[PATCH v4 09/11] cpuset: drive kernel-noise isolation via per-CPU hotplug cycling

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() after all cpuset and hotplug locks are
released so that remove_cpu()/add_cpu() may acquire cpus_write_lock
without violating the cpu_hotplug_lock > cpuset_top_mutex order.

On isolation, for each newly-isolated CPU:
  1. remove_cpu()              - offline; dying callbacks migrate IRQs
  2. tick_nohz_cpu_isolate()  - add to tick_nohz_full_mask, enable
                                 context tracking (B0/B3)
  3. rcu_nocb_cpu_isolate()   - lazy nocb init, spawn kthreads, offload
                                 callbacks (B1)
  4. add_cpu()                 - online; tick and IRQ online callbacks
                                 reconfigure against updated HK masks

On de-isolation, the reverse order is applied.  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.

CPUs with hotplug disabled (e.g. x86-64 boot CPU) cannot be taken
offline and are skipped.  On any remove_cpu() failure the corresponding
CPU is cleared from dhm_prev_isolated so the next isolation attempt
will retry rather than silently treating it as already isolated.
Symmetrically, a de-isolation remove_cpu() failure re-sets the bit in
dhm_prev_isolated so the CPU remains tracked as still isolated.

Co-developed-by: Qiliang Yuan <[email protected]>
Signed-off-by: Qiliang Yuan <[email protected]>
Signed-off-by: Jing Wu <[email protected]>
---
 kernel/cgroup/cpuset.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 62eb6798a0c3e..d9e121bf14292 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -20,6 +20,8 @@
  */
 #include "cpuset-internal.h"
 
+#include <linux/cpu.h>
+#include <linux/cpuhplock.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
@@ -33,7 +35,9 @@
 #include <linux/sched/task.h>
 #include <linux/security.h>
 #include <linux/oom.h>
+#include <linux/nmi.h>
 #include <linux/sched/isolation.h>
+#include <linux/tick.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 #include <linux/task_work.h>
@@ -164,6 +168,14 @@ 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
@@ -1339,6 +1351,84 @@ 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.
+ *
+ * Must be called without any cpuset or hotplug locks held.
+ */
+static void dhm_cycle_isolated_cpus(const struct cpumask *new_isolated)
+{
+	cpumask_var_t newly_isolated, newly_deisolated;
+	int cpu;
+
+	if (!alloc_cpumask_var(&newly_isolated, GFP_KERNEL) ||
+	    !alloc_cpumask_var(&newly_deisolated, GFP_KERNEL)) {
+		free_cpumask_var(newly_isolated);
+		return;
+	}
+
+	cpumask_andnot(newly_isolated, new_isolated, dhm_prev_isolated);
+	cpumask_andnot(newly_deisolated, dhm_prev_isolated, new_isolated);
+	cpumask_copy(dhm_prev_isolated, new_isolated);
+
+	if (cpumask_empty(newly_isolated) && cpumask_empty(newly_deisolated))
+		return;
+
+	/* 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);
+
+	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;
+		}
+		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;
+		}
+		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();
+
+	free_cpumask_var(newly_isolated);
+	free_cpumask_var(newly_deisolated);
+}
+
 /*
  * cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock
  *
@@ -1386,6 +1476,13 @@ static void cpuset_update_sd_hk_unlock(void)
 		WARN_ON_ONCE(housekeeping_update_types(noise_types,
 						       isolated_hk_cpus));
 		mutex_unlock(&cpuset_top_mutex);
+
+		/*
+		 * All cpuset and hotplug locks are released.  Cycle each
+		 * affected CPU through hotplug to activate tick suppression,
+		 * RCU callback offloading and managed-IRQ remapping.
+		 */
+		dhm_cycle_isolated_cpus(isolated_hk_cpus);
 	} else {
 		cpuset_full_unlock();
 	}
@@ -3717,6 +3814,7 @@ 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