From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756029Ab1CUX5B (ORCPT ); Mon, 21 Mar 2011 19:57:01 -0400 Received: from kroah.org ([198.145.64.141]:49101 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755077Ab1CUXOD (ORCPT ); Mon, 21 Mar 2011 19:14:03 -0400 X-Mailbox-Line: From gregkh@clark.kroah.org Mon Mar 21 16:10:54 2011 Message-Id: <20110321231053.952858129@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Mon, 21 Mar 2011 16:10:12 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Milton Miller Subject: [32/44] call_function_many: fix list delete vs add race In-Reply-To: <20110321231105.GA1744@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm review patch. If anyone has any objections, please let us know. ------------------ From: Milton Miller commit e6cd1e07a185d5f9b0aa75e020df02d3c1c44940 upstream. Peter pointed out there was nothing preventing the list_del_rcu in smp_call_function_interrupt from running before the list_add_rcu in smp_call_function_many. Fix this by not setting refs until we have gotten the lock for the list. Take advantage of the wmb in list_add_rcu to save an explicit additional one. I tried to force this race with a udelay before the lock & list_add and by mixing all 64 online cpus with just 3 random cpus in the mask, but was unsuccessful. Still, inspection shows a valid race, and the fix is a extension of the existing protection window in the current code. Reported-by: Peter Zijlstra Signed-off-by: Milton Miller Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/smp.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) --- a/kernel/smp.c +++ b/kernel/smp.c @@ -429,14 +429,15 @@ void smp_call_function_many(const struct cpumask_clear_cpu(this_cpu, data->cpumask); /* - * To ensure the interrupt handler gets an complete view - * we order the cpumask and refs writes and order the read - * of them in the interrupt handler. In addition we may - * only clear our own cpu bit from the mask. + * We reuse the call function data without waiting for any grace + * period after some other cpu removes it from the global queue. + * This means a cpu might find our data block as it is writen. + * The interrupt handler waits until it sees refs filled out + * while its cpu mask bit is set; here we may only clear our + * own cpu mask bit, and must wait to set refs until we are sure + * previous writes are complete and we have obtained the lock to + * add the element to the queue. */ - smp_wmb(); - - atomic_set(&data->refs, cpumask_weight(data->cpumask)); spin_lock_irqsave(&call_function.lock, flags); /* @@ -445,6 +446,11 @@ void smp_call_function_many(const struct * will not miss any other list entries: */ list_add_rcu(&data->csd.list, &call_function.queue); + /* + * We rely on the wmb() in list_add_rcu to order the writes + * to func, data, and cpumask before this write to refs. + */ + atomic_set(&data->refs, cpumask_weight(data->cpumask)); spin_unlock_irqrestore(&call_function.lock, flags); /*