rcu: Make hot-unplugged CPU relinquish its own RCU callbacks

The current interaction between RCU and CPU hotplug requires that
RCU block in CPU notifiers waiting for callbacks to drain.

This can be greatly simplified by having each CPU relinquish its
own callbacks, and for both _rcu_barrier() and CPU_DEAD notifiers
to adopt all callbacks that were previously relinquished.

This change also eliminates the possibility of certain types of
hangs due to the previous practice of waiting for callbacks to be
invoked from within CPU notifiers.  If you don't every wait, you
cannot hang.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
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: <1254890898456-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 1 deletions

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 676eecd371d9..b40ac5706040 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -244,7 +244,15 @@ struct rcu_state {
         /* End  of fields guarded by root rcu_node's lock. */
 
         spinlock_t onofflock;                   /* exclude on/offline and */
-                                                /*  starting new GP. */
+                                                /*  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. */
         spinlock_t fqslock;                     /* Only one task forcing */
                                                 /*  quiescent states. */
         unsigned long jiffies_force_qs;         /* Time at which to invoke */
@@ -305,6 +313,7 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
 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 __init __rcu_init_preempt(void);
 
 #endif /* #else #ifdef RCU_TREE_NONCORE */