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Date: Tue, 11 Apr 2017 18:54:35 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: LKML <linux-kernel@...r.kernel.org> Subject: [PATCH] tracing: Have the trace_event benchmark thread call cond_resched_rcu_qs() From: "Steven Rostedt (VMware)" <rostedt@...dmis.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. Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.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 e49fbe9..16a8cf0 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; -- 2.9.3
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