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    Subject[RFC PATCH 4/5] RCU: Add TASK_RCU_OFFSET


    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@cn.fujitsu.com>
    ---
    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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