X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu%2Fstatic%2Furcu-qsbr.h;h=f3149569b2a2e2573df57936673d82eaadf0e1d7;hb=f864c15d3148f14019e837544213314db0198ccb;hp=5580092f4159123f3d948e85b5384b0e58c7a27c;hpb=a5a9f428a238e790d6c97299bc214b5cca815cd7;p=urcu.git

diff --git a/urcu/static/urcu-qsbr.h b/urcu/static/urcu-qsbr.h
index 5580092..f314956 100644
--- a/urcu/static/urcu-qsbr.h
+++ b/urcu/static/urcu-qsbr.h
@@ -68,43 +68,43 @@ extern "C" {
 #include <pthread.h>
 #include <unistd.h>
 
-#define YIELD_READ 	(1 << 0)
-#define YIELD_WRITE	(1 << 1)
+#define RCU_YIELD_READ 	(1 << 0)
+#define RCU_YIELD_WRITE	(1 << 1)
 
 /* maximum sleep delay, in us */
 #define MAX_SLEEP 50
 
-extern unsigned int yield_active;
-extern DECLARE_URCU_TLS(unsigned int, rand_yield);
+extern unsigned int rcu_yield_active;
+extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
 
-static inline void debug_yield_read(void)
+static inline void rcu_debug_yield_read(void)
 {
-	if (yield_active & YIELD_READ)
-		if (rand_r(&URCU_TLS(rand_yield)) & 0x1)
-			usleep(rand_r(&URCU_TLS(rand_yield)) % MAX_SLEEP);
+	if (rcu_yield_active & RCU_YIELD_READ)
+		if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
+			usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
 }
 
-static inline void debug_yield_write(void)
+static inline void rcu_debug_yield_write(void)
 {
-	if (yield_active & YIELD_WRITE)
-		if (rand_r(&URCU_TLS(rand_yield)) & 0x1)
-			usleep(rand_r(&URCU_TLS(rand_yield)) % MAX_SLEEP);
+	if (rcu_yield_active & RCU_YIELD_WRITE)
+		if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
+			usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
 }
 
-static inline void debug_yield_init(void)
+static inline void rcu_debug_yield_init(void)
 {
-	URCU_TLS(rand_yield) = time(NULL) ^ pthread_self();
+	URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
 }
 #else
-static inline void debug_yield_read(void)
+static inline void rcu_debug_yield_read(void)
 {
 }
 
-static inline void debug_yield_write(void)
+static inline void rcu_debug_yield_write(void)
 {
 }
 
-static inline void debug_yield_init(void)
+static inline void rcu_debug_yield_init(void)
 {
 
 }
@@ -131,7 +131,7 @@ struct rcu_reader {
 
 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
 
-extern int32_t gp_futex;
+extern int32_t rcu_gp_futex;
 
 /*
  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
@@ -141,10 +141,10 @@ static inline void wake_up_gp(void)
 	if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
 		_CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
 		cmm_smp_mb();
-		if (uatomic_read(&gp_futex) != -1)
+		if (uatomic_read(&rcu_gp_futex) != -1)
 			return;
-		uatomic_set(&gp_futex, 0);
-		futex_noasync(&gp_futex, FUTEX_WAKE, 1,
+		uatomic_set(&rcu_gp_futex, 0);
+		futex_noasync(&rcu_gp_futex, FUTEX_WAKE, 1,
 		      NULL, NULL, 0);
 	}
 }
@@ -180,20 +180,43 @@ static inline void _rcu_read_unlock(void)
 {
 }
 
+/*
+ * This is a helper function for _rcu_quiescent_state().
+ * The first cmm_smp_mb() ensures memory accesses in the prior read-side
+ * critical sections are not reordered with store to
+ * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
+ * offline section that would happen to end with this
+ * rcu_quiescent_state() call are not reordered with
+ * store to URCU_TLS(rcu_reader).ctr.
+ */
+static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
+{
+	cmm_smp_mb();
+	_CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
+	cmm_smp_mb();	/* write URCU_TLS(rcu_reader).ctr before read futex */
+	wake_up_gp();
+	cmm_smp_mb();
+}
+
 /*
  * Inform RCU of a quiescent state.
  *
  * This function is less than 10 lines long.  The intent is that this
  * function meets the 10-line criterion for LGPL, allowing this function
  * to be invoked directly from non-LGPL code.
+ *
+ * We skip the memory barriers and gp store if our local ctr already
+ * matches the global rcu_gp_ctr value: this is OK because a prior
+ * _rcu_quiescent_state() or _rcu_thread_online() already updated it
+ * within our thread, so we have no quiescent state to report.
  */
 static inline void _rcu_quiescent_state(void)
 {
-	cmm_smp_mb();
-	_CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp_ctr));
-	cmm_smp_mb();	/* write URCU_TLS(rcu_reader).ctr before read futex */
-	wake_up_gp();
-	cmm_smp_mb();
+	unsigned long gp_ctr;
+
+	if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp_ctr)) == URCU_TLS(rcu_reader).ctr)
+		return;
+	_rcu_quiescent_state_update_and_wakeup(gp_ctr);
 }
 
 /*