Re: Seeing lock order reversal

On 18/03/2008, Attilio Rao <attilio_at_freebsd.org> wrote:
> 2008/3/18, pluknet <pluknet_at_gmail.com>:
>  >
>  >  Thought taking that into account I could obtain a new one yesterday. I
>  >  didn't see this before.
>  >
>  >  Mar 17 03:17:14 pl sudo:  pluknet : TTY=ttyv1 ; PWD=/usr/home/pluknet
>  >  ; USER=root ; COMMAND=/usr/libexec/getty 3wire.9600 ttyd0
>  >  Mar 17 03:17:14 pl kernel: lock order reversal:
>  >  Mar 17 03:17:14 pl kernel: 1st 0xc07e9274 proctree (proctree) _at_
>  >  /usr/src/sys/kern/kern_exit.c:291
>  >  Mar 17 03:17:14 pl kernel: 2nd 0xc2fc49e8 devfs (devfs) _at_
>  >  /usr/src/sys/kern/vfs_subr.c:2158
>
>
> This one seems interesting.
>  Next time you experience it can you please drop in DDB and print-out
>  the correct order revealed by WITNESS?
>

Fortunately I could reproduce it.

lock order reversal:
 1st 0xc07e9274 proctree (proctree) _at_ /usr/src/sys/kern/kern_exit.c:291
 2nd 0xc3c18278 devfs (devfs) _at_ /usr/src/sys/kern/vfs_subr.c:2158
KDB: stack backtrace:
db_trace_self_wrapper(c07682d0,d6078b24,c0573236,c076a615,c3c18278,...)
at db_trace_self_wrapper+0x26
kdb_backtrace(c076a615,c3c18278,c075bcfb,c075bcfb,c0770a8c,...) at
kdb_backtrace+0x29
witness_checkorder(c3c18278,9,c0770a8c,86e,c07edcd4,...) at
witness_checkorder+0x6d6
_lockmgr_args(c3c18278,20002,c3c182a8,0,ffffffff,...) at _lockmgr_args+0x519
vop_stdlock(d6078bc4,d6078bbc,c0572a1c,20002,c3c182a8,...) at vop_stdlock+0x51
VOP_LOCK1_APV(c07a07e0,d6078bc4,851,d6078be4,c3c182a8,...) at VOP_LOCK1_APV+0xa5
_vn_lock(c3c18220,20002,c0770a8c,86e,4,...) at _vn_lock+0xf2
vrele(c3c18220,0,c07619a2,14e,ffffffff,...) at vrele+0x142
exit1(c2fdd690,0,d6078d2c,c0729ed3,c2fdd690,...) at exit1+0x8a1
sys_exit(c2fdd690,d6078cfc,4,c07625a5,c07a3d38,...) at sys_exit+0x1d
syscall(d6078d38) at syscall+0x2b3
Xint0x80_syscall() at Xint0x80_syscall+0x20
--- syscall (1, FreeBSD ELF32, sys_exit), eip = 0x2811964f, esp =
0xbfbfeacc, ebp = 0xbfbfead8 ---

Something else?

wbr,
pluknet