From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 7564A541E44 for ; Wed, 14 Oct 2026 14:06:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791986798; cv=none; b=sUKSt28kVucFEAfeODHlokEINmdmo9SrNrDUnF+VEFi6K8rEecGl7Unz6ZDDFoNAnQX77j09sZ0tu1H9gykeqVfNC5zr04lwTxRjFD/3ygIL3r7Y+YEmeriziHGJCPoBcJrCUh2MsnCasrtnGFlJePqZdIG8IDk6iwK9LqIfFXY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791986798; c=relaxed/simple; bh=1S6V3BBmV/FRBQZzigWlCu+O7+/Gj7IFuk0w6N/11FY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=gpmrEUDbj3Z0+/oWJTqd5Ka3kQIiQfo7urwqU3RMz/Jfqt+sDDpENpPBO103kM/JWUgvSUNgnP2ZoQgQv8IOocDUQPoOOvd8vIIUg2hbILEBOMgUYb4Od9O3NBLS/KEwSLQz8a5n+/kT7Qkrn1VYIGL69NRYTU7RB5ti9jLjdjU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ZJ5pB5lE; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZJ5pB5lE" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791986787; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9wGU+yhb3bVje6hDfkLGUe+XAk9XLTdvAsG9YvpbpH4=; b=ZJ5pB5lEMHglieosogmUo0T5PXC6hFFYZ3/sPI+moXhiDRBoQGGqI4B4zsAxZjIDo0oxFU FnJn1cdiYv21d3RIREj2PGgsVGh2jken1xXjVHnjNTYCRQhzI3z5FvrGoDuJsVq5Ak+7jt B1/CQWjHRDJvnPgiLybX5sGCMTjlMPU= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-355-NwWOrrnEN5OMaDF-hulfig-1; Wed, 14 Oct 2026 14:06:23 +0000 X-MC-Unique: NwWOrrnEN5OMaDF-hulfig-1 X-Mimecast-MFC-AGG-ID: NwWOrrnEN5OMaDF-hulfig_1791986780 Received: from mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.95]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A85931800772; Wed, 14 Oct 2026 14:06:20 +0000 (UTC) Received: from llong-thinkpadp16vgen1.rmtusnh.csb (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id AD62C418; Wed, 14 Oct 2026 14:06:18 +0000 (UTC) From: Waiman Long To: Ridong Chen , Tejun Heo , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Shuah Khan , Jonathan Corbet , Randy Dunlap Cc: cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Hui Peng , Guopeng Zhang , Waiman Long Subject: [PATCH-next v3 6/9] cgroup/cpuset: Don't allow a child root partition under an isolated parent Date: Wed, 14 Oct 2026 10:05:45 -0400 Message-ID: <20261014140548.575122-7-longman@redhat.com> In-Reply-To: <20261014140548.575122-1-longman@redhat.com> References: <20261014140548.575122-1-longman@redhat.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 Although it is not typical for real users to create a complicated nested partition hierarchy, it is currently allowed to create nested root and isolated partitions. In addition, disabling or invalidating a partition should always be allowed especially when the cpuset is being deleted. With a nested root and isolated partition hierarchy, it is possible that all active housekeeping CPUs can be exhausted when disabling or invalidating a root partition and returning its CPUs to the isolated parent. One way to avoid this problem is to disallow the creation of a root partition under an isolated parent. It is indeed a new limitation imposed on the existing cpuset partition functionality. However an isolated partition is usually a left node where scheduling and some other kernel noises are disabled. It doesn't make much sense to create a child root partition under an isolated parent and remove some CPUs from the set of isolated CPUs again. Creation of a child isolated partition under a root or isolated parent is still allowed. The cgroup-v2 documentation is also updated to reflect this new limitation. New test cases are added to test_cpuset_prs.sh to verify this new behavior. Some existing test cases are also updated accordingly. Signed-off-by: Waiman Long --- Documentation/admin-guide/cgroup-v2.rst | 4 +++- kernel/cgroup/cpuset-internal.h | 1 + kernel/cgroup/cpuset.c | 13 +++++++++++++ tools/testing/selftests/cgroup/test_cpuset_prs.sh | 14 ++++++++------ 4 files changed, 25 insertions(+), 7 