From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752247AbaI3UKE (ORCPT ); Tue, 30 Sep 2014 16:10:04 -0400 Received: from one.firstfloor.org ([193.170.194.197]:45306 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751207AbaI3UKC (ORCPT ); Tue, 30 Sep 2014 16:10:02 -0400 Date: Tue, 30 Sep 2014 22:10:00 +0200 From: Andi Kleen To: Peter Zijlstra Cc: Andi Kleen , Andi Kleen , dave@sr71.net, linux-kernel@vger.kernel.org, mingo@kernel.org, eranian@google.com, x86@kernel.org Subject: Re: [PATCH 1/2] Use faster check for modules in backtrace on 64bit Message-ID: <20140930200959.GB8196@two.firstfloor.org> References: <1411774277-4198-1-git-send-email-andi@firstfloor.org> <1411774277-4198-2-git-send-email-andi@firstfloor.org> <20140929114212.GG5430@worktop> <20140929152145.GB1629@tassilo.jf.intel.com> <20140929203023.GA8196@two.firstfloor.org> <20140930085814.GS5430@worktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140930085814.GS5430@worktop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > Also I investigated it now, but we don't have RCU support for rbtrees. > > So it would need some kind of locking for the reader, which is a show > > stopper. > > Nah, we can trivially do that with a seqlock. Not read side locking > required in the normal case. I'm not convinced. It wouldn't surprise me if it was possible to generate endless cycles with rcu freed memory on some rebalancing operation. If you think I'm wrong please show working code. Also please explain clearly for the module maintainers and me what the problem with my original simple trivially show to be correct solution is. Thanks, -Andi -- ak@linux.intel.com -- Speaking for myself only.