rcu,cleanup: simplify the code when cpu is dying

When we handle the CPU_DYING notifier, the whole system is stopped except
for the current CPU.  We therefore need no synchronization with the other
CPUs.  This allows us to move any orphaned RCU callbacks directly to the
list of any online CPU without needing to run them through the global
orphan lists.  These global orphan lists can therefore be dispensed with.
This commit makes thes changes, though currently victimizes CPU 0 @@@.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 4 insertions, 12 deletions

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);