NetBSD Problem Report #59963

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Date: Thu,  5 Feb 2026 10:56:17 +0000 (UTC)
From: roy@marples.name
Reply-To: roy@marples.name
To: gnats-bugs@NetBSD.org
Subject: Lock Order Reversal issue with PPP
X-Send-Pr-Version: www-1.0
X-From4GNATS: "roy@marples.name via gnats" <gnats-admin@NetBSD.org>

>Number:         59963
>Category:       kern
>Synopsis:       Lock Order Reversal issue with PPP
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Feb 05 11:00:00 +0000 2026
>Last-Modified:  Wed Mar 04 20:25:01 +0000 2026
>Originator:     Roy Marples
>Release:        11.99.5
>Organization:
>Environment:
NetBSD cube 11.99.5 NetBSD 11.99.5 (GENERIC) #1: Sun Feb  1 19:02:06 GMT 2026  roy@cube:/home/roy/src/obj/sys/arch/amd64/compile/GENERIC amd64
>Description:
PPPoE traffic causes a missed heartbeat panic.
>How-To-Repeat:
Setup your NetBSD-11 host OS as a PPPoE server.
Setup your NetBSD-11 guest OS as a PPPoE client.

After starting the guest either the host or guest will panic with a hearbeat error.

As the host uses a USB keyboard it's challenging to get anything meaningful out of it.
The guest can be interrogated via VNC to get the following screenshot showing the stuck process.
https://mollari.netbsd.org/~roy/intr.png
>Fix:

>Audit-Trail:
From: Roy Marples <roy@marples.name>
To: "gnats-bugs" <gnats-bugs@netbsd.org>
Cc: 
Subject: Re: kern/59963: Lock Order Reversal issue with PPP
Date: Sun, 08 Feb 2026 15:36:55 +0000

 More info

 https://mollari.netbsd.org/~roy/intr_softnet_lock.png
 https://mollari.netbsd.org/~roy/intr_showlock.png


From: Roy Marples <roy@marples.name>
To: "gnats-bugs" <gnats-bugs@netbsd.org>
Cc: "kern-bug-people" <kern-bug-people@netbsd.org>,
	"gnats-admin" <gnats-admin@netbsd.org>,
	"netbsd-bugs" <netbsd-bugs@netbsd.org>
Subject: Re: kern/59963: Lock Order Reversal issue with PPP
Date: Sun, 08 Feb 2026 20:23:45 +0000

 Thanks to skrll@ and riastradh@ we have more screenshots:

 https://mollari.netbsd.org/~roy/pppoe_lock.png
 https://mollari.netbsd.org/~roy/intr_lock_bt.png


From: Roy Marples <roy@marples.name>
To: "gnats-bugs" <gnats-bugs@netbsd.org>
Cc: "kern-bug-people" <kern-bug-people@netbsd.org>,
	"gnats-admin" <gnats-admin@netbsd.org>,
	"netbsd-bugs" <netbsd-bugs@netbsd.org>
Subject: Re: kern/59963: Lock Order Reversal issue with PPP
Date: Sun, 08 Feb 2026 21:06:04 +0000

 Dropping the SPPP lock before each call to rt_ifmsg and aquiring it again fixes the issue.

 Patch here:
 https://mollari.netbsd.org/~roy/ppp_rt_ifmsg.diff

 Comments welcome.

From: "Roy Marples" <roy@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59963 CVS commit: src/sys/net
Date: Tue, 24 Feb 2026 16:02:05 +0000

 Module Name:	src
 Committed By:	roy
 Date:		Tue Feb 24 16:02:05 UTC 2026

 Modified Files:
 	src/sys/net: if_spppsubr.c

 Log Message:
 PPP: drop SPPP lock before calling rt_ifmsg

 rt_ifmsg will lock SPPP itself, so ensure it's unlocked before calling.
 Add a comment to explain why this should be safe.

 Thanks to @riastradh for review and commentary.

 Fixes PR kern/59963.


 To generate a diff of this commit:
 cvs rdiff -u -r1.273 -r1.274 src/sys/net/if_spppsubr.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Martin Husemann" <martin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59963 CVS commit: [netbsd-11] src/sys/net
Date: Wed, 4 Mar 2026 20:22:46 +0000

 Module Name:	src
 Committed By:	martin
 Date:		Wed Mar  4 20:22:46 UTC 2026

 Modified Files:
 	src/sys/net [netbsd-11]: if_spppsubr.c

 Log Message:
 Pull up following revision(s) (requested by roy in ticket #201):

 	sys/net/if_spppsubr.c: revision 1.274

 PPP: drop SPPP lock before calling rt_ifmsg
 rt_ifmsg will lock SPPP itself, so ensure it's unlocked before calling.

 Add a comment to explain why this should be safe.

 Thanks to @riastradh for review and commentary.
 Fixes PR kern/59963.


 To generate a diff of this commit:
 cvs rdiff -u -r1.271.2.1 -r1.271.2.2 src/sys/net/if_spppsubr.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

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