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=-17.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT, USER_IN_DEF_DKIM_WL 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 CC3B3C3F2D1 for ; Mon, 2 Mar 2020 20:31:23 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8C1AF22B48 for ; Mon, 2 Mar 2020 20:31:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="EmoWHNnC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C1AF22B48 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0C1DE6B0005; Mon, 2 Mar 2020 15:31:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 073506B0006; Mon, 2 Mar 2020 15:31:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ECAD86B0007; Mon, 2 Mar 2020 15:31:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0228.hostedemail.com [216.40.44.228]) by kanga.kvack.org (Postfix) with ESMTP id D89A66B0005 for ; Mon, 2 Mar 2020 15:31:22 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id ABF10180AD804 for ; Mon, 2 Mar 2020 20:31:22 +0000 (UTC) X-FDA: 76551567204.05.fruit27_bfb04228c44d X-HE-Tag: fruit27_bfb04228c44d X-Filterd-Recvd-Size: 5507 Received: from mail-yw1-f74.google.com (mail-yw1-f74.google.com [209.85.161.74]) by imf36.hostedemail.com (Postfix) with ESMTP for ; Mon, 2 Mar 2020 20:31:22 +0000 (UTC) Received: by mail-yw1-f74.google.com with SMTP id w185so932654ywa.22 for ; Mon, 02 Mar 2020 12:31:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=aihQYJyYU6rAhab/wfRsprbv1ChtTTWAtf4Gs/sLtew=; b=EmoWHNnC3GmmT1fQR4b+eNyOdqxc4dSP/L7Ck/cPjz+laobHXJTPYrpx6RnpfnaYg6 jEMR+ZJHob86afxd2iTqe6yl770MccPz7Wh36Z4R4VrTdc+lLhVIEt5QhgGHfH3JKnMX LmIiCk/pzyCz5X/MBG+RRUZScnKlzLvV+MRsjaCSzrFr0TQHCz1s9Ukdrr7ysc4QXlWk 9HBbsfEeNsl+HQ8ISF5IrV2CxIGOXxjfH1iLOvlp8vR61axv/mmUt3fUvD06zF4Mfe2E aTV/Gun0pcpO9Bgwg+qfQEOQP/kVby/EzuJDx7Nlt22XEx74ouhjFFP/INIB86ECjh0Z OtZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=aihQYJyYU6rAhab/wfRsprbv1ChtTTWAtf4Gs/sLtew=; b=KBpJbzBFeBiy/VEQYNZbsL86nemx6dbZ5GSyHp/GJwhiu9ki21Sb2oJcn9Z1wlvqut 28wAAEjRR7x8pfzlrodaKMY7NAYrGACv2veeBNDiorsZ0/wx6geQ94BzC3w3Igu/hSQi A734OqDAftXZ491NAdcKlnvWCERfJ5pQbSQ0r0OInMfogH9rBp5CYWXmpceGfBmQbqcv sCauM4hU4om+ssFxzUEQEbYt29ciWMnP8+/v4ntIygEevndYoY5kWOuB7yWWYPYFHI8L qHV6RUoZhMvKEQJZYyA8TBv8J8dB6Q0tngNNFqezX7vsyYLxhw/RKfhrHDF1eFKWS4Uc /V4A== X-Gm-Message-State: ANhLgQ1HFKhcPynsRQQNiNu5BEP38wksMJUsVT/geYx0FGUu17LN7604 /8+O8IquReY6IILPypLTx4seXv/bGwGhcQ== X-Google-Smtp-Source: ADFU+vsS9GknTSE+3+5xm2leEa0Ul9szOKAXYY5z95L1JXYZd0kbMTU4A5zCU2nnGu8RBpDng5OejBWzi04V9w== X-Received: by 2002:a81:23d8:: with SMTP id j207mr1140477ywj.203.1583181081383; Mon, 02 Mar 2020 12:31:21 -0800 (PST) Date: Mon, 2 Mar 2020 12:31:09 -0800 Message-Id: <20200302203109.179417-1-shakeelb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.25.0.265.gbab2e86ba0-goog Subject: [PATCH v2] memcg: css_tryget_online cleanups From: Shakeel Butt To: Roman Gushchin Cc: Johannes Weiner , Michal Hocko , Andrew Morton , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Shakeel Butt Content-Type: text/plain; charset="UTF-8" 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: Currently multiple locations in memcg code, css_tryget_online() is being used. However it doesn't matter whether the cgroup is online for the callers. Online used to matter when we had reparenting on offlining and we needed a way to prevent new ones from showing up. The failure case for couple of these css_tryget_online usage is to fallback to root_mem_cgroup which kind of make bypassing the memcg limits possible for some workloads. For example creating an inotify group in a subcontainer and then deleting that container after moving the process to a different container will make all the event objects allocated for that group to the root_mem_cgroup. So, using css_tryget_online() is dangerous for such cases. Two locations still use the online version. The swapin of offlined memcg's pages and the memcg kmem cache creation. The kmem cache indeed needs the online version as the kernel does the reparenting of memcg kmem caches. For the swapin case, it has been left for later as the fallback is not really that concerning. Signed-off-by: Shakeel Butt --- Changes since v1: - replaced WARN_ON with WARN_ON_ONCE mm/memcontrol.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 62b574d0cd3c..75d8883bf975 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -656,7 +656,7 @@ __mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz) */ __mem_cgroup_remove_exceeded(mz, mctz); if (!soft_limit_excess(mz->memcg) || - !css_tryget_online(&mz->memcg->css)) + !css_tryget(&mz->memcg->css)) goto retry; done: return mz; @@ -961,7 +961,8 @@ struct mem_cgroup *get_mem_cgroup_from_page(struct page *page) return NULL; rcu_read_lock(); - if (!memcg || !css_tryget_online(&memcg->css)) + /* Page should not get uncharged and freed memcg under us. */ + if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css))) memcg = root_mem_cgroup; rcu_read_unlock(); return memcg; @@ -974,10 +975,13 @@ EXPORT_SYMBOL(get_mem_cgroup_from_page); static __always_inline struct mem_cgroup *get_mem_cgroup_from_current(void) { if (unlikely(current->active_memcg)) { - struct mem_cgroup *memcg = root_mem_cgroup; + struct mem_cgroup *memcg; rcu_read_lock(); - if (css_tryget_online(¤t->active_memcg->css)) + /* current->active_memcg must hold a ref. */ + if (WARN_ON_ONCE(!css_tryget(¤t->active_memcg->css))) + memcg = root_mem_cgroup; + else memcg = current->active_memcg; rcu_read_unlock(); return memcg; @@ -6732,7 +6736,7 @@ void mem_cgroup_sk_alloc(struct sock *sk) goto out; if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !memcg->tcpmem_active) goto out; - if (css_tryget_online(&memcg->css)) + if (css_tryget(&memcg->css)) sk->sk_memcg = memcg; out: rcu_read_unlock(); -- 2.25.0.265.gbab2e86ba0-goog