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    Subject[tip: core/rcu] rcu: Provide __rcu_is_watching()
    The following commit has been merged into the core/rcu branch of tip:

    Commit-ID: b1fcf9b83c4149c63d1e0c699e85f93cbe28e211
    Gitweb: https://git.kernel.org/tip/b1fcf9b83c4149c63d1e0c699e85f93cbe28e211
    Author: Thomas Gleixner <tglx@linutronix.de>
    AuthorDate: Tue, 12 May 2020 09:44:43 +02:00
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitterDate: Tue, 19 May 2020 15:51:21 +02:00

    rcu: Provide __rcu_is_watching()

    Same as rcu_is_watching() but without the preempt_disable/enable() pair
    inside the function. It is merked noinstr so it ends up in the
    non-instrumentable text section.

    This is useful for non-preemptible code especially in the low level entry
    section. Using rcu_is_watching() there results in a call to the
    preempt_schedule_notrace() thunk which triggers noinstr section warnings in
    objtool.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Peter Zijlstra <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20200512213810.518709291@linutronix.de

    ---
    include/linux/rcutiny.h | 1 +
    include/linux/rcutree.h | 1 +
    kernel/rcu/tree.c | 5 +++++
    3 files changed, 7 insertions(+)

    diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
    index 980eb78..c869fb2 100644
    --- a/include/linux/rcutiny.h
    +++ b/include/linux/rcutiny.h
    @@ -86,6 +86,7 @@ static inline void rcu_scheduler_starting(void) { }
    static inline void rcu_end_inkernel_boot(void) { }
    static inline bool rcu_inkernel_boot_has_ended(void) { return true; }
    static inline bool rcu_is_watching(void) { return true; }
    +static inline bool __rcu_is_watching(void) { return true; }
    static inline void rcu_momentary_dyntick_idle(void) { }
    static inline void kfree_rcu_scheduler_running(void) { }
    static inline bool rcu_gp_might_be_stalled(void) { return false; }
    diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
    index 02016e0..9366fa4 100644
    --- a/include/linux/rcutree.h
    +++ b/include/linux/rcutree.h
    @@ -58,6 +58,7 @@ extern int rcu_scheduler_active __read_mostly;
    void rcu_end_inkernel_boot(void);
    bool rcu_inkernel_boot_has_ended(void);
    bool rcu_is_watching(void);
    +bool __rcu_is_watching(void);
    #ifndef CONFIG_PREEMPTION
    void rcu_all_qs(void);
    #endif
    diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    index 62ee012..90c8be2 100644
    --- a/kernel/rcu/tree.c
    +++ b/kernel/rcu/tree.c
    @@ -985,6 +985,11 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
    }
    }

    +noinstr bool __rcu_is_watching(void)
    +{
    + return !rcu_dynticks_curr_cpu_in_eqs();
    +}
    +
    /**
    * rcu_is_watching - see if RCU thinks that the current CPU is not idle
    *
    \
     
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