The event allows us to trace the RCU stall when
sysctl_panic_on_rcu_stall is disabled.
The first parameter is the name of RCU flavour like other trace
events. The second one shows us which function detected stalls.
The RCU stall is mainly caused by external factors such as interrupt
handling or task scheduling or something else. Therefore, this event
uses TRACE_EVENT macro, not dedicated one, so that someone interested
in the RCU stall can use it without CONFIG_RCU_TRACE.
Signed-off-by: Sangmoon Kim <sangmoon.kim@xxxxxxxxxxx>
---
include/trace/events/rcu.h | 28 ++++++++++++++++++++++++++++
kernel/rcu/tree_exp.h | 2 ++
kernel/rcu/tree_stall.h | 2 ++
3 files changed, 32 insertions(+)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 155b5cb43cfd..8476f3161bd0 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -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) */
/*
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 8760b6ead770..c16618284cb2 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -566,6 +566,8 @@ static void synchronize_rcu_expedited_wait(void)
dump_cpu_task(cpu);
}
}
+ trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
+
jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
}
}
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 70d48c52fabc..e93df4fac5b1 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -531,6 +531,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
rcu_check_gp_kthread_starvation();
+ trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected"));
panic_on_rcu_stall();
rcu_force_quiescent_state(); /* Kick them all. */
@@ -575,6 +576,7 @@ static void print_cpu_stall(unsigned long gps)
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected"));
panic_on_rcu_stall();
/*
--
2.17.1
