X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.h;h=3e1ad78324cda478711e1c3f521bd62359bd2212;hp=03764ab33dbe241b643b72ef9cbfd6757662fa3b;hb=82faadb56d6001ee1dc0bc5b3f22de49cd0ec2fe;hpb=bb48818526ec4317f9e6daeb0aa1cd64d528f754

diff --git a/urcu.h b/urcu.h
index 03764ab..3e1ad78 100644
--- a/urcu.h
+++ b/urcu.h
@@ -26,10 +26,36 @@
 #define likely(x)       __builtin_expect(!!(x), 1)
 #define unlikely(x)     __builtin_expect(!!(x), 0)
 
+/* Assume P4 or newer */
+#define CONFIG_HAS_FENCE 1
+
 /* x86 32/64 specific */
+#ifdef CONFIG_HAS_FENCE
 #define mb()    asm volatile("mfence":::"memory")
 #define rmb()   asm volatile("lfence":::"memory")
-#define wmb()   asm volatile("sfence" ::: "memory")
+#define wmb()   asm volatile("sfence"::: "memory")
+#else
+/*
+ * Some non-Intel clones support out of order store. wmb() ceases to be a
+ * nop for these.
+ */
+#define mb()    asm volatile("lock; addl $0,0(%%esp)":::"memory")
+#define rmb()   asm volatile("lock; addl $0,0(%%esp)":::"memory")
+#define wmb()   asm volatile("lock; addl $0,0(%%esp)"::: "memory")
+#endif
+
+/* Assume SMP machine, given we don't have this information */
+#define CONFIG_SMP 1
+
+#ifdef CONFIG_SMP
+#define smp_mb()	mb()
+#define smp_rmb()	rmb()
+#define smp_wmb()	wmb()
+#else
+#define smp_mb()	barrier()
+#define smp_rmb()	barrier()
+#define smp_wmb()	barrier()
+#endif
 
 static inline void atomic_inc(int *v)
 {
@@ -117,6 +143,13 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
 
 #define SIGURCU SIGUSR1
 
+/*
+ * If a reader is really non-cooperative and refuses to commit its
+ * urcu_active_readers count to memory (there is no barrier in the reader
+ * per-se), kick it after a few loops waiting for it.
+ */
+#define KICK_READER_LOOPS 10000
+
 #ifdef DEBUG_YIELD
 #include <sched.h>
 #include <time.h>
@@ -173,7 +206,7 @@ static inline void debug_yield_init(void)
 #ifdef DEBUG_FULL_MB
 static inline void read_barrier()
 {
-	mb();
+	smp_mb();
 }
 #else
 static inline void read_barrier()
@@ -206,45 +239,42 @@ static inline int rcu_old_gp_ongoing(long *value)
 
 	if (value == NULL)
 		return 0;
-	debug_yield_write();
+	/*
+	 * Make sure both tests below are done on the same version of *value
+	 * to insure consistency.
+	 */
 	v = ACCESS_ONCE(*value);
-	debug_yield_write();
 	return (v & RCU_GP_CTR_NEST_MASK) &&
-		 ((v ^ ACCESS_ONCE(urcu_gp_ctr)) & RCU_GP_CTR_BIT);
+		 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
 }
 
 static inline void rcu_read_lock(void)
 {
 	long tmp;
 
-	debug_yield_read();
 	tmp = urcu_active_readers;
-	debug_yield_read();
 	/* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
+	/* The data dependency "read urcu_gp_ctr, write urcu_active_readers",
+	 * serializes those two memory operations. */
 	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK)))
-		urcu_active_readers = urcu_gp_ctr;
+		urcu_active_readers = ACCESS_ONCE(urcu_gp_ctr);
 	else
 		urcu_active_readers = tmp + RCU_GP_COUNT;
-	debug_yield_read();
 	/*
 	 * Increment active readers count before accessing the pointer.
 	 * See force_mb_all_threads().
 	 */
 	read_barrier();
-	debug_yield_read();
 }
 
 static inline void rcu_read_unlock(void)
 {
-	debug_yield_read();
 	read_barrier();
-	debug_yield_read();
 	/*
 	 * Finish using rcu before decrementing the pointer.
 	 * See force_mb_all_threads().
 	 */
 	urcu_active_readers -= RCU_GP_COUNT;
-	debug_yield_read();
 }
 
 /**
@@ -285,7 +315,6 @@ extern void synchronize_rcu(void);
 #define urcu_publish_content(p, v) \
 	({ \
 		void *oldptr; \
-		debug_yield_write(); \
 		oldptr = rcu_xchg_pointer(p, v); \
 		synchronize_rcu(); \
 		oldptr; \