NetBSD Problem Report #52255

From paul@whooppee.com  Wed May 24 03:34:10 2017
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Message-Id: <20170524033408.15B8B16E68@speedy.whooppee.com>
Date: Wed, 24 May 2017 11:34:08 +0800 (+08)
From: paul@whooppee.com
Reply-To: paul@whooppee.com
To: gnats-bugs@NetBSD.org
Subject: if_tun panic in tun_clone_destroy()
X-Send-Pr-Version: 3.95

>Number:         52255
>Category:       kern
>Synopsis:       if_tun panic in tun_clone_destroy()
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 24 03:35:00 +0000 2017
>Closed-Date:    Wed May 24 06:54:09 +0000 2017
>Last-Modified:  Wed May 24 06:55:00 +0000 2017
>Originator:     Paul Goyette
>Release:        NetBSD 7.99.71
>Organization:
+------------------+--------------------------+----------------------------+
| Paul Goyette     | PGP Key fingerprint:     | E-mail addresses:          |
| (Retired)        | FA29 0E3B 35AF E8AE 6651 | paul at whooppee dot com   |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd dot org |
+------------------+--------------------------+----------------------------+
>Environment:


System: NetBSD speedy.whooppee.com 7.99.71 NetBSD 7.99.71 (SPEEDY 2017-05-11 00:01:07 UTC) #0: Thu May 11 04:22:38 UTC 2017 paul@speedy.whooppee.com:/build/netbsd-local/obj/amd64/sys/arch/amd64/compile/SPEEDY amd64
Architecture: x86_64
Machine: amd64
>Description:
When built with lockdebug, tun_clone_destroy() encounters a panic when
calling kmem_intr_free() to free the device's softc.  It seems that there
is still an active lock contained within the softc.

A little investigation shows that the lock must actually be inside the
'struct ifnet'; the only lock inside the tun-specific portion of the softc
is the tun_lock, which is already being kmutex_destroy()d before the call
to kmem_intr_free().  But I don't see anywhere where the actual kmutex is
contained inside 'struct ifnet' - just pointers to various lock things.


>How-To-Repeat:
1. Bring up a tunnel (I use openvpn for this)
2. Shut the system down, which should cause the tunnel to be destroyed

>Fix:
Not known.

XXX
Note that other cloning network devices might well have a similar bug!


>Release-Note:

>Audit-Trail:
From: Paul Goyette <paul@whooppee.com>
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: kern/52255: if_tun panic in tun_clone_destroy()
Date: Wed, 24 May 2017 11:37:38 +0800 (+08)

 >> How-To-Repeat:
 > 1. Bring up a tunnel (I use openvpn for this)
 > 2. Shut the system down, which should cause the tunnel to be destroyed

 Note an important step 0!

 0. Build and boot a kernel with 'options LOCKDEBUG' enabled

 :)

State-Changed-From-To: open->closed
State-Changed-By: pgoyette@NetBSD.org
State-Changed-When: Wed, 24 May 2017 06:54:09 +0000
State-Changed-Why:
Fix committed


From: "Paul Goyette" <pgoyette@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/52255 CVS commit: src/sys/net
Date: Wed, 24 May 2017 06:52:15 +0000

 Module Name:	src
 Committed By:	pgoyette
 Date:		Wed May 24 06:52:14 UTC 2017

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

 Log Message:
 Call cv_destroy() to deactivate the tun_cv before calling kmem_intr_free()
 to deallocate the containing memory chunk (the tunnel's softc).  Otherwise
 a LOCKDEBUG kernel will panic in tun_clone_destroy().

 Fixes PR kern/52255


 To generate a diff of this commit:
 cvs rdiff -u -r1.138 -r1.139 src/sys/net/if_tun.c

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

>Unformatted:

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