rcu: Remove rcu_needs_cpu_flush() to avoid false quiescent states

The purpose of rcu_needs_cpu_flush() was to iterate on pushing the current grace period in order to help the current CPU enter dyntick-idle mode. However, this can result in failures if the CPU starts entering dyntick-idle mode, but then backs out. In this case, the call to rcu_pending() from rcu_needs_cpu_flush() might end up announcing a non-existing quiescent state. This commit therefore removes rcu_needs_cpu_flush() in favor of letting the dyntick-idle machinery at the end of the softirq handler push the loop along via its call to rcu_pending(). Signed-off-by: Paul E. McKenney <[email protected]>
twell · Sep 29, 2011 · e90c53d · e90c53d
1 parent 5b61b0b
commit e90c53d
Show file tree

Hide file tree

Showing 3 changed files with 0 additions and 29 deletions.
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
@@ -1528,9 +1528,6 @@ static void rcu_process_callbacks(struct softirq_action *unused)
 				&__get_cpu_var(rcu_sched_data));
 	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
 	rcu_preempt_process_callbacks();
-
-	/* If we are last CPU on way to dyntick-idle mode, accelerate it. */
-	rcu_needs_cpu_flush();
 	trace_rcu_utilization("End RCU core");
 }
 

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
@@ -458,7 +458,6 @@ static int rcu_preempt_needs_cpu(int cpu);
 static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
 static void rcu_preempt_send_cbs_to_online(void);
 static void __init __rcu_init_preempt(void);
-static void rcu_needs_cpu_flush(void);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static void invoke_rcu_callbacks_kthread(void);

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
@@ -1948,15 +1948,6 @@ int rcu_needs_cpu(int cpu)
 	return rcu_needs_cpu_quick_check(cpu);
 }
 
-/*
- * Check to see if we need to continue a callback-flush operations to
- * allow the last CPU to enter dyntick-idle mode.  But fast dyntick-idle
- * entry is not configured, so we never do need to.
- */
-static void rcu_needs_cpu_flush(void)
-{
-}
-
 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
 
 #define RCU_NEEDS_CPU_FLUSHES 5
@@ -2032,20 +2023,4 @@ int rcu_needs_cpu(int cpu)
 	return c;
 }
 
-/*
- * Check to see if we need to continue a callback-flush operations to
- * allow the last CPU to enter dyntick-idle mode.
- */
-static void rcu_needs_cpu_flush(void)
-{
-	int cpu = smp_processor_id();
-	unsigned long flags;
-
-	if (per_cpu(rcu_dyntick_drain, cpu) <= 0)
-		return;
-	local_irq_save(flags);
-	(void)rcu_needs_cpu(cpu);
-	local_irq_restore(flags);
-}
-
 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */