From e462817ecdce42b00f0cb0825e2425b08943105b Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Mon, 9 Feb 2009 00:29:58 -0500
Subject: [PATCH] Add rcu_assign_pointer

rcu_assign_pointer has a memory barrier which lets the writer make sure the data
has been properly written to memory before setting the pointer.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
 Makefile |  4 ++++
 urcu.c   |  2 +-
 urcu.h   | 22 ++++++++++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 8c343cc..8224567 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,10 @@ urcu-asm.S: urcu-asm.c urcu.h
 urcu-asm.o: urcu-asm.c urcu.h
 	$(CC) ${CFLAGS} -c -o $@ $(SRC_DEP)
 
+#in progress...
+urcutorture.o: urcutorture.c urcu.o urcu.h rcutorture.h
+	$(CC) ${CFLAGS} $(LDFLAGS) -o $@ $(SRC_DEP)
+
 .PHONY: clean
 
 clean:
diff --git a/urcu.c b/urcu.c
index 31cdf6f..23a985b 100644
--- a/urcu.c
+++ b/urcu.c
@@ -174,7 +174,7 @@ void *urcu_publish_content(void **ptr, void *new)
 	 */
 	oldptr = *ptr;
 	debug_yield_write();
-	*ptr = new;
+	rcu_assign_pointer(*ptr, new);
 
 	debug_yield_write();
 	switch_qparity();
diff --git a/urcu.h b/urcu.h
index 01a4c68..27695d4 100644
--- a/urcu.h
+++ b/urcu.h
@@ -169,7 +169,29 @@ static inline void rcu_read_unlock(void)
 	debug_yield_read();
 }
 
+/**
+ * rcu_assign_pointer - assign (publicize) a pointer to a newly
+ * initialized structure that will be dereferenced by RCU read-side
+ * critical sections.  Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the pointer assignment.  More importantly, this
+ * call documents which pointers will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_pointer(p, v) \
+	({ \
+		if (!__builtin_constant_p(v) || \
+		    ((v) != NULL)) \
+			wmb(); \
+		(p) = (v); \
+	})
+
 extern void *urcu_publish_content(void **ptr, void *new);
+extern void synchronize_rcu(void);
 
 /*
  * Reader thread registration.
-- 
2.34.1