1 files changed, 61 insertions, 24 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 5ca2d26c5971..0bdb592eee66 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -160,11 +160,51 @@ static int rcu_preempted_readers(struct rcu_node *rnp)
         return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
 }
 
+/*
+ * Record a quiescent state for all tasks that were previously queued
+ * on the specified rcu_node structure and that were blocking the current
+ * RCU grace period.  The caller must hold the specified rnp->lock with
+ * irqs disabled, and this lock is released upon return, but irqs remain
+ * disabled.
+ */
+static void task_quiet(struct rcu_node *rnp, unsigned long flags)
+        __releases(rnp->lock)
+{
+        unsigned long mask;
+        struct rcu_node *rnp_p;
+
+        if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
+                spin_unlock_irqrestore(&rnp->lock, flags);
+                return;  /* Still need more quiescent states! */
+        }
+
+        rnp_p = rnp->parent;
+        if (rnp_p == NULL) {
+                /*
+                 * Either there is only one rcu_node in the tree,
+                 * or tasks were kicked up to root rcu_node due to
+                 * CPUs going offline.
+                 */
+                cpu_quiet_msk_finish(&rcu_preempt_state, flags);
+                return;
+        }
+
+        /* Report up the rest of the hierarchy. */
+        mask = rnp->grpmask;
+        spin_unlock(&rnp->lock);        /* irqs remain disabled. */
+        spin_lock(&rnp_p->lock);        /* irqs already disabled. */
+        cpu_quiet_msk(mask, &rcu_preempt_state, rnp_p, flags);
+}
+
+/*
+ * Handle special cases during rcu_read_unlock(), such as needing to
+ * notify RCU core processing or task having blocked during the RCU
+ * read-side critical section.
+ */
 static void rcu_read_unlock_special(struct task_struct *t)
 {
         int empty;
         unsigned long flags;
-        unsigned long mask;
         struct rcu_node *rnp;
         int special;
 
@@ -213,30 +253,15 @@ static void rcu_read_unlock_special(struct task_struct *t)
                 /*
                  * If this was the last task on the current list, and if
                  * we aren't waiting on any CPUs, report the quiescent state.
-                 * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk()
-                 * drop rnp->lock and restore irq.
+                 * Note that task_quiet() releases rnp->lock.
                  */
-                if (!empty && rnp->qsmask == 0 &&
-                    !rcu_preempted_readers(rnp)) {
-                        struct rcu_node *rnp_p;
-
-                        if (rnp->parent == NULL) {
-                                /* Only one rcu_node in the tree. */
-                                cpu_quiet_msk_finish(&rcu_preempt_state, flags);
-                                return;
-                        }
-                        /* Report up the rest of the hierarchy. */
-                        mask = rnp->grpmask;
+                if (empty)
                         spin_unlock_irqrestore(&rnp->lock, flags);
-                        rnp_p = rnp->parent;
-                        spin_lock_irqsave(&rnp_p->lock, flags);
-                        WARN_ON_ONCE(rnp->qsmask);
-                        cpu_quiet_msk(mask, &rcu_preempt_state, rnp_p, flags);
-                        return;
-                }
-                spin_unlock(&rnp->lock);
+                else
+                        task_quiet(rnp, flags);
+        } else {
+                local_irq_restore(flags);
         }
-        local_irq_restore(flags);
 }
 
 /*
@@ -303,6 +328,8 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
  * rcu_node.  The reason for not just moving them to the immediate
  * parent is to remove the need for rcu_read_unlock_special() to
  * make more than two attempts to acquire the target rcu_node's lock.
+ * Returns true if there were tasks blocking the current RCU grace
+ * period.
  *
  * Returns 1 if there was previously a task blocking the current grace
  * period on the specified rcu_node structure.
@@ -316,7 +343,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
         int i;
         struct list_head *lp;
         struct list_head *lp_root;
-        int retval = rcu_preempted_readers(rnp);
+        int retval;
         struct rcu_node *rnp_root = rcu_get_root(rsp);
         struct task_struct *tp;
 
@@ -334,6 +361,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
          * rcu_nodes in terms of gp_num value.  This fact allows us to
          * move the blocked_tasks[] array directly, element by element.
          */
+        retval = rcu_preempted_readers(rnp);
         for (i = 0; i < 2; i++) {
                 lp = &rnp->blocked_tasks[i];
                 lp_root = &rnp_root->blocked_tasks[i];
@@ -346,7 +374,6 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
                         spin_unlock(&rnp_root->lock); /* irqs remain disabled */
                 }
         }
-
         return retval;
 }
 
@@ -512,6 +539,16 @@ static int rcu_preempted_readers(struct rcu_node *rnp)
         return 0;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/* Because preemptible RCU does not exist, no quieting of tasks. */
+static void task_quiet(struct rcu_node *rnp, unsigned long flags)
+{
+        spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
 
 /*