Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933817Ab1FWRih (ORCPT ); Thu, 23 Jun 2011 13:38:37 -0400 Received: from mail.windriver.com ([147.11.1.11]:35521 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933792Ab1FWRia (ORCPT ); Thu, 23 Jun 2011 13:38:30 -0400 From: Paul Gortmaker To: stable@kernel.org, linux-kernel@vger.kernel.org Cc: stable-review@kernel.org, Milton Miller , Linus Torvalds , Paul Gortmaker Subject: [34-longterm 195/247] call_function_many: fix list delete vs add race Date: Thu, 23 Jun 2011 13:34:23 -0400 Message-Id: <1308850515-15242-136-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.4.4 In-Reply-To: <1308850515-15242-1-git-send-email-paul.gortmaker@windriver.com> References: <1308849690-14530-1-git-send-email-paul.gortmaker@windriver.com> <1308850515-15242-1-git-send-email-paul.gortmaker@windriver.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3024 Lines: 77 From: Milton Miller ------------------- This is a commit scheduled for the next v2.6.34 longterm release. If you see a problem with using this for longterm, please comment. ------------------- 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: Paul Gortmaker --- kernel/smp.c | 20 +++++++++++++------- 1 files changed, 13 insertions(+), 7 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 0a9e6bd..de11a66 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -470,14 +470,15 @@ void smp_call_function_many(const struct cpumask *mask, 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)); raw_spin_lock_irqsave(&call_function.lock, flags); /* @@ -486,6 +487,11 @@ void smp_call_function_many(const struct cpumask *mask, * 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)); raw_spin_unlock_irqrestore(&call_function.lock, flags); /* -- 1.7.4.4 -- 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/