From owner-freebsd-current@FreeBSD.ORG Thu Feb 7 14:11:48 2008 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 8C10B16A41A for ; Thu, 7 Feb 2008 14:11:48 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from fk-out-0910.google.com (fk-out-0910.google.com [209.85.128.188]) by mx1.freebsd.org (Postfix) with ESMTP id F232E13C469 for ; Thu, 7 Feb 2008 14:11:47 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: by fk-out-0910.google.com with SMTP id b27so3718678fka.11 for ; Thu, 07 Feb 2008 06:11:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; bh=dFJGdtatpQjsWAOKEEbIqLVO5isX6d/cm+UomE4AUtQ=; b=uXxNBLuN16fsXtF4TU4hOK34oE+3hZ33r+072Dk16VUGX1Q1w/at8/x99iE4B/iVkwrSpncTFSmwnqnsz/7W/bbxoymGuCiTnVBkRP4Xd6yw0BQI+QgTXyJotg+kUjd72Ggkp0h1o1fvx87I7KmwXxnAz7ABvnm4mCqeiwub9No= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=iLQxsIK5oENwZyQ60xxwBjmLCGbWc2KC3pMVITgNT18/TaqI4wZe/YPabvOKPqVXHVaNob23rhb9/DWFGaG70r33fS3AY3rD9h0vOlq/FY3h9m4QalenAE0L8zCskcj1g5LMgQElAzHog8OZ92GiTvuqv5RJpE3CP4YS3KnxQTk= Received: by 10.82.162.14 with SMTP id k14mr20567017bue.32.1202393506303; Thu, 07 Feb 2008 06:11:46 -0800 (PST) Received: by 10.86.28.19 with HTTP; Thu, 7 Feb 2008 06:11:46 -0800 (PST) Message-ID: <3bbf2fe10802070611v6c7714b5y18bef10d586944c4@mail.gmail.com> Date: Thu, 7 Feb 2008 15:11:46 +0100 From: "Attilio Rao" Sender: asmrookie@gmail.com To: "Kostik Belousov" In-Reply-To: <20080207125252.GC57756@deviant.kiev.zoral.com.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080207045015.GW57756@deviant.kiev.zoral.com.ua> <3bbf2fe10802070216idd5206ey7a66c0873311e66c@mail.gmail.com> <20080207104354.GY57756@deviant.kiev.zoral.com.ua> <3bbf2fe10802070304r29cb8d2u1210fe285c917424@mail.gmail.com> <20080207110901.GZ57756@deviant.kiev.zoral.com.ua> <3bbf2fe10802070421m3a3152a3m6c9aa67d649107e4@mail.gmail.com> <20080207125252.GC57756@deviant.kiev.zoral.com.ua> X-Google-Sender-Auth: ec19523837b15fc4 Cc: Marcel Moolenaar , current@freebsd.org Subject: Re: Old LOR between devfs & devfsmount resurfacing? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 07 Feb 2008 14:11:48 -0000 2008/2/7, Kostik Belousov : > On Thu, Feb 07, 2008 at 01:21:09PM +0100, Attilio Rao wrote: > > 2008/2/7, Kostik Belousov : > > > On Thu, Feb 07, 2008 at 12:04:28PM +0100, Attilio Rao wrote: > > > > 2008/2/7, Kostik Belousov : > > > > > On Thu, Feb 07, 2008 at 11:16:08AM +0100, Attilio Rao wrote: > > > > > > 2008/2/7, Kostik Belousov : > > > > > > > On Wed, Feb 06, 2008 at 11:11:06AM -0800, Marcel Moolenaar wrote: > > > > > > > > All, > > > > > > > > > > > > > > > > I just ran into the following LOR after upgrading my PowerPC box: > > > > > > > > > > > > > > > > lock order reversal: > > > > > > > > 1st 0xdbee94 devfs (devfs) @ /nfs/freebsd/8.x/src/sys/kern/ > > > > > > > > vfs_subr.c:2061 > > > > > > > > 2nd 0xdfb014 devfsmount (devfsmount) @ /nfs/freebsd/8.x/src/sys/fs/ > > > > > > > > devfs/devfs_vnops.c:201 > > > > > > > > KDB: stack backtrace: > > > > > > > > 0xdc0febc8: at kdb_backtrace+0x4c > > > > > > > > 0xdc0febd8: at witness_checkorder+0x704 > > > > > > > > 0xdc0fec28: at _sx_xlock+0x8c > > > > > > > > 0xdc0fec48: at devfs_allocv+0x138 > > > > > > > > 0xdc0fec88: at devfs_root+0x5c > > > > > > > > 0xdc0fecb8: at set_rootvnode+0x44 > > > > > > > > 0xdc0fece8: at vfs_mountroot+0x344 > > > > > > > > 0xdc0fed48: at start_init+0x88 > > > > > > > > 0xdc0feda8: at fork_exit+0xb4 > > > > > > > > 0xdc0fedc8: at fork_trampoline+0xc > > > > > > > > KDB: enter: witness_checkorder > > > > > > > > [thread pid 1 tid 100001 ] > > > > > > > > Stopped at 0x28ee68: addi r0, r0, 0x0 > > > > > > > > > > > > > > > > It seems that this is a LOR reported in 2006 and fixed > > > > > > > > in 2006 as well. Do other people see this too, or should > > > > > > > > I suspect my sources? > > > > > > > > > > > > > > > > > > > > > I believe this is a false positive, caused by the way the witness works. > > > > > > > Attilio recently added the witness support for the lockmgr, that caused > > > > > > > this and at least two more LORs to be printed on startup. > > > > > > > > > > > > > > Correct lock order is devfs vnode -> devfs mount sx lock. When > > > > > > > allocating new devfs vnode, see devfs_allocv(), the newly created > > > > > > > vnode is locked while devfs mount lock already held (see line 250 of > > > > > > > fs/devfs/devfs_vnops.c). Nonetheless, this cannot cause deadlock since > > > > > > > no other thread can find the new vnode, and thus perform the other lock > > > > > > > order for this vnode lock. > > > > > > > > > > > > > > The fix is to shut the witness in this particular case. Attilio, how to > > > > > > > do this ? > > > > > > > > > > > > Just add LK_NOWITNESS for one of the lock involved in the lockinit(). > > > > > > > > > > > > > > > Then, we loss the useful reports of the actual LORs later, isn't it ? > > > > > > > > Another solution would be to rewamp BLESSING option which allow to > > > > 'bless' some LORs. > > > > jhb and me, btw, didn't want to enable it because it could lead some > > > > less experienced developer to hide LORs under this label and this is > > > > something we want to avoid. > > > > > > > > > This LOR shall not be ignored globally. When real, it caused the easily > > > reproducable lockup of the machine. > > > > > > It would be better to introduce some lockmgr flag to ignore _this_ locking. > > > > flag to pass where? > To the lockmgr itself at the point of aquisition, like > lockmgr(&lk, LK_EXCLUSIVE | LK_INTERLOCK | LK_NOWARN, &interlk, ...); No, I really want a general WITNESS support for this (as I also think that having something more fine grained than BLESSING will break all concerns jhb and me are considering now). A simple way to do it would mean hard-coding file and line in a witness table. While file is ok, line makes trouble so we should find an alternative way to do this. Otherwise we can consider skiping checks for a whole function, this should be not so difficult to achive. I need to think more about this. Attilio -- Peace can only be achieved by understanding - A. Einstein