[RFC PATCH 4/5] RCU: Add TASK_RCU_OFFSET

[Lai Jiangshan]

We can not include linux/sched.h in linux/rcupdate.h.
If we access task's task_rcu_strut without linux/sched.h included,
We will failed with compiling error.

So we add TASK_RCU_OFFSET, which help us access
task's task_rcu_strut without linux/sched.h included.
Now, task_rcu_struct(), current_task_rcu_struct(), task_of_task_rcu() and
rcu_copy_process() can be used anywhere without linux/sched.h included.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
 include/linux/rcupdate.h |   49 +++++++++++++++++++++++++++++++++++++++++----
 kernel/kernel-offsets.c  |    3 ++
 2 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 3500138..a5ed3fe 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -140,11 +140,50 @@ static inline void init_task_rcu_struct(struct task_rcu_struct *task_rcu)
 #endif
 }
 
-#define task_rcu_struct(t) (&(t)->task_rcu_struct)
-#define current_task_rcu_struct() task_rcu_struct(current)
-#define task_of_task_rcu(task_rcu) container_of(task_rcu, struct task_struct,\
-				   task_rcu_struct)
-#define rcu_copy_process(tsk) init_task_rcu_struct(task_rcu_struct(tsk))
+#ifdef __KBUILD_GENARATING__
+/*
+ * Very eary kbuild stage, many important defines including TASK_RCU_OFFSET
+ * are not available, use dummies to avoid compiling errors.
+ */
+static inline
+struct task_rcu_struct *task_rcu_struct(struct task_struct *t)
+{
+	(void)t;
+	return (struct task_rcu_struct *)0x3L;
+}
+
+static inline
+struct task_struct *task_of_task_rcu(struct task_rcu_struct *task_rcu)
+{
+	(void)task_rcu;
+	return (struct task_struct *)-0x3L;
+}
+#else
+/* for generated TASK_RCU_OFFSET */
+#include <generated/kernel-offsets.h>
+
+static inline
+struct task_rcu_struct *task_rcu_struct(struct task_struct *t)
+{
+	return (struct task_rcu_struct *)(((void *)t) + TASK_RCU_OFFSET);
+}
+
+static inline
+struct task_struct *task_of_task_rcu(struct task_rcu_struct *task_rcu)
+{
+	return (struct task_struct *)(((void *)task_rcu) - TASK_RCU_OFFSET);
+}
+#endif
+
+static inline struct task_rcu_struct *current_task_rcu_struct(void)
+{
+	return task_rcu_struct(current);
+}
+
+static inline void rcu_copy_process(struct task_struct *tsk)
+{
+	init_task_rcu_struct(task_rcu_struct(tsk));
+}
 
 #ifdef CONFIG_PREEMPT_RCU
 
diff --git a/kernel/kernel-offsets.c b/kernel/kernel-offsets.c
index fb73ccf..a890511 100644
--- a/kernel/kernel-offsets.c
+++ b/kernel/kernel-offsets.c
@@ -4,11 +4,14 @@
  * Copyright (C) 2010 Lai Jiangshan
  */
 
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
 #include <linux/kbuild.h>
 
 void foo(void);
 
 void foo(void)
 {
+	OFFSET(TASK_RCU_OFFSET, task_struct, task_rcu_struct);
 }
 
-- 
1.7.4

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