wireguard: ratelimiter: use hrtimer in selftest

Using msleep() is problematic because it's compared against
ratelimiter.c's ktime_get_coarse_boottime_ns(), which means on systems
with slow jiffies (such as UML's forced HZ=100), the result is
inaccurate. So switch to using schedule_hrtimeout().

However, hrtimer gives us access only to the traditional posix timers,
and none of the _COARSE variants. So now, rather than being too
imprecise like jiffies, it's too precise.

One solution would be to give it a large "range" value, but this will
still fire early on a loaded system. A better solution is to align the
timeout to the actual coarse timer, and then round up to the nearest
tick, plus change.

So add the timeout to the current coarse time, and then
schedule_hrtimer() until the absolute computed time.

This should hopefully reduce flakes in CI as well. Note that we keep the
retry loop in case the entire function is running behind, because the
test could still be scheduled out, by either the kernel or by the
hypervisor's kernel, in which case restarting the test and hoping to not
be scheduled out still helps.

Fixes: e7096c13 ("net: WireGuard secure network tunnel")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/wireguard/selftest/ratelimiter.c

@@ -6,28 +6,29 @@
 #ifdef DEBUG
 
 #include <linux/jiffies.h>
+#include <linux/hrtimer.h>
 
 static const struct {
 	bool result;
-	unsigned int msec_to_sleep_before;
+	u64 nsec_to_sleep_before;
 } expected_results[] __initconst = {
 	[0 ... PACKETS_BURSTABLE - 1] = { true, 0 },
 	[PACKETS_BURSTABLE] = { false, 0 },
-	[PACKETS_BURSTABLE + 1] = { true, MSEC_PER_SEC / PACKETS_PER_SECOND },
+	[PACKETS_BURSTABLE + 1] = { true, NSEC_PER_SEC / PACKETS_PER_SECOND },
 	[PACKETS_BURSTABLE + 2] = { false, 0 },
-	[PACKETS_BURSTABLE + 3] = { true, (MSEC_PER_SEC / PACKETS_PER_SECOND) * 2 },
+	[PACKETS_BURSTABLE + 3] = { true, (NSEC_PER_SEC / PACKETS_PER_SECOND) * 2 },
 	[PACKETS_BURSTABLE + 4] = { true, 0 },
 	[PACKETS_BURSTABLE + 5] = { false, 0 }
 };
 
 static __init unsigned int maximum_jiffies_at_index(int index)
 {
-	unsigned int total_msecs = 2 * MSEC_PER_SEC / PACKETS_PER_SECOND / 3;
+	u64 total_nsecs = 2 * NSEC_PER_SEC / PACKETS_PER_SECOND / 3;
 	int i;
 
 	for (i = 0; i <= index; ++i)
-		total_msecs += expected_results[i].msec_to_sleep_before;
-	return msecs_to_jiffies(total_msecs);
+		total_nsecs += expected_results[i].nsec_to_sleep_before;
+	return nsecs_to_jiffies(total_nsecs);
 }
 
 static __init int timings_test(struct sk_buff *skb4, struct iphdr *hdr4,
@@ -42,8 +43,12 @@ static __init int timings_test(struct sk_buff *skb4, struct iphdr *hdr4,
 	loop_start_time = jiffies;
 
 	for (i = 0; i < ARRAY_SIZE(expected_results); ++i) {
-		if (expected_results[i].msec_to_sleep_before)
-			msleep(expected_results[i].msec_to_sleep_before);
+		if (expected_results[i].nsec_to_sleep_before) {
+			ktime_t timeout = ktime_add(ktime_add_ns(ktime_get_coarse_boottime(), TICK_NSEC * 4 / 3),
+						    ns_to_ktime(expected_results[i].nsec_to_sleep_before));
+			set_current_state(TASK_UNINTERRUPTIBLE);
+			schedule_hrtimeout_range_clock(&timeout, 0, HRTIMER_MODE_ABS, CLOCK_BOOTTIME);
+		}
 
 		if (time_is_before_jiffies(loop_start_time +
 					   maximum_jiffies_at_index(i)))
@@ -127,7 +132,7 @@ bool __init wg_ratelimiter_selftest(void)
 	if (IS_ENABLED(CONFIG_KASAN) || IS_ENABLED(CONFIG_UBSAN))
 		return true;
 
-	BUILD_BUG_ON(MSEC_PER_SEC % PACKETS_PER_SECOND != 0);
+	BUILD_BUG_ON(NSEC_PER_SEC % PACKETS_PER_SECOND != 0);
 
 	if (wg_ratelimiter_init())
 		goto out;
@@ -176,7 +181,6 @@ bool __init wg_ratelimiter_selftest(void)
 				test += test_count;
 				goto err;
 			}
-			msleep(500);
 			continue;
 		} else if (ret < 0) {
 			test += test_count;
@@ -195,7 +199,6 @@ bool __init wg_ratelimiter_selftest(void)
 				test += test_count;
 				goto err;
 			}
-			msleep(50);
 			continue;
 		}
 		test += test_count;

kernel/time/hrtimer.c

@@ -2311,6 +2311,7 @@ schedule_hrtimeout_range_clock(ktime_t *expires, u64 delta,
 
 	return !t.task ? 0 : -EINTR;
 }
+EXPORT_SYMBOL_GPL(schedule_hrtimeout_range_clock);
 
 /**
  * schedule_hrtimeout_range - sleep until timeout