[PATCH] files: rcuref APIs

Adds a set of primitives to do reference counting for objects that are looked
up without locks using RCU.

Signed-off-by: Ravikiran Thirumalai <kiran_th@gmail.com>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f436993bd590..bef3b6901b76 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -45,6 +45,7 @@
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/rcupdate.h>
+#include <linux/rcuref.h>
 #include <linux/cpu.h>
 
 /* Definition for rcupdate control block. */
@@ -72,6 +73,19 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
 static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
 static int maxbatch = 10;
 
+#ifndef __HAVE_ARCH_CMPXCHG
+/*
+ * We use an array of spinlocks for the rcurefs -- similar to ones in sparc
+ * 32 bit atomic_t implementations, and a hash function similar to that
+ * for our refcounting needs.
+ * Can't help multiprocessors which donot have cmpxchg :(
+ */
+
+spinlock_t __rcuref_hash[RCUREF_HASH_SIZE] = {
+        [0 ... (RCUREF_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED
+};
+#endif
+
 /**
  * call_rcu - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.