rcu: Simplify quiescent-state detection

[deliverable/linux.git] / kernel / rcutree.c

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index a2eadd04fb29cd7dfd22f2c128fe15c925d7eb42..6194402ec853b6cf4dbd25a85bb704b004b8073a 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -176,8 +176,6 @@ void rcu_sched_qs(int cpu)
 {
        struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
 
-       rdp->passed_quiesce_gpnum = rdp->gpnum;
-       barrier();
        if (rdp->passed_quiesce == 0)
                trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs");
        rdp->passed_quiesce = 1;
@@ -187,8 +185,6 @@ void rcu_bh_qs(int cpu)
 {
        struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
 
-       rdp->passed_quiesce_gpnum = rdp->gpnum;
-       barrier();
        if (rdp->passed_quiesce == 0)
                trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs");
        rdp->passed_quiesce = 1;
@@ -899,12 +895,8 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct
                 */
                rdp->gpnum = rnp->gpnum;
                trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
-               if (rnp->qsmask & rdp->grpmask) {
-                       rdp->qs_pending = 1;
-                       rdp->passed_quiesce = 0;
-               } else {
-                       rdp->qs_pending = 0;
-               }
+               rdp->passed_quiesce = 0;
+               rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
                zero_cpu_stall_ticks(rdp);
        }
 }
@@ -984,10 +976,13 @@ __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
                 * our behalf. Catch up with this state to avoid noting
                 * spurious new grace periods.  If another grace period
                 * has started, then rnp->gpnum will have advanced, so
-                * we will detect this later on.
+                * we will detect this later on.  Of course, any quiescent
+                * states we found for the old GP are now invalid.
                 */
-               if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
+               if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) {
                        rdp->gpnum = rdp->completed;
+                       rdp->passed_quiesce = 0;
+               }
 
                /*
                 * If RCU does not need a quiescent state from this CPU,
@@ -1358,7 +1353,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
  * based on quiescent states detected in an earlier grace period!
  */
 static void
-rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastgp)
+rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
 {
        unsigned long flags;
        unsigned long mask;
@@ -1366,7 +1361,8 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long las
 
        rnp = rdp->mynode;
        raw_spin_lock_irqsave(&rnp->lock, flags);
-       if (lastgp != rnp->gpnum || rnp->completed == rnp->gpnum) {
+       if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
+           rnp->completed == rnp->gpnum) {
 
                /*
                 * The grace period in which this quiescent state was
@@ -1425,7 +1421,7 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
         * Tell RCU we are done (but rcu_report_qs_rdp() will be the
         * judge of that).
         */
-       rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesce_gpnum);
+       rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -2600,7 +2596,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
                        rdp->completed = rnp->completed;
                        rdp->passed_quiesce = 0;
                        rdp->qs_pending = 0;
-                       rdp->passed_quiesce_gpnum = rnp->gpnum - 1;
                        trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");
                }
                raw_spin_unlock(&rnp->lock); /* irqs already disabled. */