eligible);
+ RB_CLEAR_NODE(&cl->el_node);
+ }
}

static inline void
@@ -1220,7 +1223,8 @@ hfsc_qlen_notify(struct Qdisc *sch, unsigned long arg)
/* vttree is now handled in update_vf() so that update_vf(cl, 0, 0)
* needs to be called explicitly to remove a class from vttree.
*/
- update_vf(cl, 0, 0);
+ if (cl->cl_nactive)
+ update_vf(cl, 0, 0);
if (cl->cl_flags & HFSC_RSC)
eltree_remove(cl);
}
--
2.34.1