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    Subject[tip:x86/asm] sched/core: Allow putting thread_info into task_struct
    Commit-ID:  c65eacbe290b8141554c71b2c94489e73ade8c8d
    Gitweb: http://git.kernel.org/tip/c65eacbe290b8141554c71b2c94489e73ade8c8d
    Author: Andy Lutomirski <luto@kernel.org>
    AuthorDate: Tue, 13 Sep 2016 14:29:24 -0700
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 15 Sep 2016 08:25:13 +0200

    sched/core: Allow putting thread_info into task_struct

    If an arch opts in by setting CONFIG_THREAD_INFO_IN_TASK_STRUCT,
    then thread_info is defined as a single 'u32 flags' and is the first
    entry of task_struct. thread_info::task is removed (it serves no
    purpose if thread_info is embedded in task_struct), and
    thread_info::cpu gets its own slot in task_struct.

    This is heavily based on a patch written by Linus.

    Originally-from: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Jann Horn <jann@thejh.net>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/a0898196f0476195ca02713691a5037a14f2aac5.1473801993.git.luto@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    include/linux/init_task.h | 9 +++++++++
    include/linux/sched.h | 36 ++++++++++++++++++++++++++++++++++--
    include/linux/thread_info.h | 15 +++++++++++++++
    init/Kconfig | 7 +++++++
    init/init_task.c | 7 +++++--
    kernel/sched/sched.h | 4 ++++
    6 files changed, 74 insertions(+), 4 deletions(-)

    diff --git a/include/linux/init_task.h b/include/linux/init_task.h
    index f8834f8..9c04d44 100644
    --- a/include/linux/init_task.h
    +++ b/include/linux/init_task.h
    @@ -15,6 +15,8 @@
    #include <net/net_namespace.h>
    #include <linux/sched/rt.h>

    +#include <asm/thread_info.h>
    +
    #ifdef CONFIG_SMP
    # define INIT_PUSHABLE_TASKS(tsk) \
    .pushable_tasks = PLIST_NODE_INIT(tsk.pushable_tasks, MAX_PRIO),
    @@ -183,12 +185,19 @@ extern struct task_group root_task_group;
    # define INIT_KASAN(tsk)
    #endif

    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    +# define INIT_TASK_TI(tsk) .thread_info = INIT_THREAD_INFO(tsk),
    +#else
    +# define INIT_TASK_TI(tsk)
    +#endif
    +
    /*
    * INIT_TASK is used to set up the first task table, touch at
    * your own risk!. Base=0, limit=0x1fffff (=2MB)
    */
    #define INIT_TASK(tsk) \
    { \
    + INIT_TASK_TI(tsk) \
    .state = 0, \
    .stack = init_stack, \
    .usage = ATOMIC_INIT(2), \
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 20f9f47..a287e8b 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1458,6 +1458,13 @@ struct tlbflush_unmap_batch {
    };

    struct task_struct {
    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    + /*
    + * For reasons of header soup (see current_thread_info()), this
    + * must be the first element of task_struct.
    + */
    + struct thread_info thread_info;
    +#endif
    volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
    void *stack;
    atomic_t usage;
    @@ -1467,6 +1474,9 @@ struct task_struct {
    #ifdef CONFIG_SMP
    struct llist_node wake_entry;
    int on_cpu;
    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    + unsigned int cpu; /* current CPU */
    +#endif
    unsigned int wakee_flips;
    unsigned long wakee_flip_decay_ts;
    struct task_struct *last_wakee;
    @@ -2588,7 +2598,9 @@ extern void set_curr_task(int cpu, struct task_struct *p);
    void yield(void);

    union thread_union {
    +#ifndef CONFIG_THREAD_INFO_IN_TASK
    struct thread_info thread_info;
    +#endif
    unsigned long stack[THREAD_SIZE/sizeof(long)];
    };

    @@ -3076,10 +3088,26 @@ static inline void threadgroup_change_end(struct task_struct *tsk)
    cgroup_threadgroup_change_end(tsk);
    }

    -#ifndef __HAVE_THREAD_FUNCTIONS
    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    +
    +static inline struct thread_info *task_thread_info(struct task_struct *task)
    +{
    + return &task->thread_info;
    +}
    +static inline void *task_stack_page(const struct task_struct *task)
    +{
    + return task->stack;
    +}
    +#define setup_thread_stack(new,old) do { } while(0)
    +static inline unsigned long *end_of_stack(const struct task_struct *task)
    +{
    + return task->stack;
    +}
    +
    +#elif !defined(__HAVE_THREAD_FUNCTIONS)

    #define task_thread_info(task) ((struct thread_info *)(task)->stack)
    -#define task_stack_page(task) ((task)->stack)
    +#define task_stack_page(task) ((void *)(task)->stack)

    static inline void setup_thread_stack(struct task_struct *p, struct task_struct *org)
    {
    @@ -3379,7 +3407,11 @@ static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)

    static inline unsigned int task_cpu(const struct task_struct *p)
    {
    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    + return p->cpu;
    +#else
    return task_thread_info(p)->cpu;
    +#endif
    }

    static inline int task_node(const struct task_struct *p)
    diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
    index 2b5b10e..e2d0fd8 100644
    --- a/include/linux/thread_info.h
    +++ b/include/linux/thread_info.h
    @@ -13,6 +13,21 @@
    struct timespec;
    struct compat_timespec;

    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    +struct thread_info {
    + u32 flags; /* low level flags */
    +};
    +
    +#define INIT_THREAD_INFO(tsk) \
    +{ \
    + .flags = 0, \
    +}
    +#endif
    +
    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    +#define current_thread_info() ((struct thread_info *)current)
    +#endif
    +
    /*
    * System call restart block.
    */
    diff --git a/init/Kconfig b/init/Kconfig
    index cac3f09..ec8d438 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -26,6 +26,13 @@ config IRQ_WORK
    config BUILDTIME_EXTABLE_SORT
    bool

    +config THREAD_INFO_IN_TASK
    + bool
    + help
    + Select this to move thread_info off the stack into task_struct. To
    + make this work, an arch will need to remove all thread_info fields
    + except flags and fix any runtime bugs.
    +
    menu "General setup"

    config BROKEN
    diff --git a/init/init_task.c b/init/init_task.c
    index ba0a7f36..11f83be1 100644
    --- a/init/init_task.c
    +++ b/init/init_task.c
    @@ -22,5 +22,8 @@ EXPORT_SYMBOL(init_task);
    * Initial thread structure. Alignment of this is handled by a special
    * linker map entry.
    */
    -union thread_union init_thread_union __init_task_data =
    - { INIT_THREAD_INFO(init_task) };
    +union thread_union init_thread_union __init_task_data = {
    +#ifndef CONFIG_THREAD_INFO_IN_TASK
    + INIT_THREAD_INFO(init_task)
    +#endif
    +};
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index c64fc51..3655c96 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -1000,7 +1000,11 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
    * per-task data have been completed by this moment.
    */
    smp_wmb();
    +#ifdef CONFIG_THREAD_INFO_IN_TASK
    + p->cpu = cpu;
    +#else
    task_thread_info(p)->cpu = cpu;
    +#endif
    p->wake_cpu = cpu;
    #endif
    }
    \
     
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