From: Paul E. McKenney <paul.mckenney@linaro.org>
Date: Tue, 31 Jul 2012 17:12:48 +0000 (-0700)
Subject: rcu: Permit RCU_NONIDLE() to be used from interrupt context
X-Git-Tag: next-20120907~29^2~2^3~11
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=5dc57c8027996da5248c8e2d6c1d854cf88ca86d;p=karo-tx-linux.git

rcu: Permit RCU_NONIDLE() to be used from interrupt context

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.

It also exports rcu_irq_exit() and rcu_irq_enter() in order to avoid
build errors.  The need for this is a bit counter-intuitive, hence this
explanation from Steven Rostedt:

	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 :-(

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>
---

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 115ead2b5155..0fbbd52e01f9 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -210,14 +210,12 @@ extern void exit_rcu(void);
  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
  * quite limited.  If deeper nesting is required, it will be necessary
  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
- *
- * This macro may be used from process-level code only.
  */
 #define RCU_NONIDLE(a) \
 	do { \
-		rcu_idle_exit(); \
+		rcu_irq_enter(); \
 		do { a; } while (0); \
-		rcu_idle_enter(); \
+		rcu_irq_exit(); \
 	} while (0)
 
 /*
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index e4163c5af1de..2e073a24d250 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -115,6 +115,7 @@ void rcu_irq_exit(void)
 	rcu_idle_enter_common(newval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_irq_exit);
 
 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 static void rcu_idle_exit_common(long long oldval)
@@ -172,6 +173,7 @@ void rcu_irq_enter(void)
 	rcu_idle_exit_common(oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_irq_enter);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f280e542e3e9..96b8aff433a9 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -447,6 +447,7 @@ void rcu_irq_exit(void)
 		rcu_idle_enter_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_irq_exit);
 
 /*
  * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
@@ -542,6 +543,7 @@ void rcu_irq_enter(void)
 		rcu_idle_exit_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_irq_enter);
 
 /**
  * rcu_nmi_enter - inform RCU of entry to NMI context