Patch "tracing: Fix check for cpu online when event is disabled" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    tracing: Fix check for cpu online when event is disabled

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-fix-check-for-cpu-online-when-event-is-disabled.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From dc17147de328a74bbdee67c1bf37d2f1992de756 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
Date: Wed, 9 Mar 2016 11:58:41 -0500
Subject: tracing: Fix check for cpu online when event is disabled

From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>

commit dc17147de328a74bbdee67c1bf37d2f1992de756 upstream.

Commit f37755490fe9b ("tracepoints: Do not trace when cpu is offline") added
a check to make sure that tracepoints only get called when the cpu is
online, as it uses rcu_read_lock_sched() for protection.

Commit 3a630178fd5f3 ("tracing: generate RCU warnings even when tracepoints
are disabled") added lockdep checks (including rcu checks) for events that
are not enabled to catch possible RCU issues that would only be triggered if
a trace event was enabled. Commit f37755490fe9b only stopped the warnings
when the trace event was enabled but did not prevent warnings if the trace
event was called when disabled.

To fix this, the cpu online check is moved to where the condition is added
to the trace event. This will place the cpu online check in all places that
it may be used now and in the future.

Fixes: f37755490fe9b ("tracepoints: Do not trace when cpu is offline")
Fixes: 3a630178fd5f3 ("tracing: generate RCU warnings even when tracepoints are disabled")
Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/linux/tracepoint.h |   17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -148,9 +148,6 @@ extern void syscall_unregfunc(void);
 		void *it_func;						\
 		void *__data;						\
 									\
-		if (!cpu_online(raw_smp_processor_id()))		\
-			return;						\
-									\
 		if (!(cond))						\
 			return;						\
 		prercu;							\
@@ -357,15 +354,19 @@ 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))
 


Patches currently in stable-queue which might be from rostedt@goodmis.org are

queue-4.4/tracing-fix-check-for-cpu-online-when-event-is-disabled.patch