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    Subject[tip:core/rcu] rcu: Further cleanups of use of lastcomp
    Commit-ID:  560d4bc0df9a5e63b980432282d8c2bd3559ec74
    Gitweb: http://git.kernel.org/tip/560d4bc0df9a5e63b980432282d8c2bd3559ec74
    Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    AuthorDate: Fri, 13 Nov 2009 19:51:38 -0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Sat, 14 Nov 2009 10:31:42 +0100

    rcu: Further cleanups of use of lastcomp

    Now that a copy of the rsp->completed flag is available in all
    rcu_node structures, make full use of it. It is still
    legitimate to access rsp->completed while holding the root
    rcu_node structure's lock, however.

    Also, tighten up force_quiescent_state()'s checks for end of
    current grace period.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: laijs@cn.fujitsu.com
    Cc: dipankar@in.ibm.com
    Cc: mathieu.desnoyers@polymtl.ca
    Cc: josh@joshtriplett.org
    Cc: dvhltc@us.ibm.com
    Cc: niv@us.ibm.com
    Cc: peterz@infradead.org
    Cc: rostedt@goodmis.org
    Cc: Valdis.Kletnieks@vt.edu
    Cc: dhowells@redhat.com
    LKML-Reference: <1258170699933-git-send-email->
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/rcutree.c | 13 ++++++-------
    1 files changed, 6 insertions(+), 7 deletions(-)

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index 3df0438..24bbf2c 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -817,7 +817,7 @@ cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)

    rnp = rdp->mynode;
    spin_lock_irqsave(&rnp->lock, flags);
    - if (lastcomp != ACCESS_ONCE(rsp->completed)) {
    + if (lastcomp != rnp->completed) {

    /*
    * Someone beat us to it for this grace period, so leave.
    @@ -935,7 +935,6 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
    static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
    {
    unsigned long flags;
    - long lastcomp;
    unsigned long mask;
    struct rcu_data *rdp = rsp->rda[cpu];
    struct rcu_node *rnp;
    @@ -971,7 +970,6 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
    spin_unlock(&rnp->lock); /* irqs remain disabled. */
    rnp = rnp->parent;
    } while (rnp != NULL);
    - lastcomp = rsp->completed;

    spin_unlock_irqrestore(&rsp->onofflock, flags);

    @@ -1145,7 +1143,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
    rcu_for_each_leaf_node(rsp, rnp) {
    mask = 0;
    spin_lock_irqsave(&rnp->lock, flags);
    - if (rsp->completed != lastcomp) {
    + if (rnp->completed != lastcomp) {
    spin_unlock_irqrestore(&rnp->lock, flags);
    return 1;
    }
    @@ -1159,7 +1157,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
    if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
    mask |= bit;
    }
    - if (mask != 0 && rsp->completed == lastcomp) {
    + if (mask != 0 && rnp->completed == lastcomp) {

    /* cpu_quiet_msk() releases rnp->lock. */
    cpu_quiet_msk(mask, rsp, rnp, flags);
    @@ -1196,7 +1194,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
    lastcomp = rsp->gpnum - 1;
    signaled = rsp->signaled;
    rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
    - if (lastcomp == rsp->gpnum) {
    + if(!rcu_gp_in_progress(rsp)) {
    rsp->n_force_qs_ngp++;
    spin_unlock(&rnp->lock);
    goto unlock_ret; /* no GP in progress, time updated. */
    @@ -1224,7 +1222,8 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
    /* Update state, record completion counter. */
    forcenow = 0;
    spin_lock(&rnp->lock);
    - if (lastcomp == rsp->completed &&
    + if (lastcomp + 1 == rsp->gpnum &&
    + lastcomp == rsp->completed &&
    rsp->signaled == signaled) {
    rsp->signaled = RCU_FORCE_QS;
    rsp->completed_fqs = lastcomp;

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