Patch "tracing: Fix check for cpu online when event is disabled" has been added to the 3.10-stable tree

From dc17147de328a74bbdee67c1bf37d2f1992de756 Mon Sep 17 00:00:00 2001

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 3.10-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-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From dc17147de328a74bbdee67c1bf37d2f1992de756 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <[email protected]>
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) <[email protected]>

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 <[email protected]>

Tested-by Sudeep Holla <[email protected]>

Signed-off-by Steven Rostedt <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

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

include/linux/tracepoint.h +9 -8

@@ -129,9 +129,6 @@ static inline void tracepoint_synchroniz
 		void *it_func;						\
 		void *__data;						\
 									\
-		if (!cpu_online(raw_smp_processor_id()))		\
-			return;						\
-									\
 		if (!(cond))						\
 			return;						\
 		prercu;							\

@@ -265,15 +262,19 @@ static inline void tracepoint_synchroniz
  * "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 [email protected] are

queue-3.10/tracing-fix-check-for-cpu-online-when-event-is-disabled.patch --
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Quoted 12 lines · Greg Kroah-Hartman

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 3.10-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-3.10 subdirectory.

Quoted 3 lines

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Please note that this patch was tagged for stable 3.18+.

Quoted 12 lines · Greg Kroah-Hartman

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 3.10-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-3.10 subdirectory.

Quoted 3 lines

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Please note that this patch was tagged for stable 3.18+.

Quoted 4 lines

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.

Quoted 7 lines

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.

Quoted 13 lines · On Mon, 14 Mar 2016 17:18:52 +0000 Luis Henriques…

Quoted 12 lines · Greg Kroah-Hartman

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 3.10-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-3.10 subdirectory.

Quoted 6 lines

Quoted 3 lines

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Please note that this patch was tagged for stable 3.18+.

Correct. That's because:

Quoted 4 lines

Quoted 4 lines

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.

This was added much earlier and fixes a real bug in various places.

Quoted 7 lines

Quoted 7 lines

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.

The above wasn't added till 3.18, which warns when the trace event is not enabled. With the backported patch, it now triggers false warnings. But the false warnings wont exist before 3.18.

It doesn't hurt to backport this patch further, it's just not necessary, unless 3a630178fd5f3 was backported too. Was it?

-- Steve

Thanks for clarifying, Steve. I don't think commit 3a630178fd5f3 has been backport to stable kernels, so if you're saying it doesn't hurt to backport dc17147de328 I guess that's up to the stable maintainers to include it or not. Thanks!