Re: [PATCH 1/2 v2] rcu,cleanup: move synchronize_sched_expedited() out of sched.c

[Lai Jiangshan <laijs@cn.fujitsu.com>]

On 10/21/2010 08:19 AM, Paul E. McKenney wrote:
> On Wed, Oct 20, 2010 at 12:15:12PM -0700, Paul E. McKenney wrote:
>> On Wed, Oct 20, 2010 at 02:12:58PM +0800, Lai Jiangshan wrote:
>>> The first version of synchronize_sched_expedited() use the migration code
>>> of the scheduler code, so it have to be implemented in sched.c
>>>
>>> but now, the synchronize_sched_expedited() does not use such code,
>>> it is time to move it out of sched.c.
>>>
>>> Different rcu implementation' synchronize_sched_expedited() are also
>>> different. so we move synchronize_sched_expedited() to kernel/rcutree_plugin.h
>>> or include/linux/rcutiny.h instead of kerenl/rcupdate.c
>>
>> Queued, thank you!!!
> 
> Hello again, Lai,
> 
> I hit the following build error during testing:
> 
> kernel/built-in.o: In function `.synchronize_rcu_expedited':
> (.text+0x787d8): undefined reference to `.synchronize_sched_expedited'
> kernel/built-in.o:(.toc1+0x1fe0): undefined reference to `synchronize_sched_expedited'
> 
> This build uses defconfig with the following applied:
> 
> CONFIG_RCU_TRACE=y
> CONFIG_RCU_FAST_NO_HZ=y
> CONFIG_NO_HZ=y
> CONFIG_RCU_CPU_STALL_DETECTOR=y
> CONFIG_SMP=y
> CONFIG_RCU_FANOUT=8
> CONFIG_NR_CPUS=8
> CONFIG_RCU_FANOUT_EXACT=n
> CONFIG_HOTPLUG_CPU=y
> CONFIG_PREEMPT_NONE=y
> CONFIG_PREEMPT_VOLUNTARY=n
> CONFIG_PREEMPT=n
> CONFIG_TREE_RCU=y
> CONFIG_TREE_PREEMPT_RCU=n
> CONFIG_RCU_TORTURE_TEST=m
> CONFIG_MODULE_UNLOAD=y
> CONFIG_SYSFS_DEPRECATED_V2=y
> CONFIG_IKCONFIG=y
> CONFIG_IKCONFIG_PROC=y
> 
> Thoughts?
> 
> 							Thanx, Paul
> 
> 

I moved the code into CONFIG_TREE_PREEMPT_RCU=y codes. fixed version:


Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0d0b640..ead36da 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -66,7 +66,6 @@ extern void call_rcu_sched(struct rcu_head *head,
 extern void synchronize_sched(void);
 extern void rcu_barrier_bh(void);
 extern void rcu_barrier_sched(void);
-extern void synchronize_sched_expedited(void);
 extern int sched_expedited_torture_stats(char *page);
 
 static inline void __rcu_read_lock_bh(void)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 13877cb..4d84452 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -58,6 +58,11 @@ static inline void synchronize_rcu_bh_expedited(void)
 	synchronize_sched();
 }
 
+static inline void synchronize_sched_expedited(void)
+{
+	synchronize_sched();
+}
+
 #ifdef CONFIG_TINY_RCU
 
 static inline void rcu_preempt_note_context_switch(void)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 95518e6..9a1fd6c 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -47,6 +47,7 @@ static inline void exit_rcu(void)
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 extern void synchronize_rcu_bh(void);
+extern void synchronize_sched_expedited(void);
 extern void synchronize_rcu_expedited(void);
 
 static inline void synchronize_rcu_bh_expedited(void)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 0e75d60..0de359b 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -25,6 +25,7 @@
  */
 
 #include <linux/delay.h>
+#include <linux/stop_machine.h>
 
 /*
  * Check the RCU kernel configuration parameters and print informative
@@ -1014,6 +1015,76 @@ static void __init __rcu_init_preempt(void)
 
