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 4050BC282DA for ; Fri, 5 Apr 2019 17:47:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 10B382171F for ; Fri, 5 Apr 2019 17:47:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="J68x9X82" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731707AbfDERrm (ORCPT ); Fri, 5 Apr 2019 13:47:42 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:35505 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731633AbfDERrf (ORCPT ); Fri, 5 Apr 2019 13:47:35 -0400 Received: by mail-pl1-f196.google.com with SMTP id w24so3421760plp.2; Fri, 05 Apr 2019 10:47:35 -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=lZLLa5MWCUzqpcbdhGYUwTVi7fb5Sf8gELlrzCcLpf8=; b=J68x9X8233cAedrO+T1UTwAbjYnCXXKepQg4YtENX2bg4PkeJLifgfDthmv7qWl0ol Nf+yUiPOUY8cY9kyGlMUpmXISI8hlwvtX7ZzPie6ZPS1EBaQoeyZkKIbFjRbONw3GAK4 M8P/efLJMrNl+2OxFfiNcT89/9LpUEnMoGi9nCIafg0WYn+117Q3MZOgF1oVXvGo+HQb GXFK6cqXeTOIIr1ew2Gz7EDLYeQurHUDXOOddop4nE+rUDjmRqDwTnQr33yJqoQ+jqtn UiKVBZ6hKrJIFUdCmDBt9K+505Kg4PTGKlheMgCjoL84wVHnt2d8HULQdc2kiE3NiSQH DEXw== 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=lZLLa5MWCUzqpcbdhGYUwTVi7fb5Sf8gELlrzCcLpf8=; b=dMdIf8g9pQgZ95CgT3tgRhsgjRBNn9k417Io5xtO/Rcj8lnH12gy7pq6pWGxQ/TFgz oBOLXYcSKznui0tS4WK6MYvLygxG0f0LxaP0ULQNlnu6NszBSd8L9WKW0j8l5MfmSYmx WCyb6dxBVCguQaNKygxI7fuX7UxeHXlEk/Ql57hF4QCBLqKiasO/J67YBJdVzG4O4O36 ceA8jcFS5/HPJYP96BumLGJo1y9f7r297g8O/OsoQ851v5sLAbhGYFUVUvXjoBFmpWB5 mlaGHjokK5wJc+KdiKaf+1AlCGHs1xp7ESFExnkpDbMCPqCIiYIM/d4U1N5/dgMPo9pi mNBQ== X-Gm-Message-State: APjAAAVBZNBDjju5iH9uhoujxHbJ/x5uIUMaTF4T+vAPbv5Jfi/OEG2C fYLigt7p3GhdEEVGhjAlW/w= X-Google-Smtp-Source: APXvYqw1PHeb2x+LhHs1rM+BO8feGC1jGw5/37ksWOp+FQFRYAPse1e+IHMZlO2lZRDXO4J/AZDvCw== X-Received: by 2002:a17:902:362:: with SMTP id 89mr14485867pld.172.1554486455005; Fri, 05 Apr 2019 10:47:35 -0700 (PDT) Received: from tower.thefacebook.com ([2620:10d:c090:200::1:ad20]) by smtp.gmail.com with ESMTPSA id m2sm33169135pgr.74.2019.04.05.10.47.33 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 05 Apr 2019 10:47:34 -0700 (PDT) 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 v10 3/9] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock Date: Fri, 5 Apr 2019 10:47:02 -0700 Message-Id: <20190405174708.1010-4-guro@fb.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190405174708.1010-1-guro@fb.com> References: <20190405174708.1010-1-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 1c70803e9f77..7d57890cec67 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -349,6 +349,11 @@ 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 3008ea684aa0..786ceef2f222 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4811,9 +4811,11 @@ 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; @@ -5031,12 +5033,14 @@ 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); @@ -5321,10 +5325,12 @@ 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