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Thu, 29 Oct 2026 18:04:34 +0000 (UTC) Received: from [100.91.18.181] (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 8E2941800643; Thu, 29 Oct 2026 18:04:32 +0000 (UTC) Message-ID: Date: Thu, 29 Oct 2026 14:04:31 -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-next] cgroup/cpuset: Fix incorrect CPU accounting with parent's effective_xcpus expansion To: Guopeng Zhang , Ridong Chen , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Shuah Khan Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20261028152608.648427-1-longman@redhat.com> <661486ab-4879-47cd-8035-ae0d7a7d7462@linux.dev> Content-Language: en-US From: Waiman Long In-Reply-To: <661486ab-4879-47cd-8035-ae0d7a7d7462@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On 10/29/26 5:42 AM, Guopeng Zhang wrote: > > 在 2026/10/28 23:26, Waiman Long 写道: >> Commit ec0254b9eb49 ("cgroup/cpuset: Release invalid isolated CPUs with >> a shrunk root partition parent") fixes incorrect isolated_cpus accounting >> when contraction of a parent's effective_xcpus can cause a child partition >> to lose isolated CPUs. Expansion of parent's effective_cpus can also allow >> a child partition to gain more effective_xcpus. However, the current code >> doesn't handle this case correctly leading to incorrect effective_cpus >> and isolated_cpus accounting. Fix that by looking for this possible >> expansion of effective_xcpus and perform the proper accounting action. >> >> New test cases are added to test this effective_xcpus expansion scenarios. >> >> Reported-by: Guopeng Zhang >> Link: https://lore.kernel.org/lkml/20261027123837.100909-1-guopeng.zhang@linux.dev >> Signed-off-by: Waiman Long > I have tested this patch. In the scenarios I tested, the double grant > and the isolated_cpus accounting after the expansion are now correct. > >> --- >> kernel/cgroup/cpuset.c | 12 ++++++++++++ >> tools/testing/selftests/cgroup/test_cpuset_prs.sh | 15 +++++++++++++++ >> 2 files changed, 27 insertions(+) >> >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >> index 3219f927c35e..39c81a0a8ab9 100644 >> --- a/kernel/cgroup/cpuset.c >> +++ b/kernel/cgroup/cpuset.c >> @@ -2097,6 +2097,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, >> parent->effective_xcpus); >> if (!cpumask_empty(tmp->addmask)) >> isolated_cpus_release(cs, tmp->addmask); >> + /* Expansion of parent's effective_xcpus is handled below */ >> } >> if (nocpu) { >> part_error = PERR_NOCPUS; >> @@ -2106,11 +2107,22 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, >> parent->effective_xcpus); >> } else if ((parent_prs == PRS_ISOLATED) && >> ((old_prs == PRS_ROOT) || (old_prs == -PRS_ROOT))) { >> + /* Parent partition state changed to PRS_ISOLATED */ >> part_error = PERR_ISOPARENT; >> if (old_prs == PRS_ROOT) { >> cpumask_copy(tmp->addmask, cs->effective_xcpus); >> adding = true; >> } >> + } else if (is_partition_valid(cs) && >> + !cpumask_equal(tmp->delmask, cs->effective_xcpus)) { > The branch is also entered when the freshly computed effective xcpus > shrink, e.g. after a parent contraction. The cpumask_andnot() then > computes an empty delta and it doesn't seem to cause any harm. Do we > need to tighten the condition? I intentionally made it simpler. For the shrink case, deleting will be false and nothing will be done. > >> + /* >> + * If there is an expansion of parent's effective_xcpus, >> + * we may take more xcpus from parent. The parent's >> + * effective_cpus should still have active CPUs or nocpu >> + * should have been set. >> + */ >> + deleting = cpumask_andnot(tmp->delmask, tmp->delmask, >> + cs->effective_xcpus); >> } else if (is_partition_invalid(cs)) { >> struct cgroup_subsys_state *css; >> struct cpuset *child; >> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh >> index 83ef6c781af3..844efdf029cd 100755 >> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh >> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh >> @@ -531,6 +531,21 @@ TEST_MATRIX=( >> " C1-4:P1 C3-4:P2 . . T:C4-6 . . . 0 A1:5-6|A2:4 A1:P1|A2:P2 4" >> " C1-4:P1 C1-2:P2 . . T:C4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ." >> >> + # The extra CPUs gained by a child partition when its parent expands the >> + # exclusive CPUs have to be taken away from the parent. >> + " C2-6:X2-5:P1 CX3-6:P1 \ >> + . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P1 ." >> + " C2-6:X2-5:P1 CX3-6:P2 \ >> + . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P2 3-6" >> + >> + # Both expansion and contraction of parent's effective_xcpus will be >> + # correctly handled in child partition and the child can be invalidated >> + # if a populated parent could lose all its effective_cpus. >> + " C2-6:X2-5:P1 CX3,5-6:P2 \ >> + . . X4-6 . . . 0 A1:4|A2:5-6|XA2:5-6 A1:P1|A2:P2 5-6" >> + " C2-6:X2-5:P1 CX3-6:P2 \ >> + . . T:X4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ." >> + >> # >> # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS >> # ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ -------- > BTW, about the housekeeping check issue from my previous email. > I verified it with the session below on a nohz_full=8-31 boot where > CPUs 0-7 are the housekeeping CPUs: > > # cat /sys/devices/system/cpu/nohz_full > 8-31 > # cd /sys/fs/cgroup > # echo +cpuset > cgroup.subtree_control > # mkdir -p A/B > # echo 0-7 > A/cpuset.cpus > # echo 1-7 > A/cpuset.cpus.exclusive > # echo root > A/cpuset.cpus.partition > # echo +cpuset > A/cgroup.subtree_control > # echo 0-7 > A/B/cpuset.cpus > # echo 0-7 > A/B/cpuset.cpus.exclusive > # echo isolated > A/B/cpuset.cpus.partition > # cat /sys/fs/cgroup/cpuset.cpus.isolated > 1-7 > # cat A/B/cpuset.cpus.exclusive.effective > 1-7 > # echo 0-7 > A/cpuset.cpus.exclusive > # cat A/B/cpuset.cpus.partition > isolated > # cat /sys/fs/cgroup/cpuset.cpus.isolated > 0-7 > > B stays a valid isolated partition holding all the housekeeping CPUs > and there is no warning at all. > > If the housekeeping issue is going to be addressed in this series, is > a test case like the one below worth adding? > > + # An isolated child partition cannot grow to take over the last > + # housekeeping CPU when its parent expands the exclusive CPUs. > + " C0-7:X1-7:P1 C0-7:X0-7:P2 . . X0-7 . . . 0 A1:0-7 A1:P1|A2:P-2 ." > > I will fix that with another patch. Cheers, Longman