From nobody Mon Feb 9 09:10:19 2026 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 AE1CB277C9D for ; Mon, 3 Nov 2025 01:34:50 +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=1762133692; cv=none; b=uEl+aza316zsIjm/O4kYhujtsR96zzpzQ93yqSBVWvLl1akqKVzJXDGa3wCYp2dCb5unKcnLAgDPa8Jg1O4xbDVkhQOH6cORkS9gE/48qqEwgdtgFhpwG9jzsXd4abwoKhriAklgR9r1mR8gHEqyeLyv7HCgfmx53Fv4LaihASA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762133692; c=relaxed/simple; bh=QSMtuZJlhpfZlw9xjWM2VWoOgLqSemwPU5bvVsW8OIw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Kebcwdrf/ua+2nUObDAsxSDZU8E0/orHs2JQrQPNr9hrOCMTp1xzPtF0AZoTTUHMJ1NyftHIMtaijtf5f+caTSga8xlpHtdjYcOj1tE7Ats4O8kcglyyffAuVqjnIsEkYlajBvqH/rS6DBlzHgUVuITtnhUYUD88VbLvmB4io4Q= 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=grFOhqaL; 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="grFOhqaL" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1762133689; 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=wHTWsmFtq1a6G99r8MhP4nYSCSSdkZKXE/3thNe7Rmg=; b=grFOhqaL8qKWaHWf4Zk5jYq9N/cT+OkEi5j4v6GuO0zrzV2g4Vw5XfHUkC0a7+vPmyLY5s ATvaDXE14SHyNP3d4o3ZzbyrqIJIh7ZVSfyVqZ5WYMzHbAI7KRnBrLkWHOxplB7FRvIXUQ ++tfW/+szdu0/PUja4FoSicSAMnzP3U= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-613-0dqW8CewORCsdZfIpKMGUA-1; Sun, 02 Nov 2025 20:34:46 -0500 X-MC-Unique: 0dqW8CewORCsdZfIpKMGUA-1 X-Mimecast-MFC-AGG-ID: 0dqW8CewORCsdZfIpKMGUA_1762133685 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 48B241956066; Mon, 3 Nov 2025 01:34:45 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.88.7]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 695B71956056; Mon, 3 Nov 2025 01:34:43 +0000 (UTC) From: Waiman Long To: Tejun Heo , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Chen Ridong , Gabriele Monaco , Frederic Weisbecker , Waiman Long Subject: [cgroup/for-6.19 PATCH 2/3] cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping Date: Sun, 2 Nov 2025 20:34:10 -0500 Message-ID: <20251103013411.239610-3-longman@redhat.com> In-Reply-To: <20251103013411.239610-1-longman@redhat.com> References: <20251103013411.239610-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Content-Type: text/plain; charset="utf-8" From: Gabriele Monaco Currently the user can set up isolated cpus via cpuset and nohz_full in such a way that leaves no housekeeping CPU (i.e. no CPU that is neither domain isolated nor nohz full). This can be a problem for other subsystems (e.g. the timer wheel imgration). Prevent this configuration by blocking any assignation that would cause the union of domain isolated cpus and nohz_full to covers all CPUs. Acked-by: Frederic Weisbecker Reviewed-by: Waiman Long Signed-off-by: Gabriele Monaco Signed-off-by: Waiman Long --- kernel/cgroup/cpuset.c | 67 +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 66 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index da770dac955e..d6d459c95d82 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1329,6 +1329,19 @@ static void isolated_cpus_update(int old_prs, int ne= w_prs, struct cpumask *xcpus cpumask_andnot(isolated_cpus, isolated_cpus, xcpus); } =20 +/* + * isolated_cpus_should_update - Returns if the isolated_cpus mask needs u= pdate + * @prs: new or old partition_root_state + * @parent: parent cpuset + * Return: true if isolated_cpus needs modification, false otherwise + */ +static bool isolated_cpus_should_update(int prs, struct cpuset *parent) +{ + if (!parent) + parent =3D &top_cpuset; + return prs !