rcu: move TINY_RCU from softirq to kthread

If RCU priority boosting is to be meaningful, callback invocation must
be boosted in addition to preempted RCU readers.  Otherwise, in presence
of CPU real-time threads, the grace period ends, but the callbacks don't
get invoked.  If the callbacks don't get invoked, the associated memory
doesn't get freed, so the system is still subject to OOM.

But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit
moves the callback invocations to a kthread, which can be boosted easily.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 13877cb93a60..ea025a611fcc 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,7 +27,9 @@
 
 #include <linux/cache.h>
 
-#define rcu_init_sched()        do { } while (0)
+static inline void rcu_init(void)
+{
+}
 
 #ifdef CONFIG_TINY_RCU
 
@@ -125,16 +127,12 @@ static inline void rcu_cpu_stall_reset(void)
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-
 extern int rcu_scheduler_active __read_mostly;
 extern void rcu_scheduler_starting(void);
-
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
 static inline void rcu_scheduler_starting(void)
 {
 }
-
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #endif /* __LINUX_RCUTINY_H */