Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755175AbZAMWNb (ORCPT ); Tue, 13 Jan 2009 17:13:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754846AbZAMWNW (ORCPT ); Tue, 13 Jan 2009 17:13:22 -0500 Received: from krynn.se.axis.com ([193.13.178.10]:51644 "EHLO krynn.se.axis.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753825AbZAMWNV (ORCPT ); Tue, 13 Jan 2009 17:13:21 -0500 Date: Tue, 13 Jan 2009 23:12:35 +0100 From: Jesper Nilsson To: David Miller Cc: "tj@kernel.org" , "gregkh@suse.de" , "stern@rowland.harvard.edu" , "jens.axboe@oracle.com" , "hinko.kocevar@cetrtapot.si" , "linux-kernel@vger.kernel.org" Subject: Re: lib/klist.c: bit 0 in pointer can't be used as flag Message-ID: <20090113221235.GD19262@axis.com> References: <20090113151406.GC19262@axis.com> <20090113.131030.207355839.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090113.131030.207355839.davem@davemloft.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1317 Lines: 32 On Tue, Jan 13, 2009 at 10:10:30PM +0100, David Miller wrote: > From: Jesper Nilsson > Date: Tue, 13 Jan 2009 16:14:06 +0100 > > > The commit a1ed5b0cffe4b16a93a6a3390e8cee0fbef94f86 > > (klist: don't iterate over deleted entries) introduces use of the > > low bit in a pointer to indicate if the knode is dead or not, > > assuming that this bit is always free. > > > > This is not true for all architectures, CRIS for example may align data > > on byte borders. > > There are many other spots in the kernel where the low bits of a > pointer are hijacked as status bits. Lots of other things cannot > possible be working on CRIS because of this. It may be that we've worked around the other spots, although I haven't seen anything like that, we might just have been lucky until now. Can you recall another place where this trick is used? It seems that rt_mutex uses the same trick (with the lowest 2bits) but AFAICT that's something we don't use on CRIS. /^JN - Jesper Nilsson -- Jesper Nilsson -- jesper.nilsson@axis.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/