Bench mark the cost of doing kmalloc() then kfree()

uaf.c

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/slab.h>

static u64 read_tsc(void)
{
	return (u64)rdtsc_ordered();
}

static void bench_kmalloc(void)
{
	unsigned long long now;
	unsigned long long delta;
	void *p;

	p = kmalloc(8, GFP_KERNEL);

	/* The next kmalloc is expected to use the fast path */
	kfree(p);

	/* Check if the CPU is in performance mode. */
	// $ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

	local_irq_disable();
	now = read_tsc();
	p = kmalloc(8, GFP_KERNEL);
	kfree(p);
	delta = read_tsc() - now;
	local_irq_enable();

	pr_info("Doing kmalloc() then kfree() costs %llu clock cycles\n", delta);

	now = read_tsc();
	delta = read_tsc() - now;
	pr_info("The cost of read_tsc() is %llu ticks\n", delta);

	now = read_tsc();
	WRITE_ONCE(p, NULL);
	delta = read_tsc() - now - delta;

	/* Got a negative value? Need to understand how a CPU works to
	 * answer this question. */
	pr_info("The cost of setting p to NULL is %llu ticks\n", delta);
}

static int __init uaf_init(void)
{
	bench_kmalloc();
	return 0;
}

static void __exit uaf_exit(void)
{
}

module_init(uaf_init)
module_exit(uaf_exit)
MODULE_LICENSE("GPL");