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=-16.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,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 AF6FCC43461 for ; Thu, 1 Apr 2021 09:38:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6E5CC6044F for ; Thu, 1 Apr 2021 09:38:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233827AbhDAJhg (ORCPT ); Thu, 1 Apr 2021 05:37:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233940AbhDAJhL (ORCPT ); Thu, 1 Apr 2021 05:37:11 -0400 Received: from mail-pf1-x435.google.com (mail-pf1-x435.google.com [IPv6:2607:f8b0:4864:20::435]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A293C061788 for ; Thu, 1 Apr 2021 02:37:11 -0700 (PDT) Received: by mail-pf1-x435.google.com with SMTP id q5so1017990pfh.10 for ; Thu, 01 Apr 2021 02:37:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=mcgJPI+OLnXKS6f2jEHdXibOScXid3UD2wHpcMZsYC8=; b=XXHnwjtjUIXHglDE8sYs3uix5dsEwoiOr126fLR+uD3MRWnDxS5mXundRMl6oyKp8G 0BLCnAd0wZdUTDQv56WayLebeE+LCDZkat3P2QE/0k4sHmu8NBn0RGQRL6DskgayhEpO f7OYOJq4cZf1cTx/cZ9d26eS+5jXRdj/j6OunAYDgBQsW3YFdnLcJadkiiuoPIQepTQz SejeuXsZq8aFLT/CMxOee3LtDWYILC+Tl5e/mZ9gSpTzd8IItpg22a7lTIMUfH+6YlmD ZyTzP9SIX/AQO1VFFJHw8ibEa1T0YPK9AzIhi9n+n+HwhvxGAX+4pSKt25A/Ehm2YWml n8CQ== 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:mime-version :content-transfer-encoding; bh=mcgJPI+OLnXKS6f2jEHdXibOScXid3UD2wHpcMZsYC8=; b=nle1NjZk6tNvc6F5LSRcW+Q9pwWwXxpsGVWBe0oPy2mlaYfp6FWbqX4aXWUqB+oNiy fGg2SzSkVwTvnpWo/KBjA5qdA1e2X3w04Qnze5/8lRKjGJei1fJCYn+Qaxshxtwn65Tc 1WwUxOjPT/csT6RHrcKpK4WlwIrFXVfbIxtDI1062lxLooJMb5p34LYinfgUV0MBXul9 OQSQNTnR6vy9tKEfULjFUIo++oZqTXz+UKPbfIpGaI5IrkbV4dQv9AFKhkDdethjH+AX duqaqZSk5apw9aQdhJdV0Xerk6zZFV1r+W/Wo944jJV1FlhHB+8mhJyx/rU5BXAPHyay QpZQ== X-Gm-Message-State: AOAM532/6bJZF5menlVUscqKplkak0PGGJPyy39fTdfrUk+ie9E5ksUK Ue0DngCvtziSChLGj7ZvKaS5Eg== X-Google-Smtp-Source: ABdhPJxkfP7QA7T16arIV78STn7cljX0N93gxkGF9gMmDTfxUDZogi1r5p1jZl2QT4ir2ZVOhGGaSQ== X-Received: by 2002:a65:4c43:: with SMTP id l3mr6637800pgr.327.1617269831183; Thu, 01 Apr 2021 02:37:11 -0700 (PDT) Received: from localhost.localdomain ([139.177.225.233]) by smtp.gmail.com with ESMTPSA id h13sm4710189pjv.52.2021.04.01.02.37.07 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Apr 2021 02:37:10 -0700 (PDT) From: Muchun Song To: viro@zeniv.linux.org.uk, tj@kernel.org, axboe@fb.com, willy@infradead.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Muchun Song Subject: [PATCH v2] writeback: fix obtain a reference to a freeing memcg css Date: Thu, 1 Apr 2021 17:33:43 +0800 Message-Id: <20210401093343.51299-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org The caller of wb_get_create() should pin the memcg, because wb_get_create() relies on this guarantee. The rcu read lock only can guarantee that the memcg css returned by css_from_id() cannot be released, but the reference of the memcg can be zero. Fix it by holding a reference to the css before calling wb_get_create(). This is not a problem I encountered in the real world. Just the result of a code review. And it is unnecessary to use GFP_ATOMIC, so replace it with GFP_NOIO. Fixes: 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates") Signed-off-by: Muchun Song --- Changelog in v2: 1. Replace GFP_ATOMIC with GFP_NOIO suggested by Matthew. fs/fs-writeback.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index e91980f49388..df7f89f8f771 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -501,16 +501,21 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT) return; - isw = kzalloc(sizeof(*isw), GFP_ATOMIC); + isw = kzalloc(sizeof(*isw), GFP_NOIO); if (!isw) return; /* find and pin the new wb */ rcu_read_lock(); memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys); - if (memcg_css) - isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); + if (memcg_css && !css_tryget(memcg_css)) + memcg_css = NULL; rcu_read_unlock(); + if (!memcg_css) + goto out_free; + + isw->new_wb = wb_get_create(bdi, memcg_css, GFP_NOIO); + css_put(memcg_css); if (!isw->new_wb) goto out_free; -- 2.11.0