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=-2.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,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 62454C433F4 for ; Fri, 31 Aug 2018 20:23:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E51D2083F for ; Fri, 31 Aug 2018 20:23:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bZuVkyCU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1E51D2083F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727734AbeIAAch (ORCPT ); Fri, 31 Aug 2018 20:32:37 -0400 Received: from mail-yw1-f66.google.com ([209.85.161.66]:36669 "EHLO mail-yw1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727318AbeIAAcg (ORCPT ); Fri, 31 Aug 2018 20:32:36 -0400 Received: by mail-yw1-f66.google.com with SMTP id w202-v6so5504365yww.3; Fri, 31 Aug 2018 13:23:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=4ycn/g7fw8SqfXjt7f6eHXQQdDKhRrTOaowx1xDnWeg=; b=bZuVkyCU1I70NNU/Nt6qA+o76T3OmFM2XGSQlTC/lPJT7C5jA/ts+UF53fAXi4g3tG 0Q2vQwCwAOE53QDwEOSFpaV0duuAdctBWbjH9Z+cZK5/PkbO2nqkAnO2Zz5Hj6REO2B2 Q771+5202p1QLs/shU8sZyELGxXPSy33lvsMWYvYk9LLDCwyJdcJDjgR432TelMGTm4n 2wcf8pmAJUalwtdh61M77DtcLaXCGL0/saDQ++CaWXD67LXH+uu58ycs24LQgz+/5fEy 1D3UR5eGeoKR8zwFnozt+gSTc0I6HMXMVho2482Fx0l6F8WBILRUmnmUpUJUODnwdPfn pG0g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=4ycn/g7fw8SqfXjt7f6eHXQQdDKhRrTOaowx1xDnWeg=; b=BoA2xCGsil8YwmvnYgetz0IuLSFxemh0G2J+nYQDjVLeSCaGVBdraI39HmC/a79wwb 2FnYd6hEZBHSHTo24vdixwmFYib5cY+GQReA8qGA0/nQ+KUFhXhd9EP2jNoClKoZ+MlZ +vitm/qRKJOGgWKIaq+r737VIv1WXsei0VkPsCGUmkWAoGzMB0vwEB4Fk693PrFASH0d Eykly9EfTnXMxPMWcKgzuu7C1GyOwJY0jSPGv/KOSLWGZBl58cx4BTYb5jadw+KK/VRq 2HmAhTF2WNkXMJi8Mtxtizp8AGG9MRQpYaG9B4iQQOynJW17fhMWYji8uVJiUt/UAGhy UAgA== X-Gm-Message-State: APzg51BEhgsOZJl9rHEurOGNfBd9NF/zGq2oyOjmBnAq0S1NUzf88XXF cF+Ojogbk36jBQ3MyLHba5o= X-Google-Smtp-Source: ANB0VdY+INE7johEGMkgFOBITRvMMUq2y/hHmr0PxjzoXJtN4liPNWMZ/bvDc1K2PXwkRFnyuvGaFw== X-Received: by 2002:a81:1151:: with SMTP id 78-v6mr9772760ywr.138.1535747009349; Fri, 31 Aug 2018 13:23:29 -0700 (PDT) Received: from dennisz-mbp.thefacebook.com ([199.201.65.129]) by smtp.gmail.com with ESMTPSA id u8-v6sm3978961ywl.59.2018.08.31.13.23.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 31 Aug 2018 13:23:28 -0700 (PDT) From: Dennis Zhou To: Jens Axboe , Tejun Heo , Johannes Weiner , Josef Bacik Cc: kernel-team@fb.com, linux-block@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, "Dennis Zhou (Facebook)" , Jiufei Xue , Joseph Qi Subject: [PATCH 3/3] blkcg: use tryget logic when associating a blkg with a bio Date: Fri, 31 Aug 2018 16:22:44 -0400 Message-Id: <20180831202244.21678-4-dennisszhou@gmail.com> X-Mailer: git-send-email 2.13.5 In-Reply-To: <20180831202244.21678-1-dennisszhou@gmail.com> References: <20180831202244.21678-1-dennisszhou@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Dennis Zhou (Facebook)" There is a very small change a bio gets caught up in a really unfortunate race between a task migration, cgroup exiting, and itself trying to associate with a blkg. This is due to css offlining being performed after the css->refcnt is killed which triggers removal of blkgs that reach their blkg->refcnt of 0. To avoid this, association with a blkg should use tryget and fallback to using the root_blkg. v2: - In blk-throttle, be explicit that we only associate with the root_blkg if tryget failed. Fixes: 08e18eab0c579 ("block: add bi_blkg to the bio for cgroups") Signed-off-by: Dennis Zhou Cc: Jiufei Xue Cc: Joseph Qi Cc: Tejun Heo Cc: Josef Bacik Cc: Jens Axboe --- block/bio.c | 3 ++- block/blk-throttle.c | 5 +++-- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/block/bio.c b/block/bio.c index 04969b392c72..4473ccd22987 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1987,7 +1987,8 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg) { if (unlikely(bio->bi_blkg)) return -EBUSY; - blkg_get(blkg); + if (!blkg_try_get(blkg)) + return -ENODEV; bio->bi_blkg = blkg; return 0; } diff --git a/block/blk-throttle.c b/block/blk-throttle.c index a3eede00d302..01d0620a4e4a 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -2129,8 +2129,9 @@ static inline void throtl_update_latency_buckets(struct throtl_data *td) static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio) { #ifdef CONFIG_BLK_DEV_THROTTLING_LOW - if (bio->bi_css) - bio_associate_blkg(bio, tg_to_blkg(tg)); + /* fallback to root_blkg if we fail to get a blkg ref */ + if (bio->bi_css && (bio_associate_blkg(bio, tg_to_blkg(tg)) == -ENODEV)) + bio_associate_blkg(bio, bio->bi_disk->queue->root_blkg); bio_issue_init(&bio->bi_issue, bio_sectors(bio)); #endif } -- 2.17.1