From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Tue, 26 May 2009 17:31:36 +0000 (-0400)
Subject: sync_core to smp_mb transition
X-Git-Tag: v0.1~210
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=5dba80f9bed985c23090ec74bb4173b31b28513a;p=userspace-rcu.git

sync_core to smp_mb transition

- move sync_core to smp_mb in urcu.c, update comments.
- cpuid clashes with -fPIC because it clobbers ebx. Use mb() if ___PIC__ is
  defined.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---

diff --git a/arch_atomic_x86.h b/arch_atomic_x86.h
index 8423ae3..f471a39 100644
--- a/arch_atomic_x86.h
+++ b/arch_atomic_x86.h
@@ -30,7 +30,7 @@
  * Derived from AO_compare_and_swap() and AO_test_and_set_full().
  */
 
-static __attribute__((always_inline))
+static inline __attribute__((always_inline))
 unsigned int atomic_exchange_32(volatile unsigned int *addr, unsigned int val)
 {
 	unsigned int result;
@@ -47,7 +47,7 @@ unsigned int atomic_exchange_32(volatile unsigned int *addr, unsigned int val)
 
 #if (BITS_PER_LONG == 64)
 
-static __attribute__((always_inline))
+static inline __attribute__((always_inline))
 unsigned long atomic_exchange_64(volatile unsigned long *addr,
 				 unsigned long val)
 {
@@ -65,7 +65,7 @@ unsigned long atomic_exchange_64(volatile unsigned long *addr,
 
 #endif
 
-static __attribute__((always_inline))
+static inline __attribute__((always_inline))
 unsigned long _atomic_exchange(volatile void *addr, unsigned long val, int len)
 {
 	switch (len) {
diff --git a/arch_x86.h b/arch_x86.h
index e7d945e..8a57325 100644
--- a/arch_x86.h
+++ b/arch_x86.h
@@ -97,10 +97,22 @@ static inline void cpu_relax(void)
 /*
  * Serialize core instruction execution. Also acts as a compiler barrier.
  */
+#ifdef __PIC__
+/*
+ * Cannot use cpuid because it clobbers the ebx register and clashes
+ * with -fPIC :
+ * error: PIC register 'ebx' clobbered in 'asm'
+ */
+static inline void sync_core(void)
+{
+	mb();
+}
+#else
 static inline void sync_core(void)
 {
 	asm volatile("cpuid" : : : "memory", "eax", "ebx", "ecx", "edx");
 }
+#endif
 
 #define rdtscll(val)							  \
 	do {						  		  \
diff --git a/urcu.c b/urcu.c
index 2a225c4..b71e162 100644
--- a/urcu.c
+++ b/urcu.c
@@ -254,12 +254,11 @@ void synchronize_rcu(void)
 	 */
 
 	/*
-	 * Current RCU formal verification model assumes sequential execution of
-	 * the write-side. Add core synchronization instructions. Can be removed
-	 * if the formal model is extended to prove that reordering is still
-	 * correct.
+	 * Adding a smp_mb() which is _not_ formally required, but makes the
+	 * model easier to understand. It does not have a big performance impact
+	 * anyway, given this is the write-side.
 	 */
-	sync_core();	/* Formal model assumes serialized execution */
+	smp_mb();
 
 	/*
 	 * Wait for previous parity to be empty of readers.
@@ -274,7 +273,12 @@ void synchronize_rcu(void)
 	 * Ensured by STORE_SHARED and LOAD_SHARED.
 	 */
 
-	sync_core();	/* Formal model assumes serialized execution */
+	/*
+	 * Adding a smp_mb() which is _not_ formally required, but makes the
+	 * model easier to understand. It does not have a big performance impact
+	 * anyway, given this is the write-side.
+	 */
+	smp_mb();
 
 	switch_next_urcu_qparity();	/* 1 -> 0 */
 
@@ -286,7 +290,12 @@ void synchronize_rcu(void)
 	 * Ensured by STORE_SHARED and LOAD_SHARED.
 	 */
 
-	sync_core();	/* Formal model assumes serialized execution */
+	/*
+	 * Adding a smp_mb() which is _not_ formally required, but makes the
+	 * model easier to understand. It does not have a big performance impact
+	 * anyway, given this is the write-side.
+	 */
+	smp_mb();
 
 	/*
 	 * Wait for previous parity to be empty of readers.