Re: kern/38291: panic: LOCKDEBUG, _kernel_unlock: assertion failed: nlocks <= 0, unmounting MFS /tmp

[Andrew Doran <ad%netbsd.org@localhost>]

The following reply was made to PR kern/38291; it has been noted by GNATS.

From: Andrew Doran <ad%netbsd.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/38291: panic: LOCKDEBUG, _kernel_unlock: assertion failed: 
nlocks <= 0, unmounting MFS /tmp
Date: Tue, 25 Mar 2008 14:29:41 +0000

 > panic: LOCKDEBUG
 > Stopped in pid 156.1 (mount_mfs) at     netbsd:breakpoint+0x4:  popl    %ebp
 > db{1}> trace
 > breakpoint(cdadba58,0,cdadba8c,c0582fb7,c0a2932f) at netbsd:breakpoint+0x4
 > cpu_Debugger(c0a2932f,cdadba98,c36b1800,c0583e67,0) at 
 > netbsd:cpu_Debugger+0xb
 > panic(c0a284f0,c0583e06,c0a229ee,c0a22a1a,1f) at netbsd:panic+0x164
 > lockdebug_abort1(c0d54c40,c0d5e6a0,c0a229ee,c0a22a1a,1) at 
 > netbsd:lockdebug_abort1+0x8d
 > lockdebug_abort(c0d51a40,c0c92eb8,c0a229ee,c0a22a1a,cdd5552c) at 
 > netbsd:lockdebug_abort+0x4b
 > _kernel_unlock(1,cdaec460,0,c05c9e56,cdc5f3c4) at netbsd:_kernel_unlock+0x7d
 > VFS_START(cdc5f3c4,0,3,cdadbcb0,0) at netbsd:VFS_START+0x6f
 > mount_domount(cdaec460,cdadbc7c,c0c902a0,bfbfffa2,58) at 
 > netbsd:mount_domount+0x3f5
 > do_sys_mount(cdaec460,c0c902a0,8076522,bfbfffa2,58) at 
 > netbsd:do_sys_mount+0x254
 > compat_40_sys_mount(cdaec460,cdadbd04,cdadbcfc,cdadbd30,c064b7db) at 
 > netbsd:compat_40_sys_mount+0x59
 > syscall(cdadbd48,b3,ab,bfbf001f,1f) at netbsd:syscall+0x17b
 > db{1}> x/I 0x00000000c066dc69
 > netbsd:syscall+0x193:   movl    0xfffffff0(%ebp),%eax
 > db{1}> x/I 0x00000000c0526d14
 > netbsd:main+0x2f:       call    netbsd:uvm_init
 > db{1}> 
 
 At a guess, the mountpoint is being destroyed. As mount_dounmount() returns
 it reads garbage from mp->mnt_iflag and so tries to drop kernel_lock. This
 may not have happened before because of a different set of garbage in memory
 at the time.
 
 Andrew