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    Subject[PATCH RFC tip/core/rcu 07/18] rcu: eliminate rcu_process_dyntick() return value
    Date
    From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    Proposed for 2.6.34, not for inclusion.

    Because a new grace period cannot start while we are executing within the
    force_quiescent_state() function's switch statement, if any test within
    that switch statement or within any function called from that switch
    statement shows that the current grace period has ended, we can safely
    re-do that test any time before we leave the switch statement. This
    means that we no longer need a return value from rcu_process_dyntick(),
    as we can simply invoke rcu_gp_in_progress() to check whether the old
    grace period has finished -- there is no longer any need to worry about
    whether or not a new grace period has been started.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcutree.c | 17 ++++++-----------
    1 files changed, 6 insertions(+), 11 deletions(-)

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index c7d0070..e497119 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -1144,11 +1144,9 @@ void rcu_check_callbacks(int cpu, int user)
    /*
    * Scan the leaf rcu_node structures, processing dyntick state for any that
    * have not yet encountered a quiescent state, using the function specified.
    - * Returns 1 if the current grace period ends while scanning (possibly
    - * because we made it end).
    */
    -static int rcu_process_dyntick(struct rcu_state *rsp,
    - int (*f)(struct rcu_data *))
    +static void rcu_process_dyntick(struct rcu_state *rsp,
    + int (*f)(struct rcu_data *))
    {
    unsigned long bit;
    int cpu;
    @@ -1161,7 +1159,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp,
    spin_lock_irqsave(&rnp->lock, flags);
    if (rnp->completed != rsp->gpnum - 1) {
    spin_unlock_irqrestore(&rnp->lock, flags);
    - return 1;
    + return;
    }
    if (rnp->qsmask == 0) {
    spin_unlock_irqrestore(&rnp->lock, flags);
    @@ -1181,7 +1179,6 @@ static int rcu_process_dyntick(struct rcu_state *rsp,
    }
    spin_unlock_irqrestore(&rnp->lock, flags);
    }
    - return 0;
    }

    /*
    @@ -1193,7 +1190,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
    unsigned long flags;
    struct rcu_node *rnp = rcu_get_root(rsp);
    u8 forcenow;
    - u8 gpdone;

    if (!rcu_gp_in_progress(rsp))
    return; /* No grace period in progress, nothing to force. */
    @@ -1226,10 +1222,9 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
    break; /* So gcc recognizes the dead code. */

    /* Record dyntick-idle state. */
    - gpdone = rcu_process_dyntick(rsp,
    - dyntick_save_progress_counter);
    + rcu_process_dyntick(rsp, dyntick_save_progress_counter);
    spin_lock(&rnp->lock); /* irqs already disabled */
    - if (gpdone)
    + if (!rcu_gp_in_progress(rsp))
    break;
    /* fall into next case. */

    @@ -1249,7 +1244,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)

    /* Check dyntick-idle state, send IPI to laggarts. */
    spin_unlock(&rnp->lock); /* irqs remain disabled */
    - gpdone = rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);
    + rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);

    /* Leave state in case more forcing is required. */

    --
    1.5.2.5


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