Re: Seeing lock order reversal

2008/3/18, pluknet <pluknet_at_gmail.com>:
> 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?

This is the "2nd order".
It would be nice to get where these locks are acquired and what is the
"1st order".
In order to get it, it is enough to break in DDB and do: show witness
at DDB prompt.

Thanks,
Attilio


-- 
Peace can only be achieved by understanding - A. Einstein