Seeing lock order reversal

Alex Goncharov writes:

>  I am trying to source-upgrade one of my 7.0 systems to 8.0-CURRENT.

	I updated on Friday.


>  The very first 8.0 build (this morning) gave me the kernel that didn't
>  boot.  Built it again, finishing about 15 minutes ago.  This one
>  booted all right but I see this in `/var/log/messages':
>  
>  ================================================================================
>  WARNING: WITNESS option enabled, expect reduced performance.
>  lock order reversal:
>  1st 0xc4093e28 devfs (devfs) _at_ /mnt/wdx/freebsd/8.0/usr/src/sys/kern/vfs_subr.c:2064
>  2nd 0xc4172b54 devfsmount (devfsmount) _at_ /mnt/wdx/freebsd/8.0/usr/src/sys/fs/devfs/devfs_vnops.c:201
>  KDB: stack backtrace:
>  db_trace_self_wrapper(c0af5d71,e2888bbc,c07a70de,c0af8353,c4172b54,...) at db_trace_self_wrapper+0x26
>  kdb_backtrace(c0af8353,c4172b54,c0ae90df,c0ae90df,c0ae9120,...) at kdb_backtrace+0x29
>  witness_checkorder(c4172b54,9,c0ae9120,c9,c7,...) at witness_checkorder+0x6de
>  _sx_xlock(c4172b54,0,c0ae9120,c9,c4172b54,...) at _sx_xlock+0x7d
>  devfs_allocv(c415db80,c4174000,e2888c28,c3e1ecc0,c0afe288,...) at devfs_allocv+0x144
>  devfs_root(c4174000,2,c0c67378,c3e1ecc0,ca,...) at devfs_root+0x51
>  set_rootvnode(c0c67360,0,c0afe288,5f4,c07e4aa0,...) at set_rootvnode+0x2b
>  vfs_mountroot(c0c15270,4,c0aed8e7,264,0,...) at vfs_mountroot+0x356
>  start_init(0,e2888d38,c0aef370,30c,c3e1ccd0,...) at start_init+0x65
>  fork_exit(c0737740,0,e2888d38) at fork_exit+0xb8
>  fork_trampoline() at fork_trampoline+0x8
>  --- trap 0, eip = 0, esp = 0xe2888d70, ebp = 0 ---
>  Trying to mount root from ufs:/dev/ad4s1a
>  lock order reversal:
>  1st 0xc40939e8 ufs (ufs) _at_ /mnt/wdx/freebsd/8.0/usr/src/sys/kern/vfs_subr.c:2064
>  2nd 0xc4174000 vfslock (vfslock) _at_ /mnt/wdx/freebsd/8.0/usr/src/sys/kern/vfs_subr.c:364
>  KDB: stack backtrace:
>  db_trace_self_wrapper(c0af5d71,e28889d8,c07a70de,c0af8353,c4174000,...) at db_trace_self_wrapper+0x26
>  kdb_backtrace(c0af8353,c4174000,c0afe39a,c0afe39a,c0afe937,...) at kdb_backtrace+0x29
>  witness_checkorder(c4174000,1,c0afe937,16c,e2888a18,...) at witness_checkorder+0x6de
>  _lockmgr_args(c4174000,20001,c4174030,0,ffffffff,...) at _lockmgr_args+0x1d5
>  vfs_busy(c4174000,0,0,c3e1ecc0,e2888b58,...) at vfs_busy+0x1b0
>  lookup(e2888b44,c0afe022,c6,bf,c3dee22c,...) at lookup+0x7bf
>  namei(e2888b44,c4174030,1c1,c0afe288,e2888b54,...) at namei+0x34b
>  kern_unlink(c3e1ecc0,c0afe6d9,1,62f,0,...) at kern_unlink+0x40
>  vfs_mountroot_try(c0afe893,c0aec557,c0ae4ade,1,c07e4aa0,...) at vfs_mountroot_try+0x470
>  vfs_mountroot(c0c15270,4,c0aed8e7,264,0,...) at vfs_mountroot+0x418
>  start_init(0,e2888d38,c0aef370,30c,c3e1ccd0,...) at start_init+0x65
>  fork_exit(c0737740,0,e2888d38) at fork_exit+0xb8
>  fork_trampoline() at fork_trampoline+0x8
>  --- trap 0, eip = 0, esp = 0xe2888d70, ebp = 0 ---
>  lock order reversal:
>  1st 0xc3e22044 user map (user map) _at_ /mnt/wdx/freebsd/8.0/usr/src/sys/vm/vm_map.c:3111
>  2nd 0xc40937c8 ufs (ufs) _at_ /mnt/wdx/freebsd/8.0/usr/src/sys/kern/vfs_subr.c:2064
>  KDB: stack backtrace:
>  db_trace_self_wrapper(c0af5d71,e28889c4,c07a70de,c0af8353,c40937c8,...) at db_trace_self_wrapper+0x26
>  kdb_backtrace(c0af8353,c40937c8,c0aece96,c0aece96,c0afe937,...) at kdb_backtrace+0x29
>  witness_checkorder(c40937c8,1,c0afe937,810,e28889e8,...) at witness_checkorder+0x6de
>  _lockmgr_args(c40937c8,30041,c40937f8,0,ffffffff,...) at _lockmgr_args+0x1d5
>  ffs_lock(e2888a78,c075fc3d,c0c20554,30041,c4093770,...) at ffs_lock+0xa3
>  VOP_LOCK1_APV(c0bcbec0,e2888a78,c0aec555,3,c40937f8,...) at VOP_LOCK1_APV+0xa5
>  _vn_lock(c4093770,30041,c0afe937,810,0,...) at _vn_lock+0xf7
>  vget(c4093770,30041,c3e1ecc0,4a9,c1460600,...) at vget+0x10b
>  vnode_pager_lock(c1460480,0,c0b157d5,127,e2888be8,...) at vnode_pager_lock+0x1ad
>  vm_fault(c3e22000,80cf000,2,8,80cf340,...) at vm_fault+0x1df
>  trap_pfault(5,0,c0b23bd2,2c4,c3e1ccd0,...) at trap_pfault+0x118
>  trap(e2888d38) at trap+0x259
>  calltrap() at calltrap+0x6
>  --- trap 0xc, eip = 0x80480e5, esp = 0xbfbfeef0, ebp = 0xbfbfef10 ---

	I'm gettig both of these as well.  It doesn't stop the system
from booting, or _seem_ to affect operation ... but it would be nice
if they would go away.



				Robert Huff