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
+#ifndef CONFIG_SMP
+
+void synchronize_sched_expedited(void)
+{
+	cond_resched();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#else /* #ifndef CONFIG_SMP */
+
+static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0);
+
+static int synchronize_sched_expedited_cpu_stop(void *data)
+{
+	/*
+	 * There must be a full memory barrier on each affected CPU
+	 * between the time that try_stop_cpus() is called and the
+	 * time that it returns.
+	 *
+	 * In the current initial implementation of cpu_stop, the
+	 * above condition is already met when the control reaches
+	 * this point and the following smp_mb() is not strictly
+	 * necessary.  Do smp_mb() anyway for documentation and
+	 * robustness against future implementation changes.
+	 */
+	smp_mb(); /* See above comment block. */
+	return 0;
+}
+
+/*
+ * Wait for an rcu-sched grace period to elapse, but use "big hammer"
+ * approach to force grace period to end quickly.  This consumes
+ * significant time on all CPUs, and is thus not recommended for
+ * any sort of common-case code.
+ *
+ * Note that it is illegal to call this function while holding any
+ * lock that is acquired by a CPU-hotplug notifier.  Failing to
+ * observe this restriction will result in deadlock.
+ */
+void synchronize_sched_expedited(void)
+{
+	int snap, trycount = 0;
+
+	smp_mb();  /* ensure prior mod happens before capturing snap. */
+	snap = atomic_read(&synchronize_sched_expedited_count) + 1;
+	get_online_cpus();
+	while (try_stop_cpus(cpu_online_mask,
+			     synchronize_sched_expedited_cpu_stop,
+			     NULL) == -EAGAIN) {
+		put_online_cpus();
+		if (trycount++ < 10)
+			udelay(trycount * num_online_cpus());
+		else {
+			synchronize_sched();
+			return;
+		}
+		if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {
+			smp_mb(); /* ensure test happens before caller kfree */
+			return;
+		}
+		get_online_cpus();
+	}
+	atomic_inc(&synchronize_sched_expedited_count);
+	smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */
+	put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#endif /* #else #ifndef CONFIG_SMP */
+
 #if !defined(CONFIG_RCU_FAST_NO_HZ)
 
 /*
diff --git a/kernel/sched.c b/kernel/sched.c
index abf8440..9dc7775 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9332,72 +9332,3 @@ struct cgroup_subsys cpuacct_subsys = {
 };
 #endif	/* CONFIG_CGROUP_CPUACCT */
 
-#ifndef CONFIG_SMP
-
-void synchronize_sched_expedited(void)
-{
-	barrier();
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
-#else /* #ifndef CONFIG_SMP */
-
-static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0);
-
-static int synchronize_sched_expedited_cpu_stop(void *data)
-{
-	/*
-	 * There must be a full memory barrier on each affected CPU
-	 * between the time that try_stop_cpus() is called and the
-	 * time that it returns.
-	 *
-	 * In the current initial implementation of cpu_stop, the
-	 * above condition is already met when the control reaches
-	 * this point and the following smp_mb() is not strictly
-	 * necessary.  Do smp_mb() anyway for documentation and
-	 * robustness against future implementation changes.
-	 */
-	smp_mb(); /* See above comment block. */
-	return 0;
-}
-
-/*
- * Wait for an rcu-sched grace period to elapse, but use "big hammer"
- * approach to force grace period to end quickly.  This consumes
- * significant time on all CPUs, and is thus not recommended for
- * any sort of common-case code.
- *
- * Note that it is illegal to call this function while holding any
- * lock that is acquired by a CPU-hotplug notifier.  Failing to
- * observe this restriction will result in deadlock.
- */
-void synchronize_sched_expedited(void)
-{
-	int snap, trycount = 0;
-
-	smp_mb();  /* ensure prior mod happens before capturing snap. */
-	snap = atomic_read(&synchronize_sched_expedited_count) + 1;
-	get_online_cpus();
-	while (try_stop_cpus(cpu_online_mask,
-			     synchronize_sched_expedited_cpu_stop,
-			     NULL) == -EAGAIN) {
-		put_online_cpus();
-		if (trycount++ < 10)
-			udelay(trycount * num_online_cpus());
-		else {
-			synchronize_sched();
-			return;
-		}
-		if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {
-			smp_mb(); /* ensure test happens before caller kfree */
-			return;
-		}
-		get_online_cpus();
-	}
-	atomic_inc(&synchronize_sched_expedited_count);
-	smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */
-	put_online_cpus();
-}
-EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
-
-#endif /* #else #ifndef CONFIG_SMP */