Commit 3a630178 authored Aug 07, 2014 by Dave Hansen Committed by Steven Rostedt Sep 10, 2014

tracing: generate RCU warnings even when tracepoints are disabled

Dave Jones reported seeing a bug from one of my TLB tracepoints:

	http://lkml.kernel.org/r/20140806181801.GA4605@redhat.com

I've been running these patches for months and never saw this.
But, a big chunk of my testing, especially with all the debugging
enabled, was in a vm where intel_idle doesn't work.  On the
systems where I was using intel_idle, I never had lockdep enabled
and this tracepoint on at the same time.

This patch ensures that whenever we have lockdep available, we do
_some_ RCU activity at the site of the tracepoint, despite
whether the tracepoint's condition matches or even if the
tracepoint itself is completely disabled.  This is a bit of a
hack, but it is pretty self-contained.

I confirmed that with this patch plus lockdep I get the same
splat as Dave Jones did, but without enabling the tracepoint
explicitly.

Link: http://lkml.kernel.org/p/20140807175204.C257CAC5@viggo.jf.intel.com



Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Dave Jones <davej@redhat.com>,
Cc: paulmck@linux.vnet.ibm.com
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent fef5aeee

include/linux/tracepoint.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -157,6 +157,12 @@ extern void syscall_unregfunc(void);
		* Make sure the alignment of the structure in the __tracepoints section will
		* not add unwanted padding between the beginning of the section and the
		* structure. Force alignment to the same alignment as the section start.
		*
		* When lockdep is enabled, we make sure to always do the RCU portions of
		* the tracepoint code, regardless of whether tracing is on or we match the
		* condition. This lets us find RCU issues triggered with tracepoints even
		* when this tracepoint is off. This code has no purpose other than poking
		* RCU a bit.
		*/
		#define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
		extern struct tracepoint __tracepoint_##name; \
		@@ -167,6 +173,11 @@ extern void syscall_unregfunc(void);
		TP_PROTO(data_proto), \
		TP_ARGS(data_args), \
		TP_CONDITION(cond),,); \
		if (IS_ENABLED(CONFIG_LOCKDEP)) { \
		rcu_read_lock_sched_notrace(); \
		rcu_dereference_sched(__tracepoint_##name.funcs);\
		rcu_read_unlock_sched_notrace(); \
		} \
		} \
		__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \
		PARAMS(cond), PARAMS(data_proto), PARAMS(data_args)) \