4 files changed, 31 insertions, 78 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ccdc04c47981..669d7fe049d1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -67,9 +67,6 @@ static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
         .gpnum = -300, \
         .completed = -300, \
         .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname.onofflock), \
-        .orphan_cbs_list = NULL, \
-        .orphan_cbs_tail = &structname.orphan_cbs_list, \
-        .orphan_qlen = 0, \
         .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \
         .n_force_qs = 0, \
         .n_force_qs_ngp = 0, \
@@ -984,53 +981,31 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
 #ifdef CONFIG_HOTPLUG_CPU
 
 /*
- * Move a dying CPU's RCU callbacks to the ->orphan_cbs_list for the
- * specified flavor of RCU.  The callbacks will be adopted by the next
- * _rcu_barrier() invocation or by the CPU_DEAD notifier, whichever
- * comes first.  Because this is invoked from the CPU_DYING notifier,
- * irqs are already disabled.
+ * Move a dying CPU's RCU callbacks to online CPU's callback list.
+ * Synchronization is not required because this function executes
+ * in stop_machine() context.
  */
-static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
+static void rcu_send_cbs_to_online(struct rcu_state *rsp)
 {
         int i;
+        /* current DYING CPU is cleared in the cpu_online_mask */
+        int receive_cpu = cpumask_any(cpu_online_mask);
         struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
+        struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
 
         if (rdp->nxtlist == NULL)
                 return;  /* irqs disabled, so comparison is stable. */
-        raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
-        *rsp->orphan_cbs_tail = rdp->nxtlist;
-        rsp->orphan_cbs_tail = rdp->nxttail[RCU_NEXT_TAIL];
+
+        *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
+        receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+        receive_rdp->qlen += rdp->qlen;
+        receive_rdp->n_cbs_adopted += rdp->qlen;
+        rdp->n_cbs_orphaned += rdp->qlen;
+
         rdp->nxtlist = NULL;
         for (i = 0; i < RCU_NEXT_SIZE; i++)
                 rdp->nxttail[i] = &rdp->nxtlist;
-        rsp->orphan_qlen += rdp->qlen;
-        rdp->n_cbs_orphaned += rdp->qlen;
         rdp->qlen = 0;
-        raw_spin_unlock(&rsp->onofflock);  /* irqs remain disabled. */
-}
-
-/*
- * Adopt previously orphaned RCU callbacks.
- */
-static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
-{
-        unsigned long flags;
-        struct rcu_data *rdp;
-
-        raw_spin_lock_irqsave(&rsp->onofflock, flags);
-        rdp = this_cpu_ptr(rsp->rda);
-        if (rsp->orphan_cbs_list == NULL) {
-                raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
-                return;
-        }
-        *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_list;
-        rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_tail;
-        rdp->qlen += rsp->orphan_qlen;
-        rdp->n_cbs_adopted += rsp->orphan_qlen;
-        rsp->orphan_cbs_list = NULL;
-        rsp->orphan_cbs_tail = &rsp->orphan_cbs_list;
-        rsp->orphan_qlen = 0;
-        raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
 }
 
 /*
@@ -1081,8 +1056,6 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
         if (need_report & RCU_OFL_TASKS_EXP_GP)
                 rcu_report_exp_rnp(rsp, rnp);
-
-        rcu_adopt_orphan_cbs(rsp);
 }
 
 /*
@@ -1100,11 +1073,7 @@ static void rcu_offline_cpu(int cpu)
 
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
 
-static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
-{
-}
-
-static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
+static void rcu_send_cbs_to_online(struct rcu_state *rsp)
 {
 }
 
