kunit: irq: Ensure timer doesn't fire too frequently

Fix a bug where kunit_run_irq_test() could hang if the system is too
slow.  This was noticed with the crypto library tests in certain VMs.

Specifically, if kunit_irq_test_timer_func() and the associated hrtimer
code took over 5us to run, then the CPU would spend all its time
executing that code in hardirq context.  As a result, the task executing
kunit_run_irq_test() never had a chance to run, exit the loop, and
cancel the timer.

To fix it, make kunit_irq_test_timer_func() increase the timer interval
when the other contexts aren't having a chance to run.

Fixes: 950a812 ("lib/crypto: tests: Add hash-test-template.h and gen-hash-testvecs.py")
Cc: stable@vger.kernel.org
Reviewed-by: David Gow <david@davidgow.net>
Link: https://lore.kernel.org/r/20260224033751.97615-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Author: Eric Biggers

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

@@ -12,16 +12,16 @@
 #include <linux/hrtimer.h>
 #include <linux/workqueue.h>
 
-#define KUNIT_IRQ_TEST_HRTIMER_INTERVAL us_to_ktime(5)
-
 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;
 };
@@ -30,14 +30,25 @@ 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());
-	atomic_inc(&state->hardirq_func_calls);
+	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, KUNIT_IRQ_TEST_HRTIMER_INTERVAL);
+	hrtimer_forward_now(&state->timer, state->interval);
 	queue_work(system_bh_wq, &state->bh_work);
 	return HRTIMER_RESTART;
 }
@@ -86,10 +97,14 @@ static inline void kunit_run_irq_test(struct kunit *test, bool (*func)(void *),
 	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 hardirq_calls, softirq_calls;
-	bool allctx = false;
+	int task_calls, hardirq_calls, softirq_calls;
 
 	/*
 	 * Set up a hrtimer (the way we access hardirq context) and a work
@@ -104,21 +119,18 @@ static inline void kunit_run_irq_test(struct kunit *test, bool (*func)(void *),
 	 * and hardirq), or 1 second, whichever comes first.
 	 */
 	end_jiffies = jiffies + HZ;
-	hrtimer_start(&state.timer, KUNIT_IRQ_TEST_HRTIMER_INTERVAL,
-		      HRTIMER_MODE_REL_HARD);
-	for (int task_calls = 0, calls = 0;
-	     ((calls < max_iterations) || !allctx) &&
-	     !time_after(jiffies, end_jiffies);
-	     task_calls++) {
+	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);
-		calls = task_calls + hardirq_calls + softirq_calls;
-		allctx = (task_calls > 0) && (hardirq_calls > 0) &&
-			 (softirq_calls > 0);
-	}
+	} 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);