From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755072Ab2BEWrr (ORCPT ); Sun, 5 Feb 2012 17:47:47 -0500 Received: from 1wt.eu ([62.212.114.60]:61864 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753695Ab2BEW0S (ORCPT ); Sun, 5 Feb 2012 17:26:18 -0500 Message-Id: <20120205220950.642723239@pcw.home.local> User-Agent: quilt/0.48-1 Date: Sun, 05 Feb 2012 23:10:17 +0100 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jens Axboe , Greg KH Subject: [PATCH 28/91] cfq-iosched: fix locking around ioc->ioc_data assignment In-Reply-To: <0635750f5f06ed2ca212b91fcb5c4483@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.27-longterm review patch. If anyone has any objections, please let us know. ------------------ commit ab4bd22d3cce6977dc039664cc2d052e3147d662 upstream. Since we are modifying this RCU pointer, we need to hold the lock protecting it around it. This fixes a potential reuse and double free of a cfq io_context structure. The bug has been in CFQ for a long time, it hit very few people but those it did hit seemed to see it a lot. Tracked in RH bugzilla here: https://bugzilla.redhat.com/show_bug.cgi?id=577968 Credit goes to Paul Bolle for figuring out that the issue was around the one-hit ioc->ioc_data cache. Thanks to his hard work the issue is now fixed. Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/cfq-iosched.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) Index: longterm-2.6.27/block/cfq-iosched.c =================================================================== --- longterm-2.6.27.orig/block/cfq-iosched.c 2012-02-05 22:34:34.185915429 +0100 +++ longterm-2.6.27/block/cfq-iosched.c 2012-02-05 22:34:38.850917663 +0100 @@ -1286,8 +1286,11 @@ cic->dead_key = (unsigned long) cic->key; cic->key = NULL; - if (ioc->ioc_data == cic) + if (rcu_dereference(ioc->ioc_data) == cic) { + spin_lock(&ioc->lock); rcu_assign_pointer(ioc->ioc_data, NULL); + spin_unlock(&ioc->lock); + } if (cic->cfqq[ASYNC]) { cfq_exit_cfqq(cfqd, cic->cfqq[ASYNC]);