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Subject[PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events
From: "Steven Rostedt (VMware)" <rostedt@goodmis.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 (making code boring) Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---

Mathieu,

There! Are you now satisfied?



include/linux/tracepoint.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index f72fcfe..7f98d50 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -128,7 +128,7 @@ extern void syscall_unregfunc(void);
* as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just
* "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto".
*/
-#define __DO_TRACE(tp, proto, args, cond, prercu, postrcu) \
+#define __DO_TRACE(tp, proto, args, cond, rcucheck, prercu, postrcu) \
do { \
struct tracepoint_func *it_func_ptr; \
void *it_func; \
@@ -136,6 +136,8 @@ extern void syscall_unregfunc(void);
\
if (!(cond)) \
return; \
+ if (rcucheck) \
+ return; \
prercu; \
rcu_read_lock_sched_notrace(); \
it_func_ptr = rcu_dereference_sched((tp)->funcs); \
@@ -151,7 +153,7 @@ extern void syscall_unregfunc(void);
} while (0)

#ifndef MODULE
-#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
+#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)) \
@@ -159,6 +161,7 @@ extern void syscall_unregfunc(void);
TP_PROTO(data_proto), \
TP_ARGS(data_args), \
TP_CONDITION(cond), \
+ WARN_ON_ONCE(rcu_irq_enter_disabled()),\
rcu_irq_enter_irqson(), \
rcu_irq_exit_irqson()); \
}
@@ -186,7 +189,7 @@ extern void syscall_unregfunc(void);
__DO_TRACE(&__tracepoint_##name, \
TP_PROTO(data_proto), \
TP_ARGS(data_args), \
- TP_CONDITION(cond),,); \
+ TP_CONDITION(cond),0,,); \
if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
rcu_read_lock_sched_notrace(); \
rcu_dereference_sched(__tracepoint_##name.funcs);\
--
2.9.3
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