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Fri, 02 Oct 2026 06:11:53 -0700 (PDT) From: Qiliang Yuan Date: Fri, 02 Oct 2026 21:10:30 +0800 Subject: [PATCH v5 10/12] cpuset: Drive kernel-noise isolation via per-CPU hotplug cycling Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261002-wujing-dhm-v5-10-78a6996d87ad@gmail.com> References: <20261002-wujing-dhm-v5-0-78a6996d87ad@gmail.com> In-Reply-To: <20261002-wujing-dhm-v5-0-78a6996d87ad@gmail.com> To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Anna-Maria Behnsen , Tejun Heo , Jonathan Corbet , Shuah Khan , Shuah Khan , Thomas Gleixner Cc: Waiman Long , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Qiliang Yuan X-Mailer: b4 0.13.0 Track A (cpuset_update_sd_hk_unlock) updates the HK_TYPE_KERNEL_NOISE and HK_TYPE_MANAGED_IRQ cpumasks but performs no per-CPU reconfiguration. Tick suppression, RCU callback offloading and managed-IRQ remapping only take effect when the affected CPUs pass through the CPU hotplug machinery. Implement dhm_cycle_isolated_cpus() and call it from cpuset_update_sd_hk_unlock() with cpuset_top_mutex still held: per the locking convention at the top of this file, cpuset_top_mutex is the outermost lock, so remove_cpu()/add_cpu() may freely acquire cpus_write_lock() underneath it. Keeping the mutex held across the whole cycle also matches dhm_prev_isolated's existing "protected by cpuset_top_mutex" comment and prevents a second isolated-partition update from entering cpuset_update_sd_hk_unlock() while a cycle for the previous one is still in flight. On isolation, for each newly-isolated CPU: 1. remove_cpu() - offline; dying callbacks migrate IRQs 2. housekeeping_update_types() - publish this CPU as kernel-noise isolated now that it is actually offline 3. tick_nohz_cpu_isolate() - enable context tracking so the tick is suppressed for this CPU (B0/B3) 4. rcu_nocb_cpu_isolate() - lazy nocb init, spawn kthreads, offload callbacks (B1) 5. add_cpu() - online; tick and IRQ online callbacks reconfigure against the now-published HK masks On de-isolation, the reverse order is applied, publishing the CPU as no longer kernel-noise isolated right after its own remove_cpu() succeeds instead of before any CPU in the batch is touched. The managed-IRQ remapping requires no explicit call: irq_migrate_all_off_this_cpu() (dying callback) and irq_affinity_online_cpu() (online callback) already consult the updated HK_TYPE_MANAGED_IRQ mask. dhm_prev_isolated tracks the previous isolation set so that only CPUs whose state changed are cycled rather than the full isolation set. lockup_detector_hk_update() (B2) is called once after all CPUs are cycled to update the watchdog mask. Some CPUs cannot be taken offline: cpu_is_hotpluggable() rejects a CPU with hotplug disabled in the architecture (e.g. the x86-64 boot CPU), and remove_cpu() itself can still fail for a CPU that passed that filter (e.g. it turns out to be the last CPU in its sched domain, or it is the current tick_do_timer_cpu holder and tick_nohz_cpu_hotpluggable() rejects it). Publishing housekeeping_update_types() per CPU, strictly after that CPU's own remove_cpu() has already succeeded, makes both cases handle themselves: a CPU this function ends up skipping is simply never added to the published mask, so HK_TYPE_KERNEL_NOISE never claims a CPU is isolated while it keeps ticking and running RCU callbacks normally, without needing a separate pre-filter pass or a republish-on-failure step afterwards. Also free newly_isolated/newly_deisolated/cur_isolated on the early return for a no-op update, which previously leaked the allocations. Signed-off-by: Qiliang Yuan --- kernel/cgroup/cpuset.c | 155 ++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 140 insertions(+), 15 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 6213e63cf348d..9fa4bf504c3d9 