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=-8.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 56665C43381 for ; Sat, 16 Mar 2019 17:58:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2ECF3218D4 for ; Sat, 16 Mar 2019 17:58:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="gwzhwtuY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727238AbfCPR60 (ORCPT ); Sat, 16 Mar 2019 13:58:26 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:33457 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727216AbfCPR6W (ORCPT ); Sat, 16 Mar 2019 13:58:22 -0400 Received: by mail-pg1-f195.google.com with SMTP id i7so5383621pgq.0; Sat, 16 Mar 2019 10:58:22 -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 :mime-version:content-transfer-encoding; bh=pSVREjPCAv5T2ZXAYt7SDw0JOGFlD724donHrtDZGs4=; b=gwzhwtuYHAukJnuCVE538uazrdK6lMvAnBOSu2ZJL8T/RzBz73VGy9TYw3ELDMkriz H0EdPTa4z4G9HOheuqpLS9KnS2TIpPVE1kkiRHGj3R72fZtBoeEH+JIRVpXAxlP13Uzy zngGXAzT5DCbVbalF12VD3qtnkCYBIrxtUbAh458w5jkQd4xqtzOhGgENrUCdZUKesTb G8tF8PHci7Ec+yjdVYVJ0KkvYJlWssDi4h31/R/1pyLF+2KZ5p4KZAvFJ+IaAz6bvP8J WAImBgK1fhFSRakIcxykVU5d2K2W2aZ9HdASO6Wso+25ayUerc9YcNu4dh6eyVTyMKjl TsWw== 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:mime-version:content-transfer-encoding; bh=pSVREjPCAv5T2ZXAYt7SDw0JOGFlD724donHrtDZGs4=; b=tN24490vxtu3VYUAGyk/D9mDC6UBfostIoL+cmuA+HhHylW7MxJlbaIFs+iGwduTAa QHcoDojbXu9S/tNQ+wP/OtJkFtFPw1LNRD4b9i2U26vcBG33x4g2lx3y7h4EvSPsnJ+G KX9QeG65XT7htPU3/cDZe5x/Krc8KIeSvLhuQ081Y/BMUczp1P8GBJy3IcnvLtEZPA08 SrmcxYQFGU99qLVJVbQIJYpmK30qfKSqCvZTj14DjTxS9i2US2SnP+evV1MAmZ2b4giy U2J1LVA4u/D6PfGNDcnfLRevKutym7r4/7Qwvn7Y+xy6Y4n72c98reWB3pPYVABiswe6 2YjA== X-Gm-Message-State: APjAAAVJyHnIvgouFz6A9eBC0OumoWZi3mmhDFEXUt/mn1Hfea8B1DC9 a79kjVy2RPhwz7/VJHWebWCaneKOtE4= X-Google-Smtp-Source: APXvYqwyoU76a5n+PfJG348JHEdw7Xmgs5gVM7mVfGcMTT6wwac3J9QT/VZQ++KrtxMLrB5dPc2sZw== X-Received: by 2002:a17:902:10d:: with SMTP id 13mr3058421plb.230.1552759102246; Sat, 16 Mar 2019 10:58:22 -0700 (PDT) Received: from castle.hsd1.ca.comcast.net ([2603:3024:1704:3e00::d657]) by smtp.gmail.com with ESMTPSA id p86sm11025638pfa.104.2019.03.16.10.58.20 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 16 Mar 2019 10:58:20 -0700 (PDT) From: Roman Gushchin X-Google-Original-From: Roman Gushchin To: Tejun Heo , Oleg Nesterov Cc: Roman Gushchin , kernel-team@fb.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v9 3/9] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock Date: Sat, 16 Mar 2019 10:58:06 -0700 Message-Id: <20190316175812.6787-4-guro@fb.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190316175812.6787-1-guro@fb.com> References: <20190316175812.6787-1-guro@fb.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The number of descendant cgroups and the number of dying descendant cgroups are currently synchronized using the cgroup_mutex. The number of descendant cgroups will be required by the cgroup v2 freezer, which will use it to determine if a cgroup is frozen (depending on total number of descendants and number of frozen descendants). It's not always acceptable to grab the cgroup_mutex, especially from quite hot paths (e.g. exit()). To avoid this, let's additionally synchronize these counters using the css_set_lock. So, it's safe to read these counters with either cgroup_mutex or css_set_lock locked, and for changing both locks should be acquired. Signed-off-by: Roman Gushchin Cc: Tejun Heo Cc: kernel-team@fb.com --- include/linux/cgroup-defs.h | 5 +++++ kernel/cgroup/cgroup.c | 6 ++++++ 2 files changed, 11 insertions(+) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 120d1d40704b..319c07305500 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -348,6 +348,11 @@ struct cgroup { * Dying cgroups are cgroups which were deleted by a user, * but are still existing because someone else is holding a reference. * max_descendants is a maximum allowed number of descent cgroups. + * + * nr_descendants and nr_dying_descendants are protected + * by cgroup_mutex and css_set_lock. It's fine to read them holding + * any of cgroup_mutex and css_set_lock; for writing both locks + * should be held. */ int nr_descendants; int nr_dying_descendants; diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index b230afccf635..7438c24297d4 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4758,9 +4758,11 @@ static void css_release_work_fn(struct work_struct *work) if (cgroup_on_dfl(cgrp)) cgroup_rstat_flush(cgrp); + spin_lock_irq(&css_set_lock); for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) tcgrp->nr_dying_descendants--; + spin_unlock_irq(&css_set_lock); cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id); cgrp->id = -1; @@ -4978,12 +4980,14 @@ static struct cgroup *cgroup_create(struct cgroup *parent) if (ret) goto out_psi_free; + spin_lock_irq(&css_set_lock); for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) { cgrp->ancestor_ids[tcgrp->level] = tcgrp->id; if (tcgrp != cgrp) tcgrp->nr_descendants++; } + spin_unlock_irq(&css_set_lock); if (notify_on_release(parent)) set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); @@ -5268,10 +5272,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) if (parent && cgroup_is_threaded(cgrp)) parent->nr_threaded_children--; + spin_lock_irq(&css_set_lock); for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) { tcgrp->nr_descendants--; tcgrp->nr_dying_descendants++; } + spin_unlock_irq(&css_set_lock); cgroup1_check_for_release(parent); -- 2.20.1