From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3BF173BE175; Sat, 12 Sep 2026 07:08:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789196898; cv=none; b=Pi3L0ZL1LKdvyuLOKbjnOJe+b3OI/UvD2ACdoVaeiH2FTY4Y/3aQ010vARchCslsXN3H6Kead1iA+mWZghgoIKNiM/3Y9P+Wyb0jB7+BDDXwgfFe/QHfTY0cB+a/PUgooSsfjBHN/Aeb2gNHbIvRA9h0EdEHA6IWoU86lJUIfiA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789196898; c=relaxed/simple; bh=9plSxbzIR9/y5Z7pLr51EjskLMOfEP/EW8p8ge76UU8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YNiPG+v8KAKbt4tMbPqgQORjK9bnOKZh48wGEFAlFcgksV5pW4oNINSACq0XEVSaP33CqfE4RC6GWC6qIWztsVr63fKtws1/Q+9LLIsTVsBektGV6iMKKbkYLzNppqJN0VeYbj/mUhxZjmmzsQB1RyocYRIay2dJL68mKoI+wUk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zx4svdiz; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="zx4svdiz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C5CFC1F000FF; Sat, 12 Sep 2026 07:08:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789196896; bh=o771KH/07E5TIwKs+lEbg1C2Iw0PKV9EWFnNeWWsXZI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=zx4svdizLZULL7ozpTY15EiKWTVmzXX4ZeW1GLZGVeu3ad72M21hDUHTl4X9jygXt QNRP1hx72pUgZYI6KLhn3qmPzQD/JbBEAJedcbjHkXLHAhK2/5bzgaqMSGp17U60VR 5x1NJAt+dfzPRico/dzyDz+RnOStTpquIJDLLmgQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ridong Chen , Waiman Long , Tejun Heo , Sasha Levin Subject: [PATCH 7.2 0060/1815] cgroup/cpuset: Avoid unnecessary cpus & mems update in cpuset_hotplug_update_tasks() Date: Sat, 12 Sep 2026 08:30:10 +0200 Message-ID: <20260912065650.421726085@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065648.999753832@linuxfoundation.org> References: <20260912065648.999753832@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Waiman Long [ Upstream commit 866f587e9c70566a0391bf402123555605a82f81 ] As reported by sashiko [1], cpuset_hotplug_update_tasks() may perform unnecessary task iteration and updating of tasks' CPU and node masks when mems_allowed and/or cpus_allowed are not set in cpuset v2. It is due to the fact that the temporary new_cpus and new_mems masks do not inherit parent's effective_cpus/mems when they are empty which is the expected behavior for cpuset v2 since commit 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy"). Fix that and avoid unnecessary work by enhancing compute_effective_cpumask() to add the empty cpumask check and inheriting the parent's versions if empty when in v2. A new compute_effective_nodemask() helper is also added to perform a similar function for new effective_mems. Add new test_cpuset_prs.sh test cases to confirm that effective_cpus will inherit the parent's version if cpuset.cpus is empty. [1] https://sashiko.dev/#/patchset/20260621032816.1806773-1-longman%40redhat.com Suggested-by: Ridong Chen Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy") Signed-off-by: Waiman Long Reviewed-by: Ridong Chen Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- kernel/cgroup/cpuset.c | 45 +++++++++++-------- .../selftests/cgroup/test_cpuset_prs.sh | 11 ++++- 2 files changed, 35 insertions(+), 21 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 45944b3e31ca4..cce1f0e292ade 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1089,12 +1089,35 @@ void cpuset_update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus) * @cs: the cpuset the need to recompute the new effective_cpus mask * @parent: the parent cpuset * + * For v2, the parent's effective_cpus is inherited if cpumask is empty. * The result is valid only if the given cpuset isn't a partition root. */ static void compute_effective_cpumask(struct cpumask *new_cpus, struct cpuset *cs, struct cpuset *parent) { - cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus); + bool has_cpus; + + has_cpus = cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus); + if (!has_cpus && is_in_v2_mode()) + cpumask_copy(new_cpus, parent->effective_cpus); +} + +/** + * compute_effective_nodemask - Compute the effective nodemask of the cpuset + * @new_mems: the temp variable for the new effective_mems mask + * @cs: the cpuset the need to recompute the new effective_mems mask + * @parent: the parent cpuset + * + * For v2, the parent's effective_mems is inherited if nodemask is empty. + */ +static void compute_effective_nodemask(nodemask_t *new_mems, + struct cpuset *cs, struct cpuset *parent) +{ + bool has_mems; + + has_mems = nodes_and(*new_mems, cs->mems_allowed, parent->effective_mems); + if (!has_mems && is_in_v2_mode()) + nodes_copy(*new_mems, parent->effective_mems); } /* @@ -2143,15 +2166,6 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, goto update_parent_effective; } - /* - * If it becomes empty, inherit the effective mask of the - * parent, which is guaranteed to have some CPUs unless - * it is a partition root that has explicitly distributed - * out all its CPUs. - */ - if (is_in_v2_mode() && !remote && cpumask_empty(tmp->new_cpus)) - cpumask_copy(tmp->new_cpus, parent->effective_cpus); - /* * Skip the whole subtree if * 1) the cpumask remains the same, @@ -2697,14 +2711,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems) cpuset_for_each_descendant_pre(cp, pos_css, cs) { struct cpuset *parent = parent_cs(cp); - bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems); - - /* - * If it becomes empty, inherit the effective mask of the - * parent, which is guaranteed to have some MEMs. - */ - if (is_in_v2_mode() && !has_mems) - *new_mems = parent->effective_mems; + compute_effective_nodemask(new_mems, cp, parent); /* Skip the whole subtree if the nodemask remains the same. */ if (nodes_equal(*new_mems, cp->effective_mems)) { @@ -3778,7 +3785,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) parent = parent_cs(cs); compute_effective_cpumask(&new_cpus, cs, parent); - nodes_and(new_mems, cs->mems_allowed, parent->effective_mems); + compute_effective_nodemask(&new_mems, cs, parent); if (!tmp || !cs->partition_root_state) goto update_tasks; diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh index 0d41aa0d343d9..ca9bc38fdb95d 100755 --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh @@ -495,13 +495,20 @@ REMOTE_TEST_MATRIX=( # Narrowing cpuset.cpus to previously sibling-excluded CPUs should # not return CPUs that were never actually owned. " C1-4:P1 . C1-2:P1 C1-3:P2 . . \ - . . . C3 . . p1:4|c11:1-2|c12:3 \ + . . . C3 . . p1:4|c11:1-2|c12:3 \ p1:P1|c11:P1|c12:P2 3" # Expanding cpuset.cpus to include a previously sibling-excluded CPU # after the sibling has become a member should correctly request it. " C1-4:P1 . C1-2:P1 C1-3:P2 . . \ - . . P0 C2-3 . . p1:1,4|c11:1|c12:2-3 \ + . . P0 C2-3 . . p1:1,4|c11:1|c12:2-3 \ p1:P1|c11:P0|c12:P2 2-3" + # Cpusets with empty cpuset.cpus should inherit parent's effective_cpus + " C1-4:P1 C5-6 C1-2 . C5 . \ + . P1 P1 . . . p1:3-4|p2:5-6|c11:1-2|c12:3-4|c21:5|c22:5-6 \ + p1:P1|p2:P1|c11:P1" + " C1-4:P1 C5-6 C1-2 . C5 . \ + . P1 P1 . O5=0 . p1:3-4|p2:6|c11:1-2|c12:3-4|c21:6|c22:6 \ + p1:P1|p2:P1|c11:P1" ) # -- 2.53.0