linux/include/kunit/run-in-irq-context.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Helper function for testing code in interrupt contexts
 *
 * Copyright 2025 Google LLC
 */
#ifndef _KUNIT_RUN_IN_IRQ_CONTEXT_H
#define _KUNIT_RUN_IN_IRQ_CONTEXT_H

#include <kunit/test.h>
#include <linux/timekeeping.h>
#include <linux/hrtimer.h>
#include <linux/workqueue.h>

struct kunit_irq_test_state {
	bool (*func)(void *test_specific_state);
	void *test_specific_state;
	bool task_func_reported_failure;
	bool hardirq_func_reported_failure;
	bool softirq_func_reported_failure;
	atomic_t task_func_calls;
	atomic_t hardirq_func_calls;
	atomic_t softirq_func_calls;
	ktime_t interval;
	struct hrtimer timer;
	struct work_struct bh_work;
};

static enum hrtimer_restart kunit_irq_test_timer_func(struct hrtimer *timer)
{
	struct kunit_irq_test_state *state =
		container_of(timer, typeof(*state), timer);
	int task_calls, hardirq_calls, softirq_calls;

	WARN_ON_ONCE(!in_hardirq());
	task_calls = atomic_read(&state->task_func_calls);
	hardirq_calls = atomic_inc_return(&state->hardirq_func_calls);
	softirq_calls = atomic_read(&state->softirq_func_calls);

	/*
	 * If the timer is firing too often for the softirq or task to ever have
	 * a chance to run, increase the timer interval.  This is needed on very
	 * slow systems.
	 */
	if (hardirq_calls >= 20 && (softirq_calls == 0 || task_calls == 0))
		state->interval = ktime_add_ns(state->interval, 250);

	if (!state->func(state->test_specific_state))
		state->hardirq_func_reported_failure = true;

	hrtimer_forward_now(&state->timer, state->interval);
	queue_work(system_bh_wq, &state->bh_work);
	return HRTIMER_RESTART;
}

static void kunit_irq_test_bh_work_func(struct work_struct *work)
{
	struct kunit_irq_test_state *state =
		container_of(work, typeof(*state), bh_work);

	WARN_ON_ONCE(!in_serving_softirq());
	atomic_inc(&state->softirq_func_calls);

	if (!state->func(state->test_specific_state))
		state->softirq_func_reported_failure = true;
}

/*
 * Helper function which repeatedly runs the given @func in task, softirq, and
 * hardirq context concurrently, and reports a failure to KUnit if any
 * invocation of @func in any context returns false.  @func is passed
 * @test_specific_state as its argument.  At most 3 invocations of @func will
 * run concurrently: one in each of task, softirq, and hardirq context.  @func
 * will continue running until either @max_iterations calls have been made (so
 * long as at least one each runs in task, softirq, and hardirq contexts), or
 * one second has passed.
 *
 * The main purpose of this interrupt context testing is to validate fallback
 * code paths that run in contexts where the normal code path cannot be used,
 * typically due to the FPU or vector registers already being in-use in kernel
 * mode.  These code paths aren't covered when the test code is executed only by
 * the KUnit test runner thread in task context.  The reason for the concurrency
 * is because merely using hardirq context is not sufficient to reach a fallback
 * code path on some architectures; the hardirq actually has to occur while the
 * FPU or vector unit was already in-use in kernel mode.
 *
 * Another purpose of this testing is to detect issues with the architecture's
 * irq_fpu_usable() and kernel_fpu_begin/end() or equivalent functions,
 * especially in softirq context when the softirq may have interrupted a task
 * already using kernel-mode FPU or vector (if the arch didn't prevent that).
 * Crypto functions are often executed in softirqs, so this is important.
 */
static inline void kunit_run_irq_test(struct kunit *test, bool (*func)(void *),
				      int max_iterations,
				      void *test_specific_state)
{
	struct kunit_irq_test_state state = {
		.func = func,
		.test_specific_state = test_specific_state,
		/*
		 * Start with a 5us timer interval.  If the system can't keep
		 * up, kunit_irq_test_timer_func() will increase it.
		 */
		.interval = us_to_ktime(5),
	};
	unsigned long end_jiffies;
	int task_calls, hardirq_calls, softirq_calls;

	/*
	 * Set up a hrtimer (the way we access hardirq context) and a work
	 * struct for the BH workqueue (the way we access softirq context).
	 */
	hrtimer_setup_on_stack(&state.timer, kunit_irq_test_timer_func,
			       CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
	INIT_WORK_ONSTACK(&state.bh_work, kunit_irq_test_bh_work_func);

	/*
	 * Run for up to max_iterations (including at least one task, softirq,
	 * and hardirq), or 1 second, whichever comes first.
	 */
	end_jiffies = jiffies + HZ;
	hrtimer_start(&state.timer, state.interval, HRTIMER_MODE_REL_HARD);
	do {
		if (!func(test_specific_state))
			state.task_func_reported_failure = true;

		task_calls = atomic_inc_return(&state.task_func_calls);
		hardirq_calls = atomic_read(&state.hardirq_func_calls);
		softirq_calls = atomic_read(&state.softirq_func_calls);
	} while ((task_calls + hardirq_calls + softirq_calls < max_iterations ||
		  (task_calls == 0 || hardirq_calls == 0 ||
		   softirq_calls == 0)) &&
		 !time_after(jiffies, end_jiffies));

	/* Cancel the timer and work. */
	hrtimer_cancel(&state.timer);
	flush_work(&state.bh_work);

	/* Sanity check: the timer and BH functions should have been run. */
	KUNIT_EXPECT_GT_MSG(test, atomic_read(&state.hardirq_func_calls), 0,
			    "Timer function was not called");
	KUNIT_EXPECT_GT_MSG(test, atomic_read(&state.softirq_func_calls), 0,
			    "BH work function was not called");

	/* Check for failure reported from any context. */
	KUNIT_EXPECT_FALSE_MSG(test, state.task_func_reported_failure,
			       "Failure reported from task context");
	KUNIT_EXPECT_FALSE_MSG(test, state.hardirq_func_reported_failure,
			       "Failure reported from hardirq context");
	KUNIT_EXPECT_FALSE_MSG(test, state.softirq_func_reported_failure,
			       "Failure reported from softirq context");
}

#endif /* _KUNIT_RUN_IN_IRQ_CONTEXT_H */