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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8081076843csm88708785a.0.2025.09.02.12.14.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Sep 2025 12:14:45 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <647dabe8-f2ee-4b7c-87c3-b96db79cce7c@redhat.com> Date: Tue, 2 Sep 2025 15:14:44 -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 v10 7/8] cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping To: Gabriele Monaco , linux-kernel@vger.kernel.org, Anna-Maria Behnsen , Frederic Weisbecker , Thomas Gleixner References: <20250806093855.86469-1-gmonaco@redhat.com> <20250806093855.86469-8-gmonaco@redhat.com> Content-Language: en-US In-Reply-To: <20250806093855.86469-8-gmonaco@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/6/25 5:38 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 | 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)) > + return PERR_HKEEPING; > > spin_lock_irq(&callback_lock); > isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus); > @@ -1563,6 +1609,9 @@ 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) && > + isolcpus_nohz_conflict(tmp->addmask)) > + cs->prs_err = PERR_HKEEPING; > if (cs->prs_err) > goto invalidate; > } > @@ -1914,6 +1963,12 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, > return err; > } > > + if (deleting && isolated_cpus_should_update(new_prs, parent) && > + isolcpus_nohz_conflict(tmp->delmask)) { > + cs->prs_err = PERR_HKEEPING; > + return PERR_HKEEPING; > + } > + > /* > * Change the parent's effective_cpus & effective_xcpus (top cpuset > * only). > @@ -2934,6 +2989,8 @@ static int update_prstate(struct cpuset *cs, int new_prs) > * Need to update isolated_cpus. > */ > isolcpus_updated = true; > + if (isolcpus_nohz_conflict(cs->effective_xcpus)) > + err = PERR_HKEEPING; > } else { > /* > * Switching back to member is always allowed even if it As I said in my comment to Frederic patch series that in both remote_cpus_update() and update_parent_effective_cpumask(), some new CPUs can be added to the isolation list while other CPUs can be removed from it. So isolcpus_nohz_conflict() should include both set in its analysis to avoid false positive. Essentally, if the CPUs removed from the isolated_cpus intersect with the nohz_full housekeeping mask, there is no conflict. Cheers, Longman