From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757248AbYIIT5a (ORCPT ); Tue, 9 Sep 2008 15:57:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754236AbYIIT5W (ORCPT ); Tue, 9 Sep 2008 15:57:22 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:54859 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753976AbYIIT5V (ORCPT ); Tue, 9 Sep 2008 15:57:21 -0400 Date: Tue, 09 Sep 2008 12:57:14 -0700 (PDT) Message-Id: <20080909.125714.35737132.davem@davemloft.net> To: manfred@colorfullife.com Cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, wli@holomorphy.com, sparclinux@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [PATCH] prevent sparc64 from invoking irq handlers on offline CPUs From: David Miller In-Reply-To: <48C6C520.5070103@colorfullife.com> References: <20080903154217.GA6807@linux.vnet.ibm.com> <20080908.171708.43575256.davem@davemloft.net> <48C6C520.5070103@colorfullife.com> X-Mailer: Mew version 6.1 on Emacs 22.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Manfred Spraul Date: Tue, 09 Sep 2008 20:49:04 +0200 > David Miller wrote: > > And IPI handler runs in HW irq context, therefore such an IPI-creates-an-IPI > > should not be allowed, at least not directly. > > > > Actually the restriction seems to be that an IPI cannot be sent when > > "irqs_disabled()", hmmm... > > > > > Does this apply to smp_send_reschedule() as well? > A [rare] codepath in the current rcu code does to trigger quiescent states on remote cpus. It does work on sparc64. Such an IPI doesn't do a wait so there would be no deadlock issues either.