Commit 565cfb9e authored by Sangmoon Kim's avatar Sangmoon Kim Committed by Paul E. McKenney
Browse files

rcu/tree: Add a trace event for RCU CPU stall warnings 



This commit adds a trace event which allows tracing the beginnings of RCU
CPU stall warnings on systems where sysctl_panic_on_rcu_stall is disabled.

The first parameter is the name of RCU flavor like other trace events.
The second parameter indicates whether this is a stall of an expedited
grace period, a self-detected stall of a normal grace period, or a stall
of a normal grace period detected by some CPU other than the one that
is stalled.

RCU CPU stall warnings are often caused by external-to-RCU issues,
for example, in interrupt handling or task scheduling.  Therefore,
this event uses TRACE_EVENT, not TRACE_EVENT_RCU, to avoid requiring
those interested in tracing RCU CPU stalls to rebuild their kernels
with CONFIG_RCU_TRACE=y.

Reviewed-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: default avatarNeeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: default avatarSangmoon Kim <sangmoon.kim@samsung.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 7e937220

include/trace/events/rcu.h

+28 −0
Original line number Diff line number Diff line
@@ -432,6 +432,34 @@ TRACE_EVENT_RCU(rcu_fqs, 
		  __entry->cpu, __entry->qsevent)

);



/*

 * Tracepoint for RCU stall events. Takes a string identifying the RCU flavor

 * and a string identifying which function detected the RCU stall as follows:

 *

 *	"StallDetected": Scheduler-tick detects other CPU's stalls.

 *	"SelfDetected": Scheduler-tick detects a current CPU's stall.

 *	"ExpeditedStall": Expedited grace period detects stalls.

 */

TRACE_EVENT(rcu_stall_warning,



	TP_PROTO(const char *rcuname, const char *msg),



	TP_ARGS(rcuname, msg),



	TP_STRUCT__entry(

		__field(const char *, rcuname)

		__field(const char *, msg)

	),



	TP_fast_assign(

		__entry->rcuname = rcuname;

		__entry->msg = msg;

	),



	TP_printk("%s %s",

		  __entry->rcuname, __entry->msg)

);



#endif /* #if defined(CONFIG_TREE_RCU) */



/*

kernel/rcu/tree_exp.h

+1 −0
Original line number Diff line number Diff line
@@ -521,6 +521,7 @@ static void synchronize_rcu_expedited_wait(void) 
		if (rcu_stall_is_suppressed())

			continue;

		panic_on_rcu_stall();

		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));

		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",

		       rcu_state.name);

		ndetected = 0;

kernel/rcu/tree_stall.h

+2 −0
Original line number Diff line number Diff line
@@ -536,6 +536,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) 
	 * See Documentation/RCU/stallwarn.rst for info on how to debug

	 * RCU CPU stall warnings.

	 */

	trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected"));

	pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);

	rcu_for_each_leaf_node(rnp) {

		raw_spin_lock_irqsave_rcu_node(rnp, flags);
@@ -606,6 +607,7 @@ static void print_cpu_stall(unsigned long gps) 
	 * See Documentation/RCU/stallwarn.rst for info on how to debug

	 * RCU CPU stall warnings.

	 */

	trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected"));

	pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);

	raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);

	print_cpu_stall_info(smp_processor_id());