Merge branch 'urgent.2014.06.23a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/urgent

Pull RCU fixes from Paul E. McKenney:

" This series includes the following:

   1.    Export a pair of debug-object interfaces for RCU that will
         allow the slab allocators to avoid a recursion bug located
         by Sasha Levin.  Strictly speaking, this is not a regression,
         but it would be good to enable the fix.

   2.    Address a serious performance regression on an open/close
         micro-benchmark located by Dave Hansen.  The offending commit
         is ac1bea85781e (Make cond_resched() report RCU quiescent states).  "

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 10 insertions, 36 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 5a75d19aa661..6a94cc8b1ca0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -44,7 +44,6 @@
 #include <linux/debugobjects.h>
 #include <linux/bug.h>
 #include <linux/compiler.h>
-#include <linux/percpu.h>
 #include <asm/barrier.h>
 
 extern int rcu_expedited; /* for sysctl */
@@ -300,41 +299,6 @@ bool __rcu_is_watching(void);
 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
 
 /*
- * Hooks for cond_resched() and friends to avoid RCU CPU stall warnings.
- */
-
-#define RCU_COND_RESCHED_LIM 256	/* ms vs. 100s of ms. */
-DECLARE_PER_CPU(int, rcu_cond_resched_count);
-void rcu_resched(void);
-
-/*
- * Is it time to report RCU quiescent states?
- *
- * Note unsynchronized access to rcu_cond_resched_count.  Yes, we might
- * increment some random CPU's count, and possibly also load the result from
- * yet another CPU's count.  We might even clobber some other CPU's attempt
- * to zero its counter.  This is all OK because the goal is not precision,
- * but rather reasonable amortization of rcu_note_context_switch() overhead
- * and extremely high probability of avoiding RCU CPU stall warnings.
- * Note that this function has to be preempted in just the wrong place,
- * many thousands of times in a row, for anything bad to happen.
- */
-static inline bool rcu_should_resched(void)
-{
-	return raw_cpu_inc_return(rcu_cond_resched_count) >=
-	       RCU_COND_RESCHED_LIM;
-}
-
-/*
- * Report quiscent states to RCU if it is time to do so.
- */
-static inline void rcu_cond_resched(void)
-{
-	if (unlikely(rcu_should_resched()))
-		rcu_resched();
-}
-
-/*
  * Infrastructure to implement the synchronize_() primitives in
  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
  */
@@ -358,9 +322,19 @@ void wait_rcu_gp(call_rcu_func_t crf);
  * initialization.
  */
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+void init_rcu_head(struct rcu_head *head);
+void destroy_rcu_head(struct rcu_head *head);
 void init_rcu_head_on_stack(struct rcu_head *head);
 void destroy_rcu_head_on_stack(struct rcu_head *head);
 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+static inline void init_rcu_head(struct rcu_head *head)
+{
+}
+
+static inline void destroy_rcu_head(struct rcu_head *head)
+{
+}
+
 static inline void init_rcu_head_on_stack(struct rcu_head *head)
 {
 }