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=-15.8 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 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 9F2C7C11F68 for ; Tue, 29 Jun 2021 02:35:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8742061D07 for ; Tue, 29 Jun 2021 02:35:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231717AbhF2CiM (ORCPT ); Mon, 28 Jun 2021 22:38:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:58870 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231332AbhF2CiL (ORCPT ); Mon, 28 Jun 2021 22:38:11 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7A8BA61A2B; Tue, 29 Jun 2021 02:35:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1624934144; bh=96wDbcnxKvEndH/L2h+k5iFhgu/tTXngNh5JLFQ2CcU=; h=Date:From:To:Subject:In-Reply-To:From; b=HzZwsvQ6BySQ/7C5eDf5Oz9VzXWnXT0m62e7PelcYaoREitgD/DbVRcsX6/vK17P5 TS8TVowLClnub+oKl/P+w0GxIcvlnZ5akyKEoxspDasoObKtC+zGs8wGAfnitZU3w5 oVD0lmrENffpIsvdZLLiWx11EAUB7gpOr6QbFWdQ= Date: Mon, 28 Jun 2021 19:35:44 -0700 From: Andrew Morton To: akpm@linux-foundation.org, axboe@kernel.dk, dchinner@redhat.com, dennis@kernel.org, guro@fb.com, jack@suse.com, jack@suse.cz, linux-mm@kvack.org, mm-commits@vger.kernel.org, tj@kernel.org, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk Subject: [patch 047/192] writeback, cgroup: add smp_mb() to cgroup_writeback_umount() Message-ID: <20210629023544.cIp9bdGHo%akpm@linux-foundation.org> In-Reply-To: <20210628193256.008961950a714730751c1423@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Roman Gushchin Subject: writeback, cgroup: add smp_mb() to cgroup_writeback_umount() 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. Link: https://lkml.kernel.org/r/20210608230225.2078447-3-guro@fb.com Signed-off-by: Roman Gushchin Suggested-by: Jan Kara Reviewed-by: Jan Kara Cc: Alexander Viro Cc: Dave Chinner Cc: Dennis Zhou Cc: Jan Kara Cc: Tejun Heo Cc: Jens Axboe Signed-off-by: Andrew Morton --- fs/fs-writeback.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/fs-writeback.c~writeback-cgroup-add-smp_mb-to-cgroup_writeback_umount +++ a/fs/fs-writeback.c @@ -1000,6 +1000,12 @@ out_bdi_put: */ 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 _