Messages in this thread | | | Date | Tue, 4 Sep 2012 16:14:15 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context |
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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@linaro.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@goodmis.org> > > > > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.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 :-(
Very good -- I will add this to the commit log, with attribution.
Thanx, Paul
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