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    Subject[PATCH RFC tip/core/rcu 08/20] rcu,cleanup: move synchronize_sched_expedited() out of sched.c
    Date
    From: Lai Jiangshan <laijs@cn.fujitsu.com>

    The first version of synchronize_sched_expedited() used the migration
    code in the scheduler, and was therefore implemented in kernel/sched.c.
    However, the more recent version of this code no longer uses the
    migration code, so this commit moves it to the main RCU source files.

    Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    include/linux/rcupdate.h | 1 -
    include/linux/rcutiny.h | 5 +++
    include/linux/rcutree.h | 1 +
    kernel/rcutree_plugin.h | 71 ++++++++++++++++++++++++++++++++++++++++++++++
    kernel/sched.c | 69 --------------------------------------------
    5 files changed, 77 insertions(+), 70 deletions(-)

    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index 7142ee3..49e8e16 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -66,7 +66,6 @@ extern void call_rcu_sched(struct rcu_head *head,
    extern void synchronize_sched(void);
    extern void rcu_barrier_bh(void);
    extern void rcu_barrier_sched(void);
    -extern void synchronize_sched_expedited(void);
    extern int sched_expedited_torture_stats(char *page);

    static inline void __rcu_read_lock_bh(void)
    diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
    index ea025a6..30ebd7c 100644
    --- a/include/linux/rcutiny.h
    +++ b/include/linux/rcutiny.h
    @@ -60,6 +60,11 @@ static inline void synchronize_rcu_bh_expedited(void)
    synchronize_sched();
    }

    +static inline void synchronize_sched_expedited(void)
    +{
    + synchronize_sched();
    +}
    +
    #ifdef CONFIG_TINY_RCU

    static inline void rcu_preempt_note_context_switch(void)
    diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
    index c0e9683..3a93348 100644
    --- a/include/linux/rcutree.h
    +++ b/include/linux/rcutree.h
    @@ -48,6 +48,7 @@ static inline void exit_rcu(void)
    #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */

    extern void synchronize_rcu_bh(void);
    +extern void synchronize_sched_expedited(void);
    extern void synchronize_rcu_expedited(void);

    static inline void synchronize_rcu_bh_expedited(void)
    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index 71a4147..21df7f3 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -25,6 +25,7 @@
    */

    #include <linux/delay.h>
    +#include <linux/stop_machine.h>

    /*
    * Check the RCU kernel configuration parameters and print informative
    @@ -1014,6 +1015,76 @@ static void __init __rcu_init_preempt(void)

    #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */

    +#ifndef CONFIG_SMP
    +
    +void synchronize_sched_expedited(void)
    +{
    + cond_resched();
    +}
    +EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
    +
    +#else /* #ifndef CONFIG_SMP */
    +
    +static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0);
    +
    +static int synchronize_sched_expedited_cpu_stop(void *data)
    +{
    + /*
    + * There must be a full memory barrier on each affected CPU
    + * between the time that try_stop_cpus() is called and the
    + * time that it returns.
    + *
    + * In the current initial implementation of cpu_stop, the
    + * above condition is already met when the control reaches
    + * this point and the following smp_mb() is not strictly
    + * necessary. Do smp_mb() anyway for documentation and
    + * robustness against future implementation changes.
    + */
    + smp_mb(); /* See above comment block. */
    + return 0;
    +}
    +
    +/*
    + * Wait for an rcu-sched grace period to elapse, but use "big hammer"
    + * approach to force grace period to end quickly. This consumes
    + * significant time on all CPUs, and is thus not recommended for
    + * any sort of common-case code.
    + *
    + * Note that it is illegal to call this function while holding any
    + * lock that is acquired by a CPU-hotplug notifier. Failing to
    + * observe this restriction will result in deadlock.
    + */
    +void synchronize_sched_expedited(void)
    +{
    + int snap, trycount = 0;
    +
    + smp_mb(); /* ensure prior mod happens before capturing snap. */
    + snap = atomic_read(&synchronize_sched_expedited_count) + 1;
    + get_online_cpus();
    + while (try_stop_cpus(cpu_online_mask,
    + synchronize_sched_expedited_cpu_stop,
    + NULL) == -EAGAIN) {
    + put_online_cpus();
    + if (trycount++ < 10)
    + udelay(trycount * num_online_cpus());
    + else {
    + synchronize_sched();
    + return;
    + }
    + if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {
    + smp_mb(); /* ensure test happens before caller kfree */
    + return;
    + }
    + get_online_cpus();
    + }
    + atomic_inc(&synchronize_sched_expedited_count);
    + smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */
    + put_online_cpus();
    +}
    +EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
    +
    +#endif /* #else #ifndef CONFIG_SMP */
    +
    #if !defined(CONFIG_RCU_FAST_NO_HZ)

    /*
    diff --git a/kernel/sched.c b/kernel/sched.c
    index ae8f75a..d1e8889 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -9131,72 +9131,3 @@ struct cgroup_subsys cpuacct_subsys = {
    };
    #endif /* CONFIG_CGROUP_CPUACCT */

    -#ifndef CONFIG_SMP
    -
    -void synchronize_sched_expedited(void)
    -{
    - barrier();
    -}
    -EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
    -
    -#else /* #ifndef CONFIG_SMP */
    -
    -static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0);
    -
    -static int synchronize_sched_expedited_cpu_stop(void *data)
    -{
    - /*
    - * There must be a full memory barrier on each affected CPU
    - * between the time that try_stop_cpus() is called and the
    - * time that it returns.
    - *
    - * In the current initial implementation of cpu_stop, the
    - * above condition is already met when the control reaches
    - * this point and the following smp_mb() is not strictly
    - * necessary. Do smp_mb() anyway for documentation and
    - * robustness against future implementation changes.
    - */
    - smp_mb(); /* See above comment block. */
    - return 0;
    -}
    -
    -/*
    - * Wait for an rcu-sched grace period to elapse, but use "big hammer"
    - * approach to force grace period to end quickly. This consumes
    - * significant time on all CPUs, and is thus not recommended for
    - * any sort of common-case code.
    - *
    - * Note that it is illegal to call this function while holding any
    - * lock that is acquired by a CPU-hotplug notifier. Failing to
    - * observe this restriction will result in deadlock.
    - */
    -void synchronize_sched_expedited(void)
    -{
    - int snap, trycount = 0;
    -
    - smp_mb(); /* ensure prior mod happens before capturing snap. */
    - snap = atomic_read(&synchronize_sched_expedited_count) + 1;
    - get_online_cpus();
    - while (try_stop_cpus(cpu_online_mask,
    - synchronize_sched_expedited_cpu_stop,
    - NULL) == -EAGAIN) {
    - put_online_cpus();
    - if (trycount++ < 10)
    - udelay(trycount * num_online_cpus());
    - else {
    - synchronize_sched();
    - return;
    - }
    - if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) {
    - smp_mb(); /* ensure test happens before caller kfree */
    - return;
    - }
    - get_online_cpus();
    - }
    - atomic_inc(&synchronize_sched_expedited_count);
    - smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */
    - put_online_cpus();
    -}
    -EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
    -
    -#endif /* #else #ifndef CONFIG_SMP */
    --
    1.7.3.2


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