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    Subject[PATCH v2 2/5] preempt/dynamic: Introduce preempt mode accessors
    Date
    CONFIG_PREEMPT{_NONE, _VOLUNTARY} designate either:
    o The build-time preemption model when !PREEMPT_DYNAMIC
    o The default boot-time preemption model when PREEMPT_DYNAMIC

    IOW, using those on PREEMPT_DYNAMIC kernels is meaningless - the actual
    model could have been set to something else by the "preempt=foo" cmdline
    parameter.

    Introduce a set of helpers to determine the actual preemption mode used by
    the live kernel.

    Suggested-by: Marco Elver <elver@google.com>
    Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
    ---
    include/linux/sched.h | 16 ++++++++++++++++
    kernel/sched/core.c | 11 +++++++++++
    2 files changed, 27 insertions(+)

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 5f8db54226af..0640d5622496 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -2073,6 +2073,22 @@ static inline void cond_resched_rcu(void)
    #endif
    }

    +#ifdef CONFIG_PREEMPT_DYNAMIC
    +
    +extern bool is_preempt_none(void);
    +extern bool is_preempt_voluntary(void);
    +extern bool is_preempt_full(void);
    +
    +#else
    +
    +#define is_preempt_none() IS_ENABLED(CONFIG_PREEMPT_NONE)
    +#define is_preempt_voluntary() IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)
    +#define is_preempt_full() IS_ENABLED(CONFIG_PREEMPT)
    +
    +#endif
    +
    +#define is_preempt_rt() IS_ENABLED(CONFIG_PREEMPT_RT)
    +
    /*
    * Does a critical section need to be broken due to another
    * task waiting?: (technically does not depend on CONFIG_PREEMPTION,
    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 97047aa7b6c2..9db7f77e53c3 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -6638,6 +6638,17 @@ static void __init preempt_dynamic_init(void)
    }
    }

    +#define PREEMPT_MODE_ACCESSOR(mode) \
    + bool is_preempt_##mode(void) \
    + { \
    + WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
    + return preempt_dynamic_mode == preempt_dynamic_##mode; \
    + }
    +
    +PREEMPT_MODE_ACCESSOR(none)
    +PREEMPT_MODE_ACCESSOR(voluntary)
    +PREEMPT_MODE_ACCESSOR(full)
    +
    #else /* !CONFIG_PREEMPT_DYNAMIC */

    static inline void preempt_dynamic_init(void) { }
    --
    2.25.1
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