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -20,6 +20,8 @@ */ #include "cpuset-internal.h" +#include +#include #include #include #include @@ -33,7 +35,9 @@ #include #include #include +#include #include +#include #include #include #include @@ -165,6 +169,14 @@ static cpumask_var_t isolated_hk_cpus; /* T */ static DEFINE_SPINLOCK(dhm_cycling_lock); static cpumask_var_t dhm_cycling_cpus; +/* + * Snapshot of the isolated CPUs from the previous housekeeping update. + * Used to compute the delta (newly isolated / newly de-isolated) so that + * only the changed CPUs are cycled rather than the full isolation set. + * Protected by cpuset_top_mutex. + */ +static cpumask_var_t dhm_prev_isolated; + /* * A flag to force sched domain rebuild at the end of an operation. * It can be set in @@ -1423,6 +1435,108 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus) return false; } +/* + * dhm_cycle_isolated_cpus - Apply kernel-noise isolation via hotplug cycling + * + * For each CPU newly entering isolation: cycle it offline, configure tick + * suppression and RCU callback offloading while it is offline, then bring + * it back online. The managed-IRQ state is handled automatically by the + * existing irq_migrate_all_off_this_cpu() dying callback and the + * irq_affinity_online_cpu() online callback which both consult the + * already-updated HK_TYPE_MANAGED_IRQ mask. + * + * For each CPU leaving isolation: cycle it offline, de-offload RCU and + * restore the tick, then bring it back online. + * + * Called with cpuset_top_mutex held and no other cpuset or hotplug locks + * held: cpuset_top_mutex is the outermost lock, so remove_cpu()/add_cpu() + * may freely take cpus_write_lock() underneath it. + */ +static void dhm_cycle_isolated_cpus(const struct cpumask *new_isolated) +{ + static const unsigned long noise_types = + BIT(HK_TYPE_KERNEL_NOISE) | BIT(HK_TYPE_MANAGED_IRQ); + cpumask_var_t newly_isolated, newly_deisolated, cur_isolated; + int cpu; + + if (!alloc_cpumask_var(&newly_isolated, GFP_KERNEL) || + !alloc_cpumask_var(&newly_deisolated, GFP_KERNEL) || + !alloc_cpumask_var(&cur_isolated, GFP_KERNEL)) { + free_cpumask_var(newly_isolated); + free_cpumask_var(newly_deisolated); + return; + } + + cpumask_andnot(newly_isolated, new_isolated, dhm_prev_isolated); + cpumask_andnot(newly_deisolated, dhm_prev_isolated, new_isolated); + /* cur_isolated tracks the mask actually published so far. */ + cpumask_copy(cur_isolated, dhm_prev_isolated); + cpumask_copy(dhm_prev_isolated, new_isolated); + + if (cpumask_empty(newly_isolated) && cpumask_empty(newly_deisolated)) + goto out_free; + + /* Mark cycling CPUs so cpuset_hotplug_update_tasks skips invalidation */ + spin_lock(&dhm_cycling_lock); + cpumask_or(dhm_cycling_cpus, newly_isolated, newly_deisolated); + spin_unlock(&dhm_cycling_lock); + + /* + * Publish each CPU's kernel-noise/managed-IRQ housekeeping state + * strictly between its own remove_cpu() succeeding and add_cpu() + * bringing it back, never as a batch before the whole cycle. + * housekeeping_update_types() then always describes exactly which + * CPUs are actually ticking and running RCU callbacks normally at + * that instant, including the current tick_do_timer_cpu holder, + * which tick_nohz_cpu_hotpluggable() must see as still a + * housekeeping CPU for as long as it is still online and un-cycled. + */ + for_each_cpu(cpu, newly_isolated) { + if (!cpu_is_hotpluggable(cpu)) { + pr_warn_once("cpuset: CPU%d cannot be isolated (hotplug disabled)\n", + cpu); + cpumask_clear_cpu(cpu, dhm_prev_isolated); + continue; + } + if (remove_cpu(cpu)) { + pr_warn_once("cpuset: failed to offline CPU%d for isolation\n", + cpu); + cpumask_clear_cpu(cpu, dhm_prev_isolated); + continue; + } + cpumask_set_cpu(cpu, cur_isolated); + WARN_ON_ONCE(housekeeping_update_types(noise_types, cur_isolated)); + WARN_ON_ONCE(tick_nohz_cpu_isolate(cpu)); + WARN_ON_ONCE(rcu_nocb_cpu_isolate(cpu)); + WARN_ON_ONCE(add_cpu(cpu)); + } + + for_each_cpu(cpu, newly_deisolated) { + if (remove_cpu(cpu)) { + pr_warn_once("cpuset: failed to offline CPU%d for de-isolation\n", + cpu); + cpumask_set_cpu(cpu, dhm_prev_isolated); + continue; + } + cpumask_clear_cpu(cpu, cur_isolated); + WARN_ON_ONCE(housekeeping_update_types(noise_types, cur_isolated)); + WARN_ON_ONCE(rcu_nocb_cpu_deoffload(cpu)); + tick_nohz_cpu_deisolate(cpu); + WARN_ON_ONCE(add_cpu(cpu)); + } + + spin_lock(&dhm_cycling_lock); + cpumask_clear(dhm_cycling_cpus); + spin_unlock(&dhm_cycling_lock); + + lockup_detector_hk_update(); + +out_free: + free_cpumask_var(newly_isolated); + free_cpumask_var(newly_deisolated); + free_cpumask_var(cur_isolated); +} + /* * cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock * @@ -1439,8 +1553,6 @@ static void cpuset_update_sd_hk_unlock(void) rebuild_sched_domains_locked(); if (update_housekeeping) { - static const unsigned long noise_types = - BIT(HK_TYPE_KERNEL_NOISE) | BIT(HK_TYPE_MANAGED_IRQ); int ret; update_housekeeping = false; @@ -1450,9 +1562,16 @@ static void cpuset_update_sd_hk_unlock(void) cpus_read_unlock(); /* - * housekeeping_update() is now called without holding - * cpus_read_lock and cpuset_mutex. Only cpuset_top_mutex - * is still being held for mutual exclusion. + * housekeeping_update() and housekeeping_update_types() are + * now called without holding cpus_read_lock and cpuset_mutex. + * cpuset_top_mutex stays held all the way through + * dhm_cycle_isolated_cpus() below: per the locking convention + * at the top of this file it is the outermost lock, so it may + * legally nest around the cpus_write_lock() that remove_cpu()/ + * add_cpu() take. Holding it here is also what makes + * dhm_prev_isolated's "protected by cpuset_top_mutex" comment + * true, and keeps a second isolated-partition update from + * entering this function while a cycle is still in flight. */ /* @@ -1464,18 +1583,23 @@ static void cpuset_update_sd_hk_unlock(void) WARN_ON_ONCE(ret); /* - * Only touch the kernel-noise housekeeping masks - * (HK_TYPE_KERNEL_NOISE and HK_TYPE_MANAGED_IRQ) once the - * sched domain update above actually succeeded: HK_TYPE_ - * KERNEL_NOISE must stay a subset of HK_TYPE_DOMAIN, so a CPU - * can never end up tick-suppressed while still scheduled as - * part of the normal (non-isolated) sched domain. The tick, - * RCU and managed-interrupt state is reconfigured as the - * affected CPUs are cycled through the CPU hotplug machinery. + * Only cycle CPUs through hotplug, applying the kernel-noise + * types along the way, when the sched domain update above + * actually succeeded. HK_TYPE_KERNEL_NOISE must stay a + * subset of HK_TYPE_DOMAIN, so a CPU can never end up + * tick-suppressed while still scheduled as part of the + * normal (non-isolated) sched domain. The tick, RCU and + * managed-interrupt state is reconfigured as the affected + * CPUs are cycled through the CPU hotplug machinery; + * dhm_cycle_isolated_cpus() publishes HK_TYPE_KERNEL_NOISE + * and HK_TYPE_MANAGED_IRQ itself, one CPU at a time, strictly + * between that CPU's own remove_cpu() and add_cpu(), so a + * CPU that cpu_is_hotpluggable() rejects (e.g. the current + * tick_do_timer_cpu) is simply never published as isolated. */ if (!ret) - WARN_ON_ONCE(housekeeping_update_types(noise_types, - isolated_hk_cpus)); + dhm_cycle_isolated_cpus(isolated_hk_cpus); + mutex_unlock(&cpuset_top_mutex); } else { cpuset_full_unlock(); @@ -3915,6 +4039,7 @@ int __init cpuset_init(void) BUG_ON(!zalloc_cpumask_var(&isolated_cpus, GFP_KERNEL)); BUG_ON(!zalloc_cpumask_var(&isolated_hk_cpus, GFP_KERNEL)); BUG_ON(!zalloc_cpumask_var(&dhm_cycling_cpus, GFP_KERNEL)); + BUG_ON(!zalloc_cpumask_var(&dhm_prev_isolated, GFP_KERNEL)); cpumask_setall(top_cpuset.cpus_allowed); nodes_setall(top_cpuset.mems_allowed); -- 2.43.0