From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 15BB2314B82 for ; Tue, 2 Sep 2025 14:33:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756823594; cv=none; b=fEDhu7oUfIDWvoijkuoB/w4/O08OiuIsDPLyw5dug09PZ/9QoQj041jNn1GrjsBpqZzkttxoDr32mSECbtT0h/rdMVaZH4X0Z4+P2KUwBmFUld9lcvYWBfPaqAJwNh5rluBd9MEhUjG8lb32WlM3gx/tH3uNHwAS09QN91J+U5o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756823594; c=relaxed/simple; bh=tNlTZRMk9cfEFZgxMF0Jg6O3ggSosuJWQym6OxjCUwM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OBum0O9f5YMSrlSzfjX0KruImAvF0eX395CDNAx+/QJQWBk9Kem+yHlnlF3bNA+ORMLwOEALwseGyxBZMJMVdn78h259zm+kjARoBMuDnq1l6u8Td+mykQSVT4mJnB08FbeE1O/1V13cAXNvH8UqfcRjwgCMOYGBD2S0uemzy/Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Iq1MNYhZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Iq1MNYhZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BAC1C4CEED; Tue, 2 Sep 2025 14:33:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756823591; bh=tNlTZRMk9cfEFZgxMF0Jg6O3ggSosuJWQym6OxjCUwM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Iq1MNYhZxvpK5n3aXgMxR4URkBMwxYJdPAB9p543QjuLuvjl6qCOIZgEck4p0DrfX u/+/Rsydp6Xf9kH9SEkabCcQDu8m9aP9cRQmKUG04jeglKFMOih6/sdetBRImCcXmY DyNfHIJc2Wz+/xfcNwbsnF0YwaydKSuMYJssbNtahwqgEGI7uUBbwnghczKKG0n62B wg2m5eHbuE4N7XUeSFbUhqTLaKNeHQIc0UFIOKjOOJfWWE195TMQa0IzBnkfet2aqo nfzswoPlob02q9prs2fkklTbE36PxH1LGdj5Nggkvd2jJmZl9KiBo3b6j557bDGcTT u5XSOG8xITa+g== Date: Tue, 2 Sep 2025 16:33:08 +0200 From: Frederic Weisbecker To: Gabriele Monaco Cc: linux-kernel@vger.kernel.org, Anna-Maria Behnsen , Thomas Gleixner , Waiman Long Subject: Re: [PATCH v10 7/8] cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping Message-ID: References: <20250806093855.86469-1-gmonaco@redhat.com> <20250806093855.86469-8-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250806093855.86469-8-gmonaco@redhat.com> Le Wed, Aug 06, 2025 at 11:38:54AM +0200, Gabriele Monaco a écrit : > 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 > Signed-off-by: Gabriele Monaco > --- > kernel/cgroup/cpuset.c | 57 ++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 57 insertions(+) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 6e3f44ffaa21..7b66ccedbc53 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1275,6 +1275,19 @@ static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus > cpumask_andnot(isolated_cpus, isolated_cpus, xcpus); > } > > +/* > + * isolated_cpus_should_update - Returns if the isolated_cpus mask needs update > + * @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 = &top_cpuset; > + return prs != parent->partition_root_state; > +} > + > /* > * partition_xcpus_add - Add new exclusive CPUs to partition > * @new_prs: new partition_root_state > @@ -1339,6 +1352,36 @@ static bool partition_xcpus_del(int old_prs, struct cpuset *parent, > return isolcpus_updated; > } > > +/* > + * isolcpus_nohz_conflict - check for isolated & nohz_full conflicts > + * @new_cpus: cpu mask for cpus that are going to be isolated > + * Return: true if there is conflict, false otherwise > + * > + * If nohz_full is enabled and we have isolated CPUs, their combination must > + * still leave housekeeping CPUs. > + */ > +static bool isolcpus_nohz_conflict(struct cpumask *new_cpus) > +{ > + cpumask_var_t full_hk_cpus; > + int res = false; > + > + if (!housekeeping_enabled(HK_TYPE_KERNEL_NOISE)) > + return false; > + > + if (!alloc_cpumask_var(&full_hk_cpus, GFP_KERNEL)) > + return true; > + > + 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_online_mask); > + if (!cpumask_weight_andnot(full_hk_cpus, new_cpus)) > + res = true; > + > + free_cpumask_var(full_hk_cpus); > + return res; > +} > + > static void update_exclusion_cpumasks(bool isolcpus_updated) > { > int ret; > @@ -1464,6 +1507,9 @@ 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) && > + isolcpus_nohz_conflict(tmp->new_cpus)) If you resend this patchset, can you rename isolcpus_nohz_conflict() to isolated_cpus_can_update(). I intend to put more conditions in there that are not related to nohz, also this aligns with "isolated_cpus_should_update()" name. Thanks! -- Frederic Weisbecker SUSE Labs