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Message-ID: <20120904230834.GB11494@jtriplet-mobl1>
Date: Tue, 4 Sep 2012 16:08:34 -0700
From: Josh Triplett <josh@...htriplett.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
Valdis.Kletnieks@...edu, dhowells@...hat.com,
eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
sbw@....edu, patches@...aro.org,
"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used
from interrupt context
On Tue, Sep 04, 2012 at 06:51:22PM -0400, Steven Rostedt wrote:
> On Tue, 2012-09-04 at 15:33 -0700, Paul E. McKenney wrote:
> > On Fri, Aug 31, 2012 at 11:00:52AM -0700, Josh Triplett wrote:
> > > On Thu, Aug 30, 2012 at 11:56:17AM -0700, Paul E. McKenney wrote:
> > > > From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> > > >
> > > > There is a need to use RCU from interrupt context, but either before
> > > > rcu_irq_enter() is called or after rcu_irq_exit() is called. If the
> > > > interrupt occurs from idle, then lockdep-RCU will complain about such
> > > > uses, as they appear to be illegal uses of RCU from the idle loop.
> > > > In other environments, RCU_NONIDLE() could be used to properly protect
> > > > the use of RCU, but RCU_NONIDLE() currently cannot be invoked except
> > > > from process context.
> > > >
> > > > This commit therefore modifies RCU_NONIDLE() to permit its use more
> > > > globally.
> > > >
> > > > Reported-by: Steven Rostedt <rostedt@...dmis.org>
> > > > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > >
> > > Something seems wrong about this. The addition of EXPORT_SYMBOL_GPL
> > > suggests that such interrupt handlers might live in modules. In what
> > > situation might a module interrupt handler get called from the idle
> > > loop, before rcu_irq_enter or after rcu_irq_exit, and need to know that
> > > when using RCU?
> >
> > Drivers can be in modules, in which case their interrupt handlers will
> > also be in the corresponding module. I do agree that in most cases,
> > the irq_enter() and irq_exit() hooks would be invoked by non-module code,
> > but I do believe that I had to add those exports due to build failures.
> >
> > Steven will let me know if I am confused on this point.
> >
>
> You're not confused, the situation is confusing :-/
>
> Because some trace events happen inside the idle loop after rcu has
> "shutdown", we needed to create "trace_foo_rcuidle()" handlers that can
> handle this condition. That is, for every trace_foo() static inline
> (used at the tracepoint location), there exists a static inline
> trace_foo_rcuidle(), that looks something like this:
>
> static inline void trace_##name##_rcuidle(proto) {
> if (static_key_false(&__tracepoint_##name.key)) {
> rcu_idle_exit();
> __DO_TRACE();
> rcu_idle_enter();
> }
> }
>
> Although these calls are never used by module code, because they are
> static inlines, they are still defined for all tracepoints, kernel
> tracepoints as well as module tracepoints. And thus, need the export :-(
Fair enough.
What about having the tracepoint code generation detect when building as
part of a module via defined(MODULE), and omit the unused _rcuidle
versions in those cases? That would avoid the need to export those
functions at all. Strawman patch (not tested):
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 802de56..41e1ef2 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -136,6 +136,22 @@ static inline void tracepoint_synchronize_unregister(void)
postrcu; \
} while (0)
+#ifdef MODULE
+#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
+ static inline void trace_##name##_rcuidle(proto) \
+ { \
+ if (static_key_false(&__tracepoint_##name.key)) \
+ __DO_TRACE(&__tracepoint_##name, \
+ TP_PROTO(data_proto), \
+ TP_ARGS(data_args), \
+ TP_CONDITION(cond), \
+ rcu_idle_exit(), \
+ rcu_idle_enter()); \
+ }
+#else
+#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)
+#endif
+
/*
* Make sure the alignment of the structure in the __tracepoints section will
* not add unwanted padding between the beginning of the section and the
@@ -151,16 +167,7 @@ static inline void tracepoint_synchronize_unregister(void)
TP_ARGS(data_args), \
TP_CONDITION(cond),,); \
} \
- static inline void trace_##name##_rcuidle(proto) \
- { \
- if (static_key_false(&__tracepoint_##name.key)) \
- __DO_TRACE(&__tracepoint_##name, \
- TP_PROTO(data_proto), \
- TP_ARGS(data_args), \
- TP_CONDITION(cond), \
- rcu_idle_exit(), \
- rcu_idle_enter()); \
- } \
+ __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
static inline int \
register_trace_##name(void (*probe)(data_proto), void *data) \
{ \
If that doesn't work out, please consider adding an explicit comment
saying why you exported the functions.
- Josh Triplett
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