From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753700Ab1EIRC5 (ORCPT ); Mon, 9 May 2011 13:02:57 -0400 Received: from lennier.cc.vt.edu ([198.82.162.213]:51360 "EHLO lennier.cc.vt.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752701Ab1EIRCz (ORCPT ); Mon, 9 May 2011 13:02:55 -0400 X-Mailer: exmh version 2.7.2 01/07/2005 with nmh-1.3-dev Cc: Randy Dunlap , Andrew Morton , "Paul E. McKenney" , Lai Jiangshan , linux-kernel@vger.kernel.org Subject: Re: 2.6.39-rc6-mmotm0506 and -next - __kfree_rcu breaks third-party kernel code In-Reply-To: Your message of "Mon, 09 May 2011 12:56:32 EDT." <14010.1304960192@localhost> From: Valdis.Kletnieks@vt.edu References: <7961.1304953500@localhost> <20110509091757.580f3f6c.randy.dunlap@oracle.com> <14010.1304960192@localhost> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1304960536_2759P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Mon, 09 May 2011 13:02:16 -0400 Message-ID: <14344.1304960536@localhost> X-Mirapoint-Received-SPF: 198.82.161.152 auth3.smtp.vt.edu Valdis.Kletnieks@vt.edu 2 pass X-Mirapoint-IP-Reputation: reputation=neutral-1, source=Fixed, refid=n/a, actions=MAILHURDLE SPF TAG X-Junkmail-Status: score=10/50, host=dagger.cc.vt.edu X-Junkmail-Signature-Raw: score=unknown, refid=str=0001.0A020207.4DC81E19.00F5,ss=1,fgs=0, ip=0.0.0.0, so=2010-07-22 22:03:31, dmn=2009-09-10 00:05:08, mode=single engine X-Junkmail-IWF: false To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --==_Exmh_1304960536_2759P Content-Type: text/plain; charset=us-ascii On Mon, 09 May 2011 12:56:32 EDT, Valdis.Kletnieks@vt.edu said: > OK, *now* I'm confused. The magic sauce appears to be "-Os". Adding that makes > the compile work. And for no obvious reason - there's something in there that > causes indigestion, but only if the optimizer isn't invoked. /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/rcupdate.h: In function '__kfree_rcu': /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/rcupdate.h:822:2: error: size of unnamed array is negative Apparently, it's in fact bad code - but the entire __kfree_rcu() function is being reaped by the optimizer as dead code before the code generator sees the size issue with the array. Without optimization, the code hangs around long enough for the problem to crop up. --==_Exmh_1304960536_2759P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Exmh version 2.5 07/13/2001 iD8DBQFNyB4YcC3lWbTT17ARAtMFAJ9SlogAME6VeEfhvUiT1+IPehIDfACeM/2u SDVXwu2FtrXWy8SYFacDx34= =c7/F -----END PGP SIGNATURE----- --==_Exmh_1304960536_2759P--