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    Subject[PATCH tip/core/rcu 01/18] rcu: Use rsp->expedited_wq instead of sync_rcu_preempt_exp_wq
    Date
    Now that there is an ->expedited_wq waitqueue in each rcu_state structure,
    there is no need for the sync_rcu_preempt_exp_wq global variable. This
    commit therefore substitutes ->expedited_wq for sync_rcu_preempt_exp_wq.
    It also initializes ->expedited_wq only once at boot instead of at the
    start of each expedited grace period.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcu/tree.c | 2 +-
    kernel/rcu/tree_plugin.h | 6 ++----
    2 files changed, 3 insertions(+), 5 deletions(-)

    diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    index 775d36cc0050..53d66ebb4811 100644
    --- a/kernel/rcu/tree.c
    +++ b/kernel/rcu/tree.c
    @@ -3556,7 +3556,6 @@ void synchronize_sched_expedited(void)
    rcu_exp_gp_seq_start(rsp);

    /* Stop each CPU that is online, non-idle, and not us. */
    - init_waitqueue_head(&rsp->expedited_wq);
    atomic_set(&rsp->expedited_need_qs, 1); /* Extra count avoids race. */
    for_each_online_cpu(cpu) {
    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
    @@ -4179,6 +4178,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
    }

    init_waitqueue_head(&rsp->gp_wq);
    + init_waitqueue_head(&rsp->expedited_wq);
    rnp = rsp->level[rcu_num_lvls - 1];
    for_each_possible_cpu(i) {
    while (i > rnp->grphi)
    diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
    index b2bf3963a0ae..72df006de798 100644
    --- a/kernel/rcu/tree_plugin.h
    +++ b/kernel/rcu/tree_plugin.h
    @@ -535,8 +535,6 @@ void synchronize_rcu(void)
    }
    EXPORT_SYMBOL_GPL(synchronize_rcu);

    -static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
    -
    /*
    * Return non-zero if there are any tasks in RCU read-side critical
    * sections blocking the current preemptible-RCU expedited grace period.
    @@ -590,7 +588,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
    raw_spin_unlock_irqrestore(&rnp->lock, flags);
    if (wake) {
    smp_mb(); /* EGP done before wake_up(). */
    - wake_up(&sync_rcu_preempt_exp_wq);
    + wake_up(&rsp->expedited_wq);
    }
    break;
    }
    @@ -729,7 +727,7 @@ void synchronize_rcu_expedited(void)

    /* Wait for snapshotted ->blkd_tasks lists to drain. */
    rnp = rcu_get_root(rsp);
    - wait_event(sync_rcu_preempt_exp_wq,
    + wait_event(rsp->expedited_wq,
    sync_rcu_preempt_exp_done(rnp));

    /* Clean up and exit. */
    --
    2.5.2


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