@@ -1702,10 +1671,7 @@ static void _rcu_barrier(struct rcu_state *rsp,
          * early.
          */
         atomic_set(&rcu_barrier_cpu_count, 1);
-        preempt_disable(); /* stop CPU_DYING from filling orphan_cbs_list */
-        rcu_adopt_orphan_cbs(rsp);
         on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
-        preempt_enable(); /* CPU_DYING can again fill orphan_cbs_list */
         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
                 complete(&rcu_barrier_completion);
         wait_for_completion(&rcu_barrier_completion);
@@ -1831,18 +1797,13 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
         case CPU_DYING:
         case CPU_DYING_FROZEN:
                 /*
-                 * preempt_disable() in _rcu_barrier() prevents stop_machine(),
-                 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
-                 * returns, all online cpus have queued rcu_barrier_func().
-                 * The dying CPU clears its cpu_online_mask bit and
-                 * moves all of its RCU callbacks to ->orphan_cbs_list
-                 * in the context of stop_machine(), so subsequent calls
-                 * to _rcu_barrier() will adopt these callbacks and only
-                 * then queue rcu_barrier_func() on all remaining CPUs.
+                 * The whole machine is "stopped" except this cpu, so we can
+                 * touch any data without introducing corruption. And we send
+                 * the callbacks to an attribute chosen online cpu.
                  */
-                rcu_send_cbs_to_orphanage(&rcu_bh_state);
-                rcu_send_cbs_to_orphanage(&rcu_sched_state);
-                rcu_preempt_send_cbs_to_orphanage();
+                rcu_send_cbs_to_online(&rcu_bh_state);
+                rcu_send_cbs_to_online(&rcu_sched_state);
+                rcu_preempt_send_cbs_to_online();
                 break;
         case CPU_DEAD:
         case CPU_DEAD_FROZEN:
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 91d4170c5c13..1a54be2a902f 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -203,8 +203,8 @@ struct rcu_data {
         long            qlen_last_fqs_check;
                                         /* qlen at last check for QS forcing */
         unsigned long   n_cbs_invoked;  /* count of RCU cbs invoked. */
-        unsigned long   n_cbs_orphaned; /* RCU cbs sent to orphanage. */
-        unsigned long   n_cbs_adopted;  /* RCU cbs adopted from orphanage. */
+        unsigned long   n_cbs_orphaned; /* RCU cbs orphaned by dying CPU */
+        unsigned long   n_cbs_adopted;  /* RCU cbs adopted from dying CPU */
         unsigned long   n_force_qs_snap;
                                         /* did other CPU force QS recently? */
         long            blimit;         /* Upper limit on a processed batch */
@@ -309,15 +309,7 @@ struct rcu_state {
         /* End of fields guarded by root rcu_node's lock. */
 
         raw_spinlock_t onofflock;               /* exclude on/offline and */
-                                                /*  starting new GP.  Also */
-                                                /*  protects the following */
-                                                /*  orphan_cbs fields. */
-        struct rcu_head *orphan_cbs_list;       /* list of rcu_head structs */
-                                                /*  orphaned by all CPUs in */
-                                                /*  a given leaf rcu_node */
-                                                /*  going offline. */
-        struct rcu_head **orphan_cbs_tail;      /* And tail pointer. */
-        long orphan_qlen;                       /* Number of orphaned cbs. */
+                                                /*  starting new GP. */
         raw_spinlock_t fqslock;                 /* Only one task forcing */
                                                 /*  quiescent states. */
         unsigned long jiffies_force_qs;         /* Time at which to invoke */
@@ -390,7 +382,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
 static int rcu_preempt_pending(int cpu);
 static int rcu_preempt_needs_cpu(int cpu);
 static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
-static void rcu_preempt_send_cbs_to_orphanage(void);
+static void rcu_preempt_send_cbs_to_online(void);
 static void __init __rcu_init_preempt(void);
 static void rcu_needs_cpu_flush(void);
 
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 21df7f3e7273..0de359be5b41 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -774,11 +774,11 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 }
 
 /*
- * Move preemptable RCU's callbacks to ->orphan_cbs_list.
+ * Move preemptable DYING RCU's callbacks to other online CPU.
  */
-static void rcu_preempt_send_cbs_to_orphanage(void)
+static void rcu_preempt_send_cbs_to_online(void)
 {
-        rcu_send_cbs_to_orphanage(&rcu_preempt_state);
+        rcu_send_cbs_to_online(&rcu_preempt_state);
 }
 
 /*
@@ -1002,7 +1002,7 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 /*
  * Because there is no preemptable RCU, there are no callbacks to move.
  */
-static void rcu_preempt_send_cbs_to_orphanage(void)
+static void rcu_preempt_send_cbs_to_online(void)
 {
 }
 
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 78ad3c35b683..c8e97853b970 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -166,13 +166,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 
         gpnum = rsp->gpnum;
         seq_printf(m, "c=%lu g=%lu s=%d jfq=%ld j=%x "
-                      "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld\n",
+                      "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu\n",
                    rsp->completed, gpnum, rsp->signaled,
                    (long)(rsp->jiffies_force_qs - jiffies),
                    (int)(jiffies & 0xffff),
                    rsp->n_force_qs, rsp->n_force_qs_ngp,
                    rsp->n_force_qs - rsp->n_force_qs_ngp,
-                   rsp->n_force_qs_lh, rsp->orphan_qlen);
+                   rsp->n_force_qs_lh);
         for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < NUM_RCU_NODES; rnp++) {
                 if (rnp->level != level) {
                         seq_puts(m, "\n");