--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -6,6 +6,10 @@
 #include <linux/sched/isolation.h>
 #include <linux/sched/clock.h>
 #include <linux/bsearch.h>
+#include <linux/delay.h>
+#ifdef CONFIG_SCHED_CACHE
+int sds_window_cpu = -1; /* SDS-WITNESS */
+#endif
 #include "sched.h"
 
 DEFINE_MUTEX(sched_domains_mutex);
@@ -828,6 +832,16 @@
 	dirty_sched_domain_sysctl(cpu);
 	destroy_sched_domains(tmp);
 
+	/*
+	 * SDS-WITNESS: widen the window between entering the RCU removal
+	 * phase (destroy_sched_domains) and publishing the new per-CPU
+	 * pointers (update_top_cache_domain).  Verification only.
+	 */
+	WRITE_ONCE(sds_window_cpu, cpu);
+	pr_info("SDS-WINDOW: cpu=%d\n", cpu);
+	mdelay(100);
+	pr_info("SDS-STORE: cpu=%d\n", cpu);
+
 	update_top_cache_domain(cpu);
 }
 
@@ -3502,3 +3516,63 @@
 	partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
 	sched_domains_mutex_unlock();
 }
+
+/* ---------------- SDS-WITNESS: verification instrumentation ---------------- */
+/*
+ * Reacts to the first window of a detach/build pass (cpu 0), reports a
+ * quiescent state after the grace period has started, then loads the old
+ * per-CPU domain pointer, holds the RCU read-side section across the
+ * callback, and dereferences the domain.  With the mdelay(100) in
+ * cpu_attach_domain() the window is wide enough to load the old pointer
+ * after call_rcu() and before the per-CPU store.
+ */
+#ifdef CONFIG_SCHED_CACHE
+#include <linux/kthread.h>
+
+#define SDS_WITNESS_CPU		0
+#define SDS_WITNESS_HOLD_MS	1500
+
+static int sds_witness_fn(void *unused)
+{
+	struct sched_domain *sd;
+	struct sched_domain_shared *sds;
+
+	while (!kthread_should_stop()) {
+		if (READ_ONCE(sds_window_cpu) != SDS_WITNESS_CPU) {
+			msleep(1);
+			continue;
+		}
+		WRITE_ONCE(sds_window_cpu, -1);
+
+		/* QS after the GP started, before entering the section. */
+		msleep(5);
+
+		rcu_read_lock();
+		sd = rcu_dereference_all(per_cpu(sd_llc, SDS_WITNESS_CPU));
+		if (sd) {
+			pr_info("SDS-LOAD: cpu=%d sd=%px\n",
+				SDS_WITNESS_CPU, (void *)sd);
+			msleep(SDS_WITNESS_HOLD_MS);
+			sds = rcu_dereference_all(sd->shared);
+			pr_info("SDS-WITNESS: cpu=%d sd=%px flags=%x shared=%px nr_busy=%d\n",
+				SDS_WITNESS_CPU, (void *)sd,
+				(unsigned int)READ_ONCE(sd->flags), (void *)sds,
+				sds ? atomic_read(&sds->nr_busy_cpus) : -1);
+		} else {
+			pr_info("SDS-LOAD: cpu=%d NULL\n", SDS_WITNESS_CPU);
+		}
+		rcu_read_unlock();
+		msleep(10);
+	}
+
+	return 0;
+}
+
+static int __init sds_witness_init(void)
+{
+	pr_info("SDS-WITNESS: starting, target cpu %d\n", SDS_WITNESS_CPU);
+	kthread_run(sds_witness_fn, NULL, "sds_witness");
+	return 0;
+}
+late_initcall(sds_witness_init);
+#endif