From: Dave Hansen <dave.han...@linux.intel.com>
Dave Jones reported seeing a bug from one of my TLB tracepoints:
http://lkml.kernel.org/r/20140806181801.ga4...@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.
Signed-off-by: Dave Hansen <dave.han...@linux.intel.com>
Cc: Dave Jones <da...@redhat.com>,
Cc: paul...@linux.vnet.ibm.com
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Ingo Molnar <mi...@redhat.com>
---
b/include/linux/tracepoint.h | 11 +++++++++++
1 file changed, 11 insertions(+)
diff -puN include/linux/tracepoint.h~easier-rcu-splat include/linux/tracepoint.h
--- a/include/linux/tracepoint.h~easier-rcu-splat 2014-08-07
10:29:32.701217956 -0700
+++ b/include/linux/tracepoint.h 2014-08-07 10:40:35.244627014 -0700
@@ -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)) \
_
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