linux-kernel - [PATCH 7/5 v2] tracing: Make sure rcu_irq_enter() can work for trace_*

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Message-ID: <20170407134819.6b66b7de@gandalf.local.home>
Date:   Fri, 7 Apr 2017 13:48:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH 7/5 v2] tracing: Make sure rcu_irq_enter() can work for
 trace_*_rcuidle() trace events

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

Stack tracing discovered that there's a small location inside the RCU
infrastructure where calling rcu_irq_enter() does not work. As trace events
use rcu_irq_enter() it must make sure that it is functionable. A check
against rcu_irq_enter_disabled() is added with a WARN_ON_ONCE() as no trace
event should ever be used in that part of RCU. If the warning is triggered,
then the trace event is ignored.

Link: http://lkml.kernel.org/r/20170405093207.404f8deb@gandalf.local.home

Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
Mathieu, is this better? (yeah, i left in functionable, because I like
that word ;-)

include/linux/tracepoint.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index f72fcfe..352f32a 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -151,7 +151,12 @@ extern void syscall_unregfunc(void);
 	} while (0)
 
 #ifndef MODULE
-#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)	\
+#define TRACE_RCU_IRQ_ENTER_CHECK					\
+	if (WARN_ON_ONCE(rcu_irq_enter_disabled()))			\
+		return;							\
+	rcu_irq_enter_irqson()
+
+#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
 	static inline void trace_##name##_rcuidle(proto)		\
 	{								\
 		if (static_key_false(&__tracepoint_##name.key))		\
@@ -159,7 +164,7 @@ extern void syscall_unregfunc(void);
 				TP_PROTO(data_proto),			\
 				TP_ARGS(data_args),			\
 				TP_CONDITION(cond),			\
-				rcu_irq_enter_irqson(),			\
+				PARAMS(TRACE_RCU_IRQ_ENTER_CHECK),	\
 				rcu_irq_exit_irqson());			\
 	}
 #else
-- 
2.9.3