From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org>
Having the RCU unsafe checker running when function graph is enabled
can cause a live lock. That's because the RCU unsafe checker enables
full lockdep debugging on RCU which does a lot of interal calls that
may be traced by the function graph tacer. This adds quite a bit of
overhead and can possibly live lock the system.
Just do not do the RCU unsafe checks when function graph tracer is
enabled.
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
kernel/trace/ftrace.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 69b7f62..310b727 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5118,6 +5118,12 @@ int register_ftrace_graph(trace_func_graph_ret_t retfunc,
goto out;
}
+ /*
+ * The Unsafe RCU checker can live lock function graph tracing.
+ * It's best to just disable it while doing the fgraph tracing.
+ */
+ ftrace_unsafe_rcu_checker_disable();
+
ftrace_graph_return = retfunc;
ftrace_graph_entry = entryfunc;
@@ -5141,6 +5147,7 @@ void unregister_ftrace_graph(void)
ftrace_shutdown(&global_ops, FTRACE_STOP_FUNC_RET);
unregister_pm_notifier(&ftrace_suspend_notifier);
unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
+ ftrace_unsafe_rcu_checker_enable();
out:
mutex_unlock(&ftrace_lock);
--
1.7.10.4
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