[rcu/dev] wait extra jiffies for rcu_tasks_verify_self_tests

Commit Message

Zhouyi Zhou May 17, 2022, 12:45 a.m. UTC

Sometimes, the kernel will boot too fast for rcu_tasks_verify_self_tests
to have all required grace periods.

Wait extra jiffies for rcu_tasks_verify_self_tests so as not to punish
people who make Linux boot faster.

Although 'wait extra jiffies' approach may slow down the Linux boot, but
the CONFIG_PROVE_RCU option is only enabled for experts and for test only.

I also considered temporarily reduce the gp_sleep and init_fract before
rcu_tasks_verify_self_tests, but we can only guess those values
from experience.


Reported-by: Matthew Wilcox <[e-mail]>
Suggested-by: Paul E. McKenney <[e-mail]>
Tested-by: Zhouyi Zhou <[e-mail]>
Signed-off-by: Zhouyi Zhou <[e-mail]>
---
 kernel/rcu/tasks.h | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

2.25.1

Patch

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index bd9f2e24f5c7..b1be85da29ec 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1766,7 +1766,38 @@  static int rcu_tasks_verify_self_tests(void)
 {
 	int ret = 0;
 	int i;
+	int delay = 0;
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		if (!tests[i].notrun) {		// still hanging.
+			ret = -1;
+		}
+	}
+
+	if (!ret)
+		return ret;
+
+#ifdef CONFIG_TASKS_RCU
+	delay = rcu_tasks.gp_sleep;
+	if (delay < rcu_tasks.init_fract)
+		delay = rcu_tasks.init_fract;
+#endif
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+	if (delay < rcu_tasks_rude.gp_sleep)
+		delay = rcu_tasks_rude.gp_sleep;
+#endif
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+	if (delay < rcu_tasks_trace.gp_sleep)
+		delay = rcu_tasks_trace.gp_sleep;
+	if (delay < rcu_tasks_trace.init_fract)
+		delay = rcu_tasks_trace.init_fract;
+#endif
+	pr_info("wait extra %d jiffies for rcu tasks self tests\n", 2*delay);
+	schedule_timeout_uninterruptible(2*delay);
+
+	ret = 0;
 
 	for (i = 0; i < ARRAY_SIZE(tests); i++) {
 		if (!tests[i].notrun) {		// still hanging.
--