From owner-freebsd-current@FreeBSD.ORG Thu Feb 7 11:04:31 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 1052316A418 for ; Thu, 7 Feb 2008 11:04:31 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mu-out-0910.google.com (mu-out-0910.google.com [209.85.134.184]) by mx1.freebsd.org (Postfix) with ESMTP id 6D2C713C4EA for ; Thu, 7 Feb 2008 11:04:30 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: by mu-out-0910.google.com with SMTP id w9so2501608mue.6 for ; Thu, 07 Feb 2008 03:04:29 -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=bjpJkXUg9KqwhTOD0c8xYiCfddKSPJ2r6kZtEoRLckg=; b=jIMPowEvOyIZqWMGDvKGtezDmXa3lKPLW/RbLMvNjvG/ccqEekTPkoGlnTELL9z4XJfyA1mja+Y1KOT1s44ApD2Rly77st9Icd9QaIr05qEuyBXVxqgz0CL24Q3BnqHLs0LppmepCeyY7+MOXmeszv/8Vh0bDAWIZFJgGYCxVe8= 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=FaFLGziqbwsJL66XWhd9n27S6lYpfHzb5yDmDhZyBqZn8083M+4NWOrcMMv+YCOTy6qA1mUHIOGQf+beDhayUDD4GVjSPZN4iyi+sWCM5YNtk8khEIgGyKHpAvAxpS7aLy+hngA+AuVAH5mGIYqlWEQ4a+BSdtOTMOE7GsUKaH0= Received: by 10.86.62.3 with SMTP id k3mr10282621fga.8.1202382269010; Thu, 07 Feb 2008 03:04:29 -0800 (PST) Received: by 10.86.28.19 with HTTP; Thu, 7 Feb 2008 03:04:28 -0800 (PST) Message-ID: <3bbf2fe10802070304r29cb8d2u1210fe285c917424@mail.gmail.com> Date: Thu, 7 Feb 2008 12:04:28 +0100 From: "Attilio Rao" Sender: asmrookie@gmail.com To: "Kostik Belousov" In-Reply-To: <20080207104354.GY57756@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> X-Google-Sender-Auth: 7fb4a8cb41e727d5 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 11:04:31 -0000 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. Attilio -- Peace can only be achieved by understanding - A. Einstein