Re: Seeing lock order reversal

* pluknet <pluknet_at_gmail.com> wrote:
> 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?

I also saw this LOR inside my mpsafetty branch in Perforce - it can
easily be fixed by just calling vrele() after the proctree_lock has been
unlocked. I don't have a patch at hand, because I've entirely rewritten
that code.

-- 
 Ed Schouten <ed_at_80386.nl>
 WWW: http://g-rave.nl/