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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id af79cd13be357-82aad002559sm138039985a.39.2025.09.15.13.43.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Sep 2025 13:43:48 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <969cbdd2-36ed-456c-96f8-d3b53e9ffb71@redhat.com> Date: Mon, 15 Sep 2025 16:43:48 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 7/9] cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping To: Gabriele Monaco , linux-kernel@vger.kernel.org, Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , cgroups@vger.kernel.org Cc: Frederic Weisbecker References: <20250915145920.140180-11-gmonaco@redhat.com> <20250915145920.140180-18-gmonaco@redhat.com> Content-Language: en-US In-Reply-To: <20250915145920.140180-18-gmonaco@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/15/25 10:59 AM, Gabriele Monaco wrote: > 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 | 63 ++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 63 insertions(+) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 81a9239053a7..3cedc3580373 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 +1352,42 @@ static bool partition_xcpus_del(int old_prs, struct cpuset *parent, > return isolcpus_updated; > } > > +/* > + * 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 must > + * 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 = 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 = false; > + > + free_cpumask_var(full_hk_cpus); > + return res; > +} > + > static void update_exclusion_cpumasks(bool isolcpus_updated) > { > int ret; > @@ -1464,6 +1513,9 @@ 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; > > spin_lock_irq(&callback_lock); > isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus); > @@ -1563,6 +1615,9 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus, > else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) || > cpumask_subset(top_cpuset.effective_cpus, tmp->addmask)) > cs->prs_err = PERR_NOCPUS; > + else if (isolated_cpus_should_update(prs, NULL) && > + !isolated_cpus_can_update(tmp->addmask, tmp->delmask)) > + cs->prs_err = PERR_HKEEPING; > if (cs->prs_err) > goto invalidate; > } > @@ -1914,6 +1969,12 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, > return err; > } > > + if (deleting && isolated_cpus_should_update(new_prs, parent) && > + !isolated_cpus_can_update(tmp->delmask, tmp->addmask)) { > + cs->prs_err = PERR_HKEEPING; > + return PERR_HKEEPING; > + } > + > /* > * Change the parent's effective_cpus & effective_xcpus (top cpuset > * only). > @@ -2934,6 +2995,8 @@ static int update_prstate(struct cpuset *cs, int new_prs) > * Need to update isolated_cpus. > */ > isolcpus_updated = true; > + if (!isolated_cpus_can_update(cs->effective_xcpus, NULL)) > + err = PERR_HKEEPING; > } else { > /* > * Switching back to member is always allowed even if it Reviewed-by: Waiman Long