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

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Message-ID: <6fa68b02-cf82-aeca-56e6-e3b8565b22f4@applied-asynchrony.com>
Date: Mon, 21 Apr 2025 13:50:52 +0200
From: Holger Hoffstätte <holger@...lied-asynchrony.com>
To: "Alan J. Wylie" <alan@...ie.me.uk>, 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 2025-04-21 11:40, Alan J. Wylie wrote:
> #regzbot introduced: 6.14.2..6.14.3
> 
> Since 6.14.3 I have been seeing random panics, all in htb_dequeue.
> 6.14.2 was fine.

6.14.3 contains:
"codel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()" aka
https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/net/sched?h=linux-6.14.y&id=a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31

Is your HTB backed by fq_codel by any chance? If so, try either
reverting the above or adding:
"sch_htb: make htb_qlen_notify() idempotent" aka
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5ba8b837b522d7051ef81bacf3d95383ff8edce5

which was successfully not added to 6.14.3, along with the rest of the series:
https://lore.kernel.org/all/20250403211033.166059-2-xiyou.wangcong@gmail.com/

Hope this helps. I am running fq_codel without issue but not behind htb.

cheers
Holger