Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932317Ab0GIACS (ORCPT ); Thu, 8 Jul 2010 20:02:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2126 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932145Ab0GIAAU (ORCPT ); Thu, 8 Jul 2010 20:00:20 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit From: Roland McGrath To: Oleg Nesterov X-Fcc: ~/Mail/linus Cc: "Paul E. McKenney" , Andrew Morton , Don Zickus , Frederic Weisbecker , Ingo Molnar , Jerome Marchand , Mandeep Singh Baines , linux-kernel@vger.kernel.org, stable@kernel.org, "Eric W. Biederman" Subject: Re: while_each_thread() under rcu_read_lock() is broken? In-Reply-To: Oleg Nesterov's message of Monday, 21 June 2010 22:06:33 +0200 <20100621200633.GA21099@redhat.com> References: <20100618190251.GA17297@redhat.com> <20100618193403.GA17314@redhat.com> <20100618223354.GL2365@linux.vnet.ibm.com> <20100621170919.GA13826@redhat.com> <20100621174455.GA14886@redhat.com> <20100621190212.C8630400C5@magilla.sf.frob.com> <20100621200633.GA21099@redhat.com> X-Zippy-Says: Are we on STRIKE yet? Message-Id: <20100708235925.A71DA4A967@magilla.sf.frob.com> Date: Thu, 8 Jul 2010 16:59:25 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 856 Lines: 19 > We can't do call_rcu(release_task), > we can't take tasklist for writing in the softirq context. But even > if we could, this can't help in fact or I missed something. Ah, I had missed that constraint of call_rcu. (It's not mentioned in the kerneldoc comment directly, and is only buried in a couple of brief mentions in Documentation/RCU/.) I was thinking that would suffice because it does it between rcu_read_lock critical sections, but I guess it actually only does it after the last one and doesn't prevent a new one from having started on another CPU. (And we can't use it anyway.) Thanks, Roland -- 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/