preemptirq_delay_test accepts cpu_affinity as a module parameter and,
when it is non-negative, writes that CPU directly into a temporary
cpumask from the worker thread.  Values outside nr_cpu_ids can set a
bit outside the allocated cpumask before the test reports a normal
affinity error.

Validate the requested CPU before starting the worker thread, and
return -EINVAL for invalid affinity requests.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
---
 kernel/trace/preemptirq_delay_test.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
index acb0c971a408..0f017799754a 100644
--- a/kernel/trace/preemptirq_delay_test.c
+++ b/kernel/trace/preemptirq_delay_test.c
@@ -14,6 +14,7 @@
 #include <linux/kthread.h>
 #include <linux/module.h>
 #include <linux/printk.h>
+#include <linux/cpumask.h>
 #include <linux/string.h>
 #include <linux/sysfs.h>
 #include <linux/completion.h>
@@ -152,6 +153,15 @@ static int preemptirq_run_test(void)
 	struct task_struct *task;
 	char task_name[50];
 
+	if (cpu_affinity > -1) {
+		unsigned int cpu = cpu_affinity;
+
+		if (cpu >= nr_cpu_ids || !cpu_possible(cpu)) {
+			pr_err("cpu_affinity:%d, invalid CPU\n", cpu_affinity);
+			return -EINVAL;
+		}
+	}
+
 	init_completion(&done);
 
 	snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
-- 
2.43.0