Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754785AbbHLOi3 (ORCPT ); Wed, 12 Aug 2015 10:38:29 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:35372 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752798AbbHLOi2 (ORCPT ); Wed, 12 Aug 2015 10:38:28 -0400 Date: Wed, 12 Aug 2015 16:38:21 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Andy Lutomirski , "ksummit-discuss@lists.linuxfoundation.org" , "linux-kernel@vger.kernel.org" , Christoph Lameter , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Chris Metcalf , Rik van Riel Subject: Re: [BELATED CORE TOPIC] context tracking / nohz / RCU state Message-ID: <20150812143819.GE21542@lerouge> References: <20150811183312.GE3895@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150811183312.GE3895@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1332 Lines: 33 On Tue, Aug 11, 2015 at 11:33:12AM -0700, Paul E. McKenney wrote: > On Tue, Aug 11, 2015 at 10:49:36AM -0700, Andy Lutomirski wrote: > > Some arches may need: > > > > i_am_lame_and_forgot_my_previous_context() > > > > x86 will soon (4.3 or 4.4, depending on how my syscall cleanup goes) > > no longer need that. > > > > Paul says that some arches need something that goes straight from IRQ > > to user mode (?) -- sigh. > > Straight from IRQ to process-level kernel mode. I ran into this in > late 2011, and clearly should have documented exactly what code was > doing this. Something about invoking system calls from within the > kernel on some architectures. > > Hey, if no architectures do this anymore, I could simplify RCU a bit! ;-) That issue has always been a bit foggy to me :-) We never really stated what exactly the issue was. Just performing syscalls from kernel mode shouldn't fiddle with the dynticks count. IIUC, the issue was that some IRQs triggered and never returned. But we certainly can't remove the safety code without clearly identifying the issue... -- 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/