From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
The trace_event benchmark thread runs in kernel space in an infinite loop
while also calling cond_resched() in case anything else wants to schedule
in. Unfortunately, on a PREEMPT kernel, that makes it a nop, in which case,
this will never voluntarily schedule. That will cause synchronize_rcu_tasks()
to forever block on this thread, while it is running.
This is exactly what cond_resched_rcu_qs() is for. Use that instead.
Acked-by: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
kernel/trace/trace_benchmark.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c
index e49fbe901cfc..16a8cf02eee9 100644
--- a/kernel/trace/trace_benchmark.c
+++ b/kernel/trace/trace_benchmark.c
@@ -153,10 +153,18 @@ static int benchmark_event_kthread(void *arg)
trace_do_benchmark();
/*
- * We don't go to sleep, but let others
- * run as well.
+ * We don't go to sleep, but let others run as well.
+ * This is bascially a "yield()" to let any task that
+ * wants to run, schedule in, but if the CPU is idle,
+ * we'll keep burning cycles.
+ *
+ * Note the _rcu_qs() version of cond_resched() will
+ * notify synchronize_rcu_tasks() that this thread has
+ * passed a quiescent state for rcu_tasks. Otherwise
+ * this thread will never voluntarily schedule which would
+ * block synchronize_rcu_tasks() indefinitely.
*/
- cond_resched();
+ cond_resched_rcu_qs();
}
return 0;
--
2.10.2
