linux-kernel - Re: [Regression Bug] Re: [PATCH net v3 2/2] ppp: fix race conditions in ppp_fill_forward

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Message-ID: <CALW65jY4MBCwt=XdzObMQBzN5FgtWjd=XrMBGDHQi9uuknK-og@mail.gmail.com>
Date: Fri, 29 Aug 2025 23:30:57 +0800
From: Qingfang Deng <dqfext@...il.com>
To: cam enih <nanericwang@...il.com>
Cc: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, kuniyu@...gle.com, linux-kernel@...r.kernel.org, 
	linux-ppp@...r.kernel.org, nbd@....name, netdev@...r.kernel.org, 
	pabeni@...hat.com, pablo@...filter.org
Subject: Re: [Regression Bug] Re: [PATCH net v3 2/2] ppp: fix race conditions
 in ppp_fill_forward_path

Hi Eric,

On Fri, Aug 29, 2025 at 9:05 PM cam enih <nanericwang@...il.com> wrote:
>
> Hi all,
> Having upgraded from 6.12.43 to 6.12.44, my kernel crashed at early boot. The root cause is most likely related to the commit 94731cc551e29511d85aa8dec61a6c071b1f2430 (Fixes: f6efc675c9dd ("net: ppp: resolve forwarding path for bridge pppoe devices")). Please confirm, thanks.

Does this happen only if you set up a PPPoE connection?

>
> -Eric
>
> ```
> Aug 29 20:36:16 localhost kernel: NET: Registered PF_PPPOX protocol family
> Aug 29 20:36:17 localhost systemd-networkd[266]: Failed to parse hostname, ignoring: Invalid argument
> Aug 29 20:36:17 localhost systemd-networkd[266]: br0: DHCPv4 server: DISCOVER (0xebeec00c)
> Aug 29 20:36:17 localhost kernel: BUG: kernel NULL pointer dereference, address: 0000000000000058
> Aug 29 20:36:17 localhost kernel: #PF: supervisor read access in kernel mode
> Aug 29 20:36:17 localhost kernel: #PF: error_code(0x0000) - not-present page
> Aug 29 20:36:17 localhost kernel: PGD 0 P4D 0
> Aug 29 20:36:17 localhost kernel: Oops: Oops: 0000 [#1] PREEMPT_RT SMP
> Aug 29 20:36:17 localhost kernel: CPU: 1 UID: 981 PID: 266 Comm: systemd-network Not tainted 6.12.44-xanmod1-1-lts #1

Looks like it's a downstream fork:
https://gitlab.com/xanmod/linux/-/releases/6.12.44-xanmod1
Have you reported to them too?

> Aug 29 20:36:17 localhost kernel: Hardware name: Default string Default string/Default string, BIOS 5.19 03/30/2021
> Aug 29 20:36:17 localhost kernel: RIP: 0010:0xffffffffb32b2f6c
> Aug 29 20:36:17 localhost kernel: Code: 85 8e 01 00 00 48 8b 44 24 08 48 8b 40 30 65 48 03 05 48 26 d6 4c e9 f0 fd ff ff e8 5e 9c c1 ff e9 ca fc ff ff 49 8b 44 24 18 <48> 8b 40 58 48 3d 00 e3 65 b3 0f 84 0f 01 00 00 48 89 c2 48 8d 78
> Aug 29 20:36:17 localhost kernel: RSP: 0018:ffff9bd080c778d8 EFLAGS: 00010246
> Aug 29 20:36:17 localhost kernel: RAX: 0000000000000000 RBX: ffff9bd080c77a00 RCX: 0000000000000001
> Aug 29 20:36:17 localhost kernel: RDX: 0000000000000000 RSI: 000000000002a424 RDI: ffffffffb38b6040
> Aug 29 20:36:17 localhost kernel: RBP: ffff999345ad1000 R08: 0000000000000003 R09: 0000000000000000
> Aug 29 20:36:17 localhost kernel: R10: ffff999342eb7900 R11: 0000000000000000 R12: ffff9bd080c77948
> Aug 29 20:36:17 localhost kernel: R13: 0000000000000008 R14: 0000000000000000 R15: 0000000090000000
> Aug 29 20:36:17 localhost kernel: FS: 00007fc0bab148c0(0000) GS:ffff9994b7d00000(0000) knlGS:0000000000000000
> Aug 29 20:36:17 localhost kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> Aug 29 20:36:17 localhost kernel: CR2: 0000000000000058 CR3: 000000010b438006 CR4: 0000000000b70ef0
> Aug 29 20:36:17 localhost kernel: Call Trace:
> Aug 29 20:36:17 localhost kernel: <TASK>
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb321d725
> Aug 29 20:36:17 localhost kernel: 0xffffffffb32b4197
> Aug 29 20:36:17 localhost kernel: 0xffffffffb32f5d6c
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb32b8c40
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb3212da5
> Aug 29 20:36:17 localhost kernel: 0xffffffffb3212da5
> Aug 29 20:36:17 localhost kernel: 0xffffffffb32131ea
> Aug 29 20:36:17 localhost kernel: 0xffffffffb32152ea
> Aug 29 20:36:17 localhost kernel: 0xffffffffb3364479
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb3364485
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb3215617
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb2f2cd31
> Aug 29 20:36:17 localhost kernel: ? 0xffffffffb33684f7
> Aug 29 20:36:17 localhost kernel: 0xffffffffb34000b0

Do they have a debug kernel image with KALLSYMS, so I won't be looking
at some random hex?

Thanks
- Qingfang