Hi,
On Sun, Jun 26, 2016 at 02:55:48PM -0700, Andy Lutomirski wrote:
> 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.
I've been considering how we'd implement this for arm64, and I suspect
that we'll also need to fold our preempt_count into task_struct
(following from the style of asm-generic/preempt.h).
As far as I can see, we can't make our preempt-count a percpu variable
as with x86, as our percpu ops themselves are based on disabling
preemption.
To that end, would it be possible to keep the thread_info definition per
arch, even with CONFIG_THREAD_INFO_IN_TASK?
Thanks,
Mark.
>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
> include/linux/init_task.h | 9 +++++++++
> include/linux/sched.h | 36 ++++++++++++++++++++++++++++++++++--
> include/linux/thread_info.h | 15 +++++++++++++++
> init/Kconfig | 3 +++
> init/init_task.c | 7 +++++--
> kernel/sched/sched.h | 4 ++++
> 6 files changed, 70 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/init_task.h b/include/linux/init_task.h
> index f8834f820ec2..9c04d44eeb3c 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 569df670407a..4108b4880b86 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1456,6 +1456,13 @@ 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;
> @@ -1465,6 +1472,9 @@ 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;
> @@ -2557,7 +2567,9 @@ 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)];
> };
>
> @@ -3045,10 +3057,26 @@ 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)
> {
> @@ -3348,7 +3376,11 @@ 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 352b1542f5cc..b2b32d63bc8e 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 f755a602d4a1..0c83af6d3753 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -26,6 +26,9 @@ config IRQ_WORK
> config BUILDTIME_EXTABLE_SORT
> bool
>
> +config THREAD_INFO_IN_TASK
> + bool
> +
> menu "General setup"
>
> config BROKEN
> diff --git a/init/init_task.c b/init/init_task.c
> index ba0a7f362d9e..11f83be1fa79 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 7cbeb92a1cb9..a1cabcea4c54 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -999,7 +999,11 @@ 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
> }
> --
> 2.7.4
>
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