linux-kernel - Re: [REGRESSION] 6.14.3 panic - kernel NULL pointer dereference in htb

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Message-ID: <20250421210927.50d6a355@frodo.int.wylie.me.uk>
Date: Mon, 21 Apr 2025 21:09:27 +0100
From: "Alan J. Wylie" <alan@...ie.me.uk>
To: Holger Hoffstätte <holger@...lied-asynchrony.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, regressions@...ts.linux.dev, Cong
 Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Octavian Purdila
 <tavip@...gle.com>, Toke Høiland-Jørgensen
 <toke@...hat.com>, stable@...r.kernel.org
Subject: Re: [REGRESSION] 6.14.3 panic - kernel NULL pointer dereference in
 htb_dequeue

On Mon, 21 Apr 2025 21:47:44 +0200
Holger Hoffstätte <holger@...lied-asynchrony.com> wrote:

> > I'm afraid that didn't help. Same panic.  
> 
> Bummer :-(
> 
> Might be something else missing then - so for now the only other thing
> I'd suggest is to revert the removal of the qlen check in fq_codel.

Like this?

$ git diff  sch_fq_codel.c
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index 6c9029f71e88..4fdf317b82ec 100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -316,7 +316,7 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
        qdisc_bstats_update(sch, skb);
        flow->deficit -= qdisc_pkt_len(skb);

-       if (q->cstats.drop_count) {
+       if (q->cstats.drop_count && sch->q.qlen) {
                qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
                                          q->cstats.drop_len);
                q->cstats.drop_count = 0;
$ 

I'll be off to bed soon, but I'll leave it running overnight.

I might be able to do a quick report in the morning, but I'll
have to set off early to go digging down a cave all day tomorrow.

-- 
Alan J. Wylie     https://www.wylie.me.uk/     mailto:<alan@...ie.me.uk>

Dance like no-one's watching. / Encrypt like everyone is.
Security is inversely proportional to convenience