[PATCH tip/core/rcu 11/20] sched,rcu: Make cond_resched() provide RCU quiescent state

[Paul E. McKenney]

There is some confusion as to which of cond_resched() or
cond_resched_rcu_qs() should be added to long in-kernel loops.
This commit therefore eliminates the decision by adding RCU
quiescent states to cond_resched().

Warning: This is a prototype.  For example, it does not correctly
handle Tasks RCU.  Which is OK for the moment, given that no one
actually uses Tasks RCU yet.

Reported-by: Michal Hocko <mhocko@xxxxxxxxxx>
Not-yet-signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 include/linux/sched.h | 3 ++-
 kernel/sched/core.c   | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4d1905245c7a..1531c48f56e2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3352,10 +3352,11 @@ static inline int signal_pending_state(long state, struct task_struct *p)
  * cond_resched_lock() will drop the spinlock before scheduling,
  * cond_resched_softirq() will enable bhs before scheduling.
  */
+void rcu_all_qs(void);
 #ifndef CONFIG_PREEMPT
 extern int _cond_resched(void);
 #else
-static inline int _cond_resched(void) { return 0; }
+static inline int _cond_resched(void) { rcu_all_qs(); return 0; }
 #endif
 
 #define cond_resched() ({			\
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c56fb57f2991..b442f8918eb9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4907,6 +4907,7 @@ int __sched _cond_resched(void)
 		preempt_schedule_common();
 		return 1;
 	}
+	rcu_all_qs();
 	return 0;
 }
 EXPORT_SYMBOL(_cond_resched);
-- 
2.5.2