From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759022AbYB0Tzx (ORCPT ); Wed, 27 Feb 2008 14:55:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758277AbYB0Tzm (ORCPT ); Wed, 27 Feb 2008 14:55:42 -0500 Received: from www.tglx.de ([62.245.132.106]:43804 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758173AbYB0Tzm (ORCPT ); Wed, 27 Feb 2008 14:55:42 -0500 Date: Wed, 27 Feb 2008 20:55:28 +0100 (CET) From: Thomas Gleixner To: David Miller cc: mikpe@it.uu.se, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [BUG] 2.6.25-rc3 hangs in early boot on Sun Ultra5 In-Reply-To: <20080227.110538.160750982.davem@davemloft.net> Message-ID: References: <20080226.164900.193701385.davem@davemloft.net> <20080226.170613.107688605.davem@davemloft.net> <20080227.110538.160750982.davem@davemloft.net> User-Agent: Alpine 1.00 (LFD 882 2007-12-20) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 27 Feb 2008, David Miller wrote: > From: Thomas Gleixner > Date: Wed, 27 Feb 2008 09:02:22 +0100 (CET) > > > On Tue, 26 Feb 2008, David Miller wrote: > > > What the FUTEX checking code is doing now is doing a "user" access > > > with set_fs(KERNEL_DS) since it runs from the kernel bootup early init > > > sequence. And this is illegal according to the existing checks. > > > > > > When we do set_fs(KERNEL_DS) then pass a "user" pointer down > > > into a system call or something like that, we give it a pointer > > > that "cannot fault". So if we get into the fault handling > > > path here for a case like that we really do want to scream and > > > print out an OOPS message in my opinion. > > > > So it would be correct to set_fs(USER_DS) then do the check and switch > > back to KERNEL_DS ? > > No, I'm saying it would be better not to take faults purposefully in > the kernel address space. I would have preferred not to. The hassle is that we need to figure out, whether it works or not _before_ any user space program can use the interfaces. We could omit the check for archs where the in_atomic_cmpxchg is guaranteed to be functional. > We don't have a usable user address space > setup at this point in the boot, so using USER_DS would be even worse. Ouch, yes. Stupid me. > I think I'll just add a different version of the sanity check to this > sparc64 code later on, one that will take into consideration this > KERNEL_DS case because I can see how it could be useful in other > circumstances. Ok. Thanks, tglx