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Thu, 22 Oct 2026 03:31:16 +0000 (UTC) Received: from [100.91.18.181] (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id CE3EF433; Thu, 22 Oct 2026 03:31:14 +0000 (UTC) Message-ID: <71bc8d63-456c-4dcb-9d03-c2881f41af78@redhat.com> Date: Wed, 21 Oct 2026 23:31:14 -0400 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] cgroup/cpuset: Fix partition recovery with unavailable CPUs To: Guopeng Zhang , tj@kernel.org Cc: ridong.chen@linux.dev, hannes@cmpxchg.org, mkoutny@suse.com, shuah@kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Guopeng Zhang References: <20261020133315.123890-1-guopeng.zhang@linux.dev> Content-Language: en-US From: Waiman Long In-Reply-To: <20261020133315.123890-1-guopeng.zhang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 On 10/20/26 9:33 AM, Guopeng Zhang wrote: > From: Guopeng Zhang > > An invalid local partition can become valid again even when its > exclusive CPUs are no longer available from its parent. > > This can be reproduced on a cgroup v2 system with CPUs 0-7 online: > > cd /sys/fs/cgroup > echo +cpuset > cgroup.subtree_control > mkdir A > echo 1-4 > A/cpuset.cpus > echo 1-4 > A/cpuset.cpus.exclusive > echo root > A/cpuset.cpus.partition > echo +cpuset > A/cgroup.subtree_control > mkdir A/B > echo 3-4 > A/B/cpuset.cpus > echo 3-4 > A/B/cpuset.cpus.exclusive > echo root > A/B/cpuset.cpus.partition > echo 1-2 > A/cpuset.cpus.exclusive > cat A/B/cpuset.cpus.partition > root > cat A/B/cpuset.cpus.exclusive.effective > cat A/cpuset.cpus.effective > 1-2 > cat A/B/cpuset.cpus.effective > 1-2 > > B is changed back to a valid root even though its exclusive CPUs are > no longer available and cpuset.cpus.exclusive.effective is empty. B > should remain invalid until A can provide its exclusive CPUs again. > > Shrinking A's exclusive CPUs invalidates B in > compute_partition_effective_cpumask(). The subsequent walk in > update_cpumasks_hier() tries to recover B, but > update_parent_effective_cpumask() skips the recovery checks when xcpus > is not a subset of parent->effective_xcpus. Since part_error is still > zero, B is changed back to a valid partition. > > Set PERR_INVCPUS when the subset check fails so that the partition stays > invalid. New test cases are added to test_cpuset_prs.sh for removing and > restoring the parent's exclusive CPUs. > > Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2") > Signed-off-by: Guopeng Zhang > --- > kernel/cgroup/cpuset.c | 8 ++++++-- > tools/testing/selftests/cgroup/test_cpuset_prs.sh | 4 ++++ > 2 files changed, 10 insertions(+), 2 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 585a982249ad..be80763953ed 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1986,12 +1986,16 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, > cpumask_copy(tmp->addmask, cs->effective_xcpus); > adding = true; > } > - } else if (is_partition_invalid(cs) && !cpumask_empty(xcpus) && > - cpumask_subset(xcpus, parent->effective_xcpus)) { > + } else if (is_partition_invalid(cs) && !cpumask_empty(xcpus)) { > struct cgroup_subsys_state *css; > struct cpuset *child; > bool exclusive = true; > > + if (!cpumask_subset(xcpus, parent->effective_xcpus)) { > + part_error = PERR_INVCPUS; > + goto write_error; > + } > + > /* > * Convert invalid partition to valid has to pass the > * cpu exclusivity test as well as the housekeeping > diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh > index d04aad697b96..f1d517647ade 100755 > --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh > +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh > @@ -427,6 +427,10 @@ TEST_MATRIX=( > # cpuset.cpus is allowed, but those extra CPUs are ignored. > " C2-3:P1 C3:P1 . . . C2-4 . . 0 A1:|A2:2-3 A1:P1|A2:P1" > > + # A child cannot recover until its exclusive CPUs are available again. > + " CX1-4:P1 CX3-4:P1 . . X1-2 . . . 0 A1:1-2|A2:1-2|XA2: A1:P1|A2:P-1" > + " CX1-4:P1 CX3-4:P1 . . X1-2:X1-4 . . . 0 A1:1-2|A2:3-4|XA2:3-4 A1:P1|A2:P1" > + > # Taking away all CPUs from parent or itself if there are tasks > # will make the partition invalid. > " C2-3:P1 C3:P1 . . T C2-3 . . 0 A1:2-3|A2:2-3 A1:P1|A2:P-1" Patch 2 of my series should fix this problem too. I do borrow your test cases in my patch. I hope you don't mind about it. Cheers, Longman