=3D parent->partition_root_state; +} + /* * partition_xcpus_add - Add new exclusive CPUs to partition * @new_prs: new partition_root_state @@ -1393,6 +1406,42 @@ static bool partition_xcpus_del(int old_prs, struct = cpuset *parent, return isolcpus_updated; } =20 +/* + * isolated_cpus_can_update - check for isolated & nohz_full conflicts + * @add_cpus: cpu mask for cpus that are going to be isolated + * @del_cpus: cpu mask for cpus that are no longer isolated, can be NULL + * Return: false if there is conflict, true otherwise + * + * If nohz_full is enabled and we have isolated CPUs, their combination mu= st + * still leave housekeeping CPUs. + */ +static bool isolated_cpus_can_update(struct cpumask *add_cpus, + struct cpumask *del_cpus) +{ + cpumask_var_t full_hk_cpus; + int res =3D true; + + if (!housekeeping_enabled(HK_TYPE_KERNEL_NOISE)) + return true; + + if (del_cpus && cpumask_weight_and(del_cpus, + housekeeping_cpumask(HK_TYPE_KERNEL_NOISE))) + return true; + + if (!alloc_cpumask_var(&full_hk_cpus, GFP_KERNEL)) + return false; + + cpumask_and(full_hk_cpus, housekeeping_cpumask(HK_TYPE_KERNEL_NOISE), + housekeeping_cpumask(HK_TYPE_DOMAIN)); + cpumask_andnot(full_hk_cpus, full_hk_cpus, isolated_cpus); + cpumask_and(full_hk_cpus, full_hk_cpus, cpu_active_mask); + if (!cpumask_weight_andnot(full_hk_cpus, add_cpus)) + res =3D false; + + free_cpumask_var(full_hk_cpus); + return res; +} + static void update_isolation_cpumasks(bool isolcpus_updated) { int ret; @@ -1551,6 +1600,9 @@ static int remote_partition_enable(struct cpuset *cs,= int new_prs, if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) || cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) return PERR_INVCPUS; + if (isolated_cpus_should_update(new_prs, NULL) && + !isolated_cpus_can_update(tmp->new_cpus, NULL)) + return PERR_HKEEPING; =20 spin_lock_irq(&callback_lock); isolcpus_updated =3D partition_xcpus_add(new_prs, NULL, tmp->new_cpus); @@ -1650,6 +1702,9 @@ static void remote_cpus_update(struct cpuset *cs, str= uct cpumask *xcpus, else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) || cpumask_subset(top_cpuset.effective_cpus, tmp->addmask)) cs->prs_err =3D PERR_NOCPUS; + else if (isolated_cpus_should_update(prs, NULL) && + !isolated_cpus_can_update(tmp->addmask, tmp->delmask)) + cs->prs_err =3D PERR_HKEEPING; if (cs->prs_err) goto invalidate; } @@ -1988,6 +2043,12 @@ static int update_parent_effective_cpumask(struct cp= uset *cs, int cmd, return err; } =20 + if (deleting && isolated_cpus_should_update(new_prs, parent) && + !isolated_cpus_can_update(tmp->delmask, tmp->addmask)) { + cs->prs_err =3D PERR_HKEEPING; + return PERR_HKEEPING; + } + /* * Change the parent's effective_cpus & effective_xcpus (top cpuset * only). @@ -2994,7 +3055,11 @@ static int update_prstate(struct cpuset *cs, int new= _prs) * A change in load balance state only, no change in cpumasks. * Need to update isolated_cpus. */ - isolcpus_updated =3D true; + if ((new_prs =3D=3D PRS_ISOLATED) && + !isolated_cpus_can_update(cs->effective_xcpus, NULL)) + err =3D PERR_HKEEPING; + else + isolcpus_updated =3D true; } else { /* * Switching back to member is always allowed even if it --=20 2.51.1