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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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=unavailable 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 EF37EC4167B for ; Mon, 13 Sep 2021 14:49:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA76360C51 for ; Mon, 13 Sep 2021 14:49:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348519AbhIMOul (ORCPT ); Mon, 13 Sep 2021 10:50:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:60460 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346229AbhIMOpS (ORCPT ); Mon, 13 Sep 2021 10:45:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 79CF66138D; Mon, 13 Sep 2021 13:58:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631541496; bh=7cPgit04OnoYTxOk+CS+U8wiG3J4aHNe3jVdPZIM02Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=msAVgGT3AC47eIDESfH6a9RQ++3Z14knTnRNxkaduCB5UQCez2+/vrFEZqmdzicWZ XNH2LO6vSKF0XSBTjdCdrOcVSOHkbZB6UZbBYZMiOuCixtwtATVJS0buhZoKjJEjo8 Ou+YOUYgQRdzd+yAmlP+2U1BkFjUBkSKwQy7Z3RI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Xiao Ni , Guoqing Jiang , Song Liu Subject: [PATCH 5.14 321/334] md/raid10: Remove unnecessary rcu_dereference in raid10_handle_discard Date: Mon, 13 Sep 2021 15:16:15 +0200 Message-Id: <20210913131124.279825906@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210913131113.390368911@linuxfoundation.org> References: <20210913131113.390368911@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: linux-kernel@vger.kernel.org From: Xiao Ni commit 46d4703b1db4c86ab5acb2331b10df999f005e8e upstream. We are seeing the following warning in raid10_handle_discard. [ 695.110751] ============================= [ 695.131439] WARNING: suspicious RCU usage [ 695.151389] 4.18.0-319.el8.x86_64+debug #1 Not tainted [ 695.174413] ----------------------------- [ 695.192603] drivers/md/raid10.c:1776 suspicious rcu_dereference_check() usage! [ 695.225107] other info that might help us debug this: [ 695.260940] rcu_scheduler_active = 2, debug_locks = 1 [ 695.290157] no locks held by mkfs.xfs/10186. In the first loop of function raid10_handle_discard. It already determines which disk need to handle discard request and add the rdev reference count rdev->nr_pending. So the conf->mirrors will not change until all bios come back from underlayer disks. It doesn't need to use rcu_dereference to get rdev. Cc: stable@vger.kernel.org Fixes: d30588b2731f ('md/raid10: improve raid10 discard request') Signed-off-by: Xiao Ni Acked-by: Guoqing Jiang Signed-off-by: Song Liu Signed-off-by: Greg Kroah-Hartman --- drivers/md/raid10.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -1712,6 +1712,11 @@ retry_discard: } else r10_bio->master_bio = (struct bio *)first_r10bio; + /* + * first select target devices under rcu_lock and + * inc refcount on their rdev. Record them by setting + * bios[x] to bio + */ rcu_read_lock(); for (disk = 0; disk < geo->raid_disks; disk++) { struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev); @@ -1743,9 +1748,6 @@ retry_discard: for (disk = 0; disk < geo->raid_disks; disk++) { sector_t dev_start, dev_end; struct bio *mbio, *rbio = NULL; - struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev); - struct md_rdev *rrdev = rcu_dereference( - conf->mirrors[disk].replacement); /* * Now start to calculate the start and end address for each disk. @@ -1775,9 +1777,12 @@ retry_discard: /* * It only handles discard bio which size is >= stripe size, so - * dev_end > dev_start all the time + * dev_end > dev_start all the time. + * It doesn't need to use rcu lock to get rdev here. We already + * add rdev->nr_pending in the first loop. */ if (r10_bio->devs[disk].bio) { + struct md_rdev *rdev = conf->mirrors[disk].rdev; mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set); mbio->bi_end_io = raid10_end_discard_request; mbio->bi_private = r10_bio; @@ -1790,6 +1795,7 @@ retry_discard: bio_endio(mbio); } if (r10_bio->devs[disk].repl_bio) { + struct md_rdev *rrdev = conf->mirrors[disk].replacement; rbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set); rbio->bi_end_io = raid10_end_discard_request; rbio->bi_private = r10_bio;