[PATCH 3/4] jrcu: tap might_resched()

[Joe Korty <joe.korty@ccur.com>]

jrcu: tap into might_resched.

All places where the voluntary preemption patches have marked
as safe to context switch are also known rcu quiescent points.

Not fundamentally needed, accelerates rcu batching.

Signed-off-by: Joe Korty <joe.korty@ccur.com>

Index: b/include/linux/kernel.h
===================================================================
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -114,11 +114,18 @@ struct completion;
 struct pt_regs;
 struct user;
 
+/* cannot bring in linux/rcupdate.h at this point */
+#ifdef CONFIG_JRCU
+extern void rcu_note_might_resched(void);
+#else
+#define rcu_note_might_resched()
+#endif /*JRCU */
+
 #ifdef CONFIG_PREEMPT_VOLUNTARY
 extern int _cond_resched(void);
-# define might_resched() _cond_resched()
+# define might_resched() do { _cond_resched(); rcu_note_might_resched(); } while (0)
 #else
-# define might_resched() do { } while (0)
+# define might_resched() do { rcu_note_might_resched(); } while (0)
 #endif
 
 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
Index: b/include/linux/jrcu.h
===================================================================
--- a/include/linux/jrcu.h
+++ b/include/linux/jrcu.h
@@ -71,6 +71,8 @@ extern void rcu_note_context_switch(int 
 #define rcu_sched_qs				rcu_note_context_switch
 #define rcu_bh_qs				rcu_note_context_switch
 
+extern void rcu_note_might_resched(void);
+
 extern void rcu_scheduler_starting(void);
 extern int rcu_scheduler_active __read_mostly;
 
Index: b/kernel/jrcu.c
===================================================================
--- a/kernel/jrcu.c
+++ b/kernel/jrcu.c
@@ -166,6 +166,16 @@ void rcu_note_context_switch(int cpu)
 	rcu_eob(cpu);
 }
 
+void rcu_note_might_resched(void)
+{
+	unsigned long flags;
+
+	raw_local_irq_save(flags);
+	rcu_eob(rcu_cpu());
+	raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL(rcu_note_might_resched);
+
 void rcu_barrier(void)
 {
 	struct rcu_synchronize rcu;