Re: [PATCH] tracing: reject invalid preemptirq_delay_test CPU affinity

[Steven Rostedt <rostedt@goodmis.org>]

On Fri,  5 Jun 2026 00:40:06 +0000
Samuel Moelius <sam.moelius@trailofbits.com> wrote:

> 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;

Just add the check to the preemptirq_delay_run() function where it
tests affinity. Who cares if it created the thread or not. It's just a
test.

-- Steve


> +		}
> +	}
> +
>  	init_completion(&done);
>  
>  	snprintf(task_name, sizeof(task_name), "%s_test", test_mode);