From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8DD56C4332D for ; Mon, 11 Jan 2021 13:24:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 62E052225E for ; Mon, 11 Jan 2021 13:24:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728804AbhAKNYL (ORCPT ); Mon, 11 Jan 2021 08:24:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:35538 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732663AbhAKNRl (ORCPT ); Mon, 11 Jan 2021 08:17:41 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id B271D2246B; Mon, 11 Jan 2021 13:17:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1610371045; bh=ZC8biu2rBnDrTjnIWiaDeoITdh+U0ptR2jeWui5ivvc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uf014tLUb5JzG4yAKlgXA7DpmXpB0KbjnqPzs/MUv9aV/3QPrwiiig+NKp+zEtHgb o7XU+69Zks4jPzo5EmAdoc5SdC//h1QnpFl0MZ4y4yw3n9bejwSfbMbCbD1o2L8V1R FcfOsLXnslsOsUOUYqAm6JbJzvJbyQg9NAogJvv4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tejun Heo , Jonathan Lemon , Jens Axboe Subject: [PATCH 5.10 117/145] blk-iocost: fix NULL iocg deref from racing against initialization Date: Mon, 11 Jan 2021 14:02:21 +0100 Message-Id: <20210111130054.150102299@linuxfoundation.org> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210111130048.499958175@linuxfoundation.org> References: <20210111130048.499958175@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Tejun Heo commit d16baa3f1453c14d680c5fee01cd122a22d0e0ce upstream. When initializing iocost for a queue, its rqos should be registered before the blkcg policy is activated to allow policy data initiailization to lookup the associated ioc. This unfortunately means that the rqos methods can be called on bios before iocgs are attached to all existing blkgs. While the race is theoretically possible on ioc_rqos_throttle(), it mostly happened in ioc_rqos_merge() due to the difference in how they lookup ioc. The former determines it from the passed in @rqos and then bails before dereferencing iocg if the looked up ioc is disabled, which most likely is the case if initialization is still in progress. The latter looked up ioc by dereferencing the possibly NULL iocg making it a lot more prone to actually triggering the bug. * Make ioc_rqos_merge() use the same method as ioc_rqos_throttle() to look up ioc for consistency. * Make ioc_rqos_throttle() and ioc_rqos_merge() test for NULL iocg before dereferencing it. * Explain the danger of NULL iocgs in blk_iocost_init(). Signed-off-by: Tejun Heo Reported-by: Jonathan Lemon Cc: stable@vger.kernel.org # v5.4+ Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/blk-iocost.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -2525,8 +2525,8 @@ static void ioc_rqos_throttle(struct rq_ bool use_debt, ioc_locked; unsigned long flags; - /* bypass IOs if disabled or for root cgroup */ - if (!ioc->enabled || !iocg->level) + /* bypass IOs if disabled, still initializing, or for root cgroup */ + if (!ioc->enabled || !iocg || !iocg->level) return; /* calculate the absolute vtime cost */ @@ -2653,14 +2653,14 @@ static void ioc_rqos_merge(struct rq_qos struct bio *bio) { struct ioc_gq *iocg = blkg_to_iocg(bio->bi_blkg); - struct ioc *ioc = iocg->ioc; + struct ioc *ioc = rqos_to_ioc(rqos); sector_t bio_end = bio_end_sector(bio); struct ioc_now now; u64 vtime, abs_cost, cost; unsigned long flags; - /* bypass if disabled or for root cgroup */ - if (!ioc->enabled || !iocg->level) + /* bypass if disabled, still initializing, or for root cgroup */ + if (!ioc->enabled || !iocg || !iocg->level) return; abs_cost = calc_vtime_cost(bio, iocg, true); @@ -2837,6 +2837,12 @@ static int blk_iocost_init(struct reques ioc_refresh_params(ioc, true); spin_unlock_irq(&ioc->lock); + /* + * rqos must be added before activation to allow iocg_pd_init() to + * lookup the ioc from q. This means that the rqos methods may get + * called before policy activation completion, can't assume that the + * target bio has an iocg associated and need to test for NULL iocg. + */ rq_qos_add(q, rqos); ret = blkcg_activate_policy(q, &blkcg_policy_iocost); if (ret) {