error if extra rcu_read_lock is added for testing.

	I'm using the PREEMPT_ACTIVE flag to indicate
that we are already under lock. It should work because
__might_sleep is not called with such bit. I also tried to
add new flag in include/linux/hardirq.h but PREEMPT_ACTIVE
depends on the arch, so this alternative looked difficult to
implement.

 include/linux/rcupdate.h |    7 ++++---
 include/linux/sched.h    |   14 ++++++++++++++
 kernel/sched/core.c      |   20 ++++++++++++++++++--
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b758ce1..b594759 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h

@@ -480,9 +480,10 @@ static inline void rcu_preempt_sleep_check(void)
 }
 #endif /* #else #ifdef CONFIG_PROVE_RCU */

-#define rcu_sleep_check()						\
+#define rcu_sleep_check(locked)						\
 	do {								\
-		rcu_preempt_sleep_check();				\
+		if (!(locked))						\
+			rcu_preempt_sleep_check();			\
 		rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),	\
 				   "Illegal context switch in RCU-bh"	\
 				   " read-side critical section");	\

@@ -494,7 +495,7 @@ static inline void rcu_preempt_sleep_check(void)
 #else /* #ifdef CONFIG_PROVE_RCU */

 #define rcu_lockdep_assert(c, s) do { } while (0)
-#define rcu_sleep_check() do { } while (0)
+#define rcu_sleep_check(locked) do { } while (0)

 #endif /* #else #ifdef CONFIG_PROVE_RCU */

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e692a02..027deea 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -2608,6 +2608,20 @@ extern int __cond_resched_softirq(void);
 	__cond_resched_softirq();					\
 })

+#ifdef CONFIG_PREEMPT_RCU
+#define PREEMPT_RCU_OFFSET	1
+#else
+#define PREEMPT_RCU_OFFSET	PREEMPT_CHECK_OFFSET
+#endif
+
+extern int __cond_resched_rcu(void);
+
+#define cond_resched_rcu() ({					\
+	__might_sleep(__FILE__, __LINE__, PREEMPT_ACTIVE |	\
+					  PREEMPT_RCU_OFFSET);	\
+	__cond_resched_rcu();					\
+})
+
 /*
  * Does a critical section need to be broken due to another
  * task waiting?: (technically does not depend on CONFIG_PREEMPT,

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 67d0465..2724be7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c

@@ -2793,7 +2793,7 @@ static inline void schedule_debug(struct task_struct *prev)
 	 */
 	if (unlikely(in_atomic_preempt_off() && !prev->exit_state))
 		__schedule_bug(prev);
-	rcu_sleep_check();
+	rcu_sleep_check(0);

 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));

@@ -4364,6 +4364,20 @@ int __sched __cond_resched_softirq(void)
 }
 EXPORT_SYMBOL(__cond_resched_softirq);

+int __sched __cond_resched_rcu(void)
+{
+#ifndef CONFIG_PREEMPT_RCU
+	if (should_resched()) {
+		rcu_read_unlock();
+		__cond_resched();
+		rcu_read_lock();
+		return 1;
+	}
+#endif
+	return 0;
+}
+EXPORT_SYMBOL(__cond_resched_rcu);
+
 /**
  * yield - yield the current processor to other threads.
  *

@@ -7062,7 +7076,9 @@ void __might_sleep(const char *file, int line, int preempt_offset)
 {
 	static unsigned long prev_jiffy;	/* ratelimiting */

-	rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
+	/* WARN_ON_ONCE() by default, no rate limit reqd. */
+	rcu_sleep_check(preempt_offset & PREEMPT_ACTIVE);