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=-18.9 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 D8E8FC4743F for ; Tue, 8 Jun 2021 01:31:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8C8F561002 for ; Tue, 8 Jun 2021 01:31:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C8F561002 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=fb.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 505F06B0074; Mon, 7 Jun 2021 21:31:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 43ED66B0075; Mon, 7 Jun 2021 21:31:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 293EF6B0078; Mon, 7 Jun 2021 21:31:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0133.hostedemail.com [216.40.44.133]) by kanga.kvack.org (Postfix) with ESMTP id E268F6B0074 for ; Mon, 7 Jun 2021 21:31:45 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 7DFD6181AEF0B for ; Tue, 8 Jun 2021 01:31:45 +0000 (UTC) X-FDA: 78228829770.28.62B8B12 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by imf29.hostedemail.com (Postfix) with ESMTP id 903F2544 for ; Tue, 8 Jun 2021 01:31:40 +0000 (UTC) Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 1581QEJA013114 for ; Mon, 7 Jun 2021 18:31:43 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding : content-type; s=facebook; bh=5HrHHih5juBqYKEEslPOvXicus6WWgPH+iRjEl6TblE=; b=amxgprEku9rCQRvdWBmXu/0dZv4ziiDbMNJ1H+AzjZDyEK4MCtAofsB8BWqiwnlGlCV9 o+B9DsMRcSyLKfce86LYlR5S/ijO3IKbacOzZzKQS6pN5fgSUruVQ1CbruTOxl2VYpSn iwWuHMNyDlaII8Zrs4IKhdjvpmJnmWPwVlk= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 390rxb9fju-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Mon, 07 Jun 2021 18:31:43 -0700 Received: from intmgw001.05.prn6.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Mon, 7 Jun 2021 18:31:41 -0700 Received: by devvm3388.prn0.facebook.com (Postfix, from userid 111017) id 9090781D6D45; Mon, 7 Jun 2021 18:31:29 -0700 (PDT) From: Roman Gushchin To: Jan Kara , Tejun Heo CC: , , , Alexander Viro , Dennis Zhou , Dave Chinner , , Roman Gushchin Subject: [PATCH v8 2/8] writeback, cgroup: add smp_mb() to cgroup_writeback_umount() Date: Mon, 7 Jun 2021 18:31:17 -0700 Message-ID: <20210608013123.1088882-3-guro@fb.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210608013123.1088882-1-guro@fb.com> References: <20210608013123.1088882-1-guro@fb.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-GUID: xI6nemlGnc0PS17WIQoaRHQuT3EwsAOh X-Proofpoint-ORIG-GUID: xI6nemlGnc0PS17WIQoaRHQuT3EwsAOh X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-06-08_01:2021-06-04,2021-06-08 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 impostorscore=0 lowpriorityscore=0 adultscore=0 mlxscore=0 phishscore=0 mlxlogscore=693 suspectscore=0 clxscore=1015 bulkscore=0 malwarescore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106080007 X-FB-Internal: deliver X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 903F2544 X-Stat-Signature: f3fxijx9b85tg3ttcsmm5xih5wrkpfcc Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=fb.com header.s=facebook header.b=amxgprEk; dmarc=pass (policy=reject) header.from=fb.com; spf=pass (imf29.hostedemail.com: domain of "prvs=5793bd417c=guro@fb.com" designates 67.231.145.42 as permitted sender) smtp.mailfrom="prvs=5793bd417c=guro@fb.com" X-HE-Tag: 1623115900-777729 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: A full memory barrier is required between clearing SB_ACTIVE flag in generic_shutdown_super() and checking isw_nr_in_flight in cgroup_writeback_umount(), otherwise a new switch operation might be scheduled after atomic_read(&isw_nr_in_flight) returned 0. This would result in a non-flushed isw_wq, and a potential crash. The problem hasn't yet been seen in the real life and was discovered by Jan Kara by looking into the code. Suggested-by: Jan Kara Signed-off-by: Roman Gushchin --- fs/fs-writeback.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index bd99890599e0..3564efcc4b78 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1000,6 +1000,12 @@ int cgroup_writeback_by_id(u64 bdi_id, int memcg_i= d, unsigned long nr, */ void cgroup_writeback_umount(void) { + /* + * SB_ACTIVE should be reliably cleared before checking + * isw_nr_in_flight, see generic_shutdown_super(). + */ + smp_mb(); + if (atomic_read(&isw_nr_in_flight)) { /* * Use rcu_barrier() to wait for all pending callbacks to --=20 2.31.1