[PATCH 6.18 206/333] kunit: irq: Ensure timer doesnt fire too frequently

Greg Kroah-Hartman
2026-03-17T17:19:52Z

From: Eric Biggers <ebiggers@kernel.org>

commit 201ceb94aa1def0024a7c18ce643e5f65026be06 upstream.

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: 950a81224e8b ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/kunit/run-in-irq-context.h | 44 +++++++++++++++++++-----------
1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/include/kunit/run-in-irq-context.h b/include/kunit/run-in-irq-context.h
index c89b1b1b12dd..bfe60d6cf28d 100644
--- a/include/kunit/run-in-irq-context.h
+++ b/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);
--
2.53.0