tracing: Have the trace_event benchmark thread call cond_resched_rcu_qs() (b980b117) · Commits · e / devices / android_kernel_fairphone_FP4

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" <paulmck@linux.vnet.ibm.com> Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_benchmark.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -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;