linux-kernel - Re: [PATCH -next] tracepoint: ipi: don't trace IPI on offline CPUs

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Message-ID: <20160309110539.603293db@gandalf.local.home>
Date:	Wed, 9 Mar 2016 11:05:39 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH -next] tracepoint: ipi: don't trace IPI on offline CPUs

On Wed,  9 Mar 2016 12:22:22 +0000
Sudeep Holla <sudeep.holla@....com> wrote:


> Hi Steven,
> 
> I observed that in "include/linux/tracepoint.h", we have
> #define __DO_TRACE(tp, proto, args, cond, prercu, postrcu)
> ...
>                  if (!cpu_online(raw_smp_processor_id()))
>                          return;
> 
>                  if (!(cond))
>                          return;
> ...
> 
> where !cond check seems reduntant if it's cpu_online check.
> So, does this patch handle the warning correctly or is there any better
> way ? I did see few traces with same condition, just thought of checking
> with you.
> 

Bah, I forgot that we have lockdep checks for when the event isn't
enabled. Can you try this patch:

-- Steve

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index acfdbf353a0b..be586c632a0c 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -134,9 +134,6 @@ extern void syscall_unregfunc(void);
 		void *it_func;						\
 		void *__data;						\
 									\
-		if (!cpu_online(raw_smp_processor_id()))		\
-			return;						\
-									\
 		if (!(cond))						\
 			return;						\
 		prercu;							\
@@ -343,15 +340,19 @@ extern void syscall_unregfunc(void);
  * "void *__data, proto" as the callback prototype.
  */
 #define DECLARE_TRACE_NOARGS(name)					\
-		__DECLARE_TRACE(name, void, , 1, void *__data, __data)
+	__DECLARE_TRACE(name, void, ,					\
+			cpu_online(raw_smp_processor_id()),		\
+			void *__data, __data)
 
 #define DECLARE_TRACE(name, proto, args)				\
-		__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), 1,	\
-				PARAMS(void *__data, proto),		\
-				PARAMS(__data, args))
+	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),		\
+			cpu_online(raw_smp_processor_id()),		\
+			PARAMS(void *__data, proto),			\
+			PARAMS(__data, args))
 
 #define DECLARE_TRACE_CONDITION(name, proto, args, cond)		\
-	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), PARAMS(cond), \
+	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),		\
+			cpu_online(raw_smp_processor_id()) && (PARAMS(cond)), \
 			PARAMS(void *__data, proto),			\
 			PARAMS(__data, args))