[Patch net 02/12] sch_drr: make drr_qlen_notify() idempotent

Cong Wang
2025-03-20T23:25:50Z

drr_qlen_notify() always deletes the DRR class from its active list
with list_del(), therefore, it is not idempotent and not friendly
to its callers, like fq_codel_dequeue().

Let's make it idempotent to ease qdisc_tree_reduce_backlog() callers'
life. Also change other list_del()'s to list_del_init() just to be
extra safe.

Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
net/sched/sch_drr.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
index c69b999fae17..e0a81d313aa7 100644
--- a/net/sched/sch_drr.c
+++ b/net/sched/sch_drr.c
@@ -105,6 +105,7 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
return -ENOBUFS;

gnet_stats_basic_sync_init(&cl->bstats);
+ INIT_LIST_HEAD(&cl->alist);
cl->common.classid = classid;
cl->quantum = quantum;
cl->qdisc = qdisc_create_dflt(sch->dev_queue,
@@ -229,7 +230,7 @@ static void drr_qlen_notify(struct Qdisc *csh, unsigned long arg)
{
struct drr_class *cl = (struct drr_class *)arg;

- list_del(&cl->alist);
+ list_del_init(&cl->alist);
}

static int drr_dump_class(struct Qdisc *sch, unsigned long arg,
@@ -390,7 +391,7 @@ static struct sk_buff *drr_dequeue(struct Qdisc *sch)
if (unlikely(skb == NULL))
goto out;
if (cl->qdisc->q.qlen == 0)
- list_del(&cl->alist);
+ list_del_init(&cl->alist);

bstats_update(&cl->bstats, skb);
qdisc_bstats_update(sch, skb);
@@ -431,7 +432,7 @@ static void drr_reset_qdisc(struct Qdisc *sch)
for (i = 0; i < q->clhash.hashsize; i++) {
hlist_for_each_entry(cl, &q->clhash.hash[i], common.hnode) {
if (cl->qdisc->q.qlen)
- list_del(&cl->alist);
+ list_del_init(&cl->alist);
qdisc_reset(cl->qdisc);
}
}
--
2.34.1