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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FROM,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 5059BC43387 for ; Sat, 22 Dec 2018 00:03:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 202E721928 for ; Sat, 22 Dec 2018 00:03:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="erpFjPWY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404232AbeLVADR (ORCPT ); Fri, 21 Dec 2018 19:03:17 -0500 Received: from mail-pl1-f193.google.com ([209.85.214.193]:38554 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727652AbeLVADN (ORCPT ); Fri, 21 Dec 2018 19:03:13 -0500 Received: by mail-pl1-f193.google.com with SMTP id e5so3167165plb.5; Fri, 21 Dec 2018 16:03:13 -0800 (PST) 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=RrGEExZrjErotvNk8wICdc9iWJu5BfH17QjMu1wcK58=; b=erpFjPWYBras5XE2h7nsoH4CdLPoGyR60K3sIf+/V/Z5Uhladw+3XWMK0w4rMo/YvW KP/AnoXHgbwBnie9tO3qa1j/diPkak4KdK7Sff3Yt2Exh5mYyVtCTsS1PAIdZuSckA2f FkPPIDRWISiC9fUvKALg71CR7ZW9amV1g+dmdceepd1EWlkuNpdCAC9b21MpxkMrRLkY H0nJHqJL7d12LixuISq7r/VjArt8BU+eRwgpHVVvDNlUnCiXOjGtwfeiIX8zRmQK++rE 6Ihu9hURk95nMuj2y04LzXKtG3GOK0BNoihZlkZxnOfEPtmlLAoz5Fs044P/05RDcrTR SPPA== 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=RrGEExZrjErotvNk8wICdc9iWJu5BfH17QjMu1wcK58=; b=kbAK7TFR1eYLDat9CDbAe9N2ydPza6GA8lDo+zbPI298udt/CLfhQIv8wsjcfiZScb xHPxurS/k3TLLhyjpQ9KJkZkt0h++esDDZF9oHXOcOohGnrzwR6v9qzwCW7Ww3f/r90t HH0/D7O+qw4PlyXbHzN76nzy+zHWsuW7K0rANPBD6oTkgmKqObLjOT43ZdVctCwjLwhT mArMAT07I9WAcSB1xyrpPB4tQ39K6MJFFgeVyHWfivh1DFfohyRmH9prle8zDr2jvJ5k YVUZzxoR2hJaCgn7DmemLrfPcTHedookwLmDpUushoUhA7gYEFZ73Gfk5cWwUJDPQ4ov iOmQ== X-Gm-Message-State: AJcUukfsbdgE+DYCO5hog1k1GUCTex67reRSvLqGgzdgaiBEGdDOBGW7 Cl5MMHrkl/I6TMHPrcChxDprJMuw5ZU= X-Google-Smtp-Source: ALg8bN75zWf4gjE6aEgez/C3w+4bl7LRi6ltSwGpaSLsgbNafexVJgCi/WxSOOlhamYDMBzcmLtxRA== X-Received: by 2002:a17:902:8e8b:: with SMTP id bg11mr4612870plb.332.1545436993195; Fri, 21 Dec 2018 16:03:13 -0800 (PST) Received: from tower.thefacebook.com ([2620:10d:c090:200::7:608f]) by smtp.gmail.com with ESMTPSA id 83sm36659266pgf.57.2018.12.21.16.03.12 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 21 Dec 2018 16:03:12 -0800 (PST) From: Roman Gushchin X-Google-Original-From: Roman Gushchin To: Tejun Heo , Oleg Nesterov Cc: kernel-team@fb.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Roman Gushchin Subject: [PATCH v6 3/7] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock Date: Fri, 21 Dec 2018 16:03:03 -0800 Message-Id: <20181222000307.28231-4-guro@fb.com> X-Mailer: git-send-email 2.19.2 In-Reply-To: <20181222000307.28231-1-guro@fb.com> References: <20181222000307.28231-1-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 8fcbae1b8db0..03355d7008ff 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 7519a4307021..f89dde50f693 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4723,9 +4723,11 @@ 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; @@ -4943,12 +4945,14 @@ 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); @@ -5233,10 +5237,12 @@ 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); -- 2.19.2