linux-kernel - Re: [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for trace_*

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Message-ID: <158560784.4550.1491589063819.JavaMail.zimbra@efficios.com>
Date:   Fri, 7 Apr 2017 18:17:43 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
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: Re: [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for
 trace_*_rcuidle() trace events

----- On Apr 7, 2017, at 2:10 PM, rostedt rostedt@...dmis.org wrote:

> 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 (making code boring) Desnoyers <mathieu.desnoyers@...icios.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
> 
> Mathieu,
> 
> There! Are you now satisfied?

Since you reversed the boolean logic from my proposal, perhaps
rename the "rcucheck" argument to "rcudisabled" to reflect the
logic swap ?

Other than that:

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks,

Mathieu

> 
> 
> 
> 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

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com