Commit ce8fe975 authored by Cong Wang's avatar Cong Wang Committed by Jakub Kicinski
Browse files

net_sched: skbprio: Remove overly strict queue assertions 



In the current implementation, skbprio enqueue/dequeue contains an assertion
that fails under certain conditions when SKBPRIO is used as a child qdisc under
TBF with specific parameters. The failure occurs because TBF sometimes peeks at
packets in the child qdisc without actually dequeuing them when tokens are
unavailable.

This peek operation creates a discrepancy between the parent and child qdisc
queue length counters. When TBF later receives a high-priority packet,
SKBPRIO's queue length may show a different value than what's reflected in its
internal priority queue tracking, triggering the assertion.

The fix removes this overly strict assertions in SKBPRIO, they are not
necessary at all.

Reported-by: default avatar <syzbot+a3422a19b05ea96bee18@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=a3422a19b05ea96bee18


Fixes: aea5f654 ("net/sched: add skbprio scheduler")
Cc: Nishanth Devarajan <ndev2021@gmail.com>
Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Acked-by: default avatarPaolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/20250329222536.696204-2-xiyou.wangcong@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 078aabd5

net/sched/sch_skbprio.c

+0 −3
Original line number Diff line number Diff line
@@ -123,8 +123,6 @@ static int skbprio_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
	/* Check to update highest and lowest priorities. */

	if (skb_queue_empty(lp_qdisc)) {

		if (q->lowest_prio == q->highest_prio) {

			/* The incoming packet is the only packet in queue. */

			BUG_ON(sch->q.qlen != 1);

			q->lowest_prio = prio;

			q->highest_prio = prio;

		} else {
@@ -156,7 +154,6 @@ static struct sk_buff *skbprio_dequeue(struct Qdisc *sch) 
	/* Update highest priority field. */

	if (skb_queue_empty(hpq)) {

		if (q->lowest_prio == q->highest_prio) {

			BUG_ON(sch->q.qlen);

			q->highest_prio = 0;

			q->lowest_prio = SKBPRIO_MAX_PRIORITY - 1;

		} else {