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index bd8c80f3bbc9..2c445829e24d 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2767,7 +2767,9 @@ Cpuset Interface Files be retained, but behaves more like a "member". All possible state transitions among "member", "root" and - "isolated" are allowed. + "isolated" are allowed with the exception that a local child + "root" partition is not allowed to be created under an "isolated" + parent partition. On read, the "cpuset.cpus.partition" file can show the following values. diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h index 5da9c91295b0..2e44dc8634dc 100644 --- a/kernel/cgroup/cpuset-internal.h +++ b/kernel/cgroup/cpuset-internal.h @@ -35,6 +35,7 @@ enum prs_errcode { PERR_HKEEPING, PERR_ACCESS, PERR_REMOTE, + PERR_ISOPARENT, }; /* bits in struct cpuset flags field */ diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 40c004386af0..681701ba46e1 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -60,6 +60,7 @@ static const char * const perr_strings[] = { [PERR_HKEEPING] = "partition config conflicts with housekeeping setup", [PERR_ACCESS] = "Enable partition not permitted", [PERR_REMOTE] = "Have remote partition underneath", + [PERR_ISOPARENT] = "Root partition is not allowed with isolated parent", }; /* @@ -2865,6 +2866,7 @@ static int update_prstate(struct cpuset *cs, int new_prs) int err = PERR_NONE, old_prs = cs->partition_root_state; struct cpuset *parent = parent_cs(cs); struct tmpmasks tmpmask; + int parent_prs = parent->partition_root_state; bool isolcpus_updated = false; bool disable_partition = false; @@ -2910,6 +2912,14 @@ static int update_prstate(struct cpuset *cs, int new_prs) enum partition_cmd cmd = (new_prs == PRS_ROOT) ? partcmd_enable : partcmd_enablei; + /* + * It is not allowed to create a root partition under + * an isolated parent partition. + */ + if ((new_prs == PRS_ROOT) && (parent_prs == PRS_ISOLATED)) { + err = PERR_ISOPARENT; + goto out; + } err = update_parent_effective_cpumask(cs, cmd, NULL, &tmpmask); } else { err = remote_partition_enable(cs, new_prs, &tmpmask); @@ -2922,6 +2932,9 @@ static int update_prstate(struct cpuset *cs, int new_prs) if (prstate_housekeeping_conflict(new_prs, cs->effective_xcpus)) { disable_partition = true; err = PERR_HKEEPING; + } else if (parent_prs == PRS_ISOLATED) { + disable_partition = true; + err = PERR_ISOPARENT; } else { isolcpus_updated = true; } diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh index 874a8a161236..85a4f87840b4 100755 --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh @@ -288,16 +288,12 @@ TEST_MATRIX=( A1:P0|A2:P1|A3:P0|B1:P1" " C0-3 C1-3 C3 C4 X2-3 X2-3:P1 P2 P1 0 A1:0-1|A2:2|A3:3|B1:4 \ A1:P0|A2:P1|A3:P2|B1:P1 2-4|3" - " C0-4 C1-4 C2-4 . X2-4 X2-4:P2 X4:P1 . 0 A1:0-1|A2:2-3|A3:4 \ - A1:P0|A2:P2|A3:P1 2-4|2-3" - " C0-4 C1-4 C2-4 . X2-4 X2-4:P2 X3-4:P1 . 0 A1:0-1|A2:2|A3:3-4 \ - A1:P0|A2:P2|A3:P1 2" " C0-4:X2-4 C1-4:X2-4:P1 C2-4:X4:P2 \ . . X5 . . 0 A1:0-4|A2:1-4|A3:2-4 \ A1:P0|A2:P-1|A3:P-2 ." - " C0-4:X2-4 C1-4:X2-4:P2 C2-4:X4:P1 \ + " C0-4:X2-4 C1-4:X2-4:P1 C2-4:X4:P2 \ . . . X1 . 0 A1:0-1|A2:2-4|A3:2-4 \ - A1:P0|A2:P2|A3:P-1 2-4" + A1:P0|A2:P1|A3:P-2 ." " CX1-3:P1 CX1-3 CX1-3 . . . P1 . 0 A1:1-3|A2:1-3|A3:1-3 \ A1:P1|A2:P0|A3:P-1" @@ -430,6 +426,12 @@ TEST_MATRIX=( # cpuset.cpus can become empty with task in it as it inherits parent's effective CPUs " C1-3 C2 . . . T:C . . 0 A1:1-3|A2:1-3" + # Creation of root partition under an isolated partition is not allowed + " C1-3:P2 C2 . . . P1 . . 0 A1:1-3|A2:2 A1:P2|A2:P-1 1-3" + " C1-3:P2 C2 . . . P2 . . 0 A1:1,3|A2:2 A1:P2|A2:P2 1-3" + " C1-3:P2 C2:P2 . . . P1 . . 0 A1:1-3|A2:2 A1:P2|A2:P-1 1-3" + + # # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS # ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ -------- # Failure cases: -- 2.55.0