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Commit d54b6eeb authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
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tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events 

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.

Restructure the __DO_TRACE() a bit to get rid of the prercu and postrcu,
and just have an rcucheck that does the work from within the _DO_TRACE()
macro. gcc optimization will compile out the rcucheck=0 case.

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



Acked-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 03ecd3f4

include/linux/tracepoint.h

+11 −8
Original line number Diff line number Diff line
@@ -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)			\

	do {								\

		struct tracepoint_func *it_func_ptr;			\

		void *it_func;						\
@@ -136,7 +136,11 @@ extern void syscall_unregfunc(void); 
									\

		if (!(cond))						\

			return;						\

		prercu;							\

		if (rcucheck) {						\

			if (WARN_ON_ONCE(rcu_irq_enter_disabled()))	\

				return;					\

			rcu_irq_enter_irqson();				\

		}							\

		rcu_read_lock_sched_notrace();				\

		it_func_ptr = rcu_dereference_sched((tp)->funcs);	\

		if (it_func_ptr) {					\
@@ -147,7 +151,8 @@ extern void syscall_unregfunc(void); 
			} while ((++it_func_ptr)->func);		\

		}							\

		rcu_read_unlock_sched_notrace();			\

		postrcu;						\

		if (rcucheck)						\

			rcu_irq_exit_irqson();				\

	} while (0)



#ifndef MODULE
@@ -158,9 +163,7 @@ extern void syscall_unregfunc(void); 
			__DO_TRACE(&__tracepoint_##name,		\

				TP_PROTO(data_proto),			\

				TP_ARGS(data_args),			\

				TP_CONDITION(cond),			\

				rcu_irq_enter_irqson(),			\

				rcu_irq_exit_irqson());			\

				TP_CONDITION(cond), 1);			\

	}

#else

#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)
@@ -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);\