X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-bp.c;h=20684cc4d0972a61427f8ecae0e5fd7eb5072189;hp=4dc402865a026800ccef0bb35378be6241c81505;hb=6a00c945d10d68e174c9fe96b2a98eb124b0d77e;hpb=731ccb963c80afd067e20acee2f9bd7cb4875ffb

diff --git a/urcu-bp.c b/urcu-bp.c
index 4dc4028..20684cc 100644
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -36,6 +36,7 @@
 #include <unistd.h>
 #include <sys/mman.h>
 
+#include "urcu/arch.h"
 #include "urcu/wfcqueue.h"
 #include "urcu/map/urcu-bp.h"
 #include "urcu/static/urcu-bp.h"
@@ -94,11 +95,25 @@ void *mremap_wrapper(void *old_address, size_t old_size,
 static
 int rcu_bp_refcount;
 
+/* If the headers do not support membarrier system call, fall back smp_mb. */
+#ifdef __NR_membarrier
+# define membarrier(...)		syscall(__NR_membarrier, __VA_ARGS__)
+#else
+# define membarrier(...)		-ENOSYS
+#endif
+
+enum membarrier_cmd {
+	MEMBARRIER_CMD_QUERY = 0,
+	MEMBARRIER_CMD_SHARED = (1 << 0),
+};
+
 static
 void __attribute__((constructor)) rcu_bp_init(void);
 static
 void __attribute__((destructor)) rcu_bp_exit(void);
 
+int urcu_bp_has_sys_membarrier;
+
 /*
  * rcu_gp_lock ensures mutual exclusion between threads calling
  * synchronize_rcu().
@@ -174,6 +189,14 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 		urcu_die(ret);
 }
 
+static void smp_mb_master(void)
+{
+	if (caa_likely(urcu_bp_has_sys_membarrier))
+		(void) membarrier(MEMBARRIER_CMD_SHARED, 0);
+	else
+		cmm_smp_mb();
+}
+
 /*
  * Always called with rcu_registry lock held. Releases this lock between
  * iterations and grabs it again. Holds the lock when it returns.
@@ -254,7 +277,7 @@ void synchronize_rcu(void)
 	/* All threads should read qparity before accessing data structure
 	 * where new ptr points to. */
 	/* Write new ptr before changing the qparity */
-	cmm_smp_mb();
+	smp_mb_master();
 
 	/*
 	 * Wait for readers to observe original parity or be quiescent.
@@ -303,7 +326,7 @@ void synchronize_rcu(void)
 	 * Finish waiting for reader threads before letting the old ptr being
 	 * freed.
 	 */
-	cmm_smp_mb();
+	smp_mb_master();
 out:
 	mutex_unlock(&rcu_registry_lock);
 	mutex_unlock(&rcu_gp_lock);
@@ -567,6 +590,10 @@ void rcu_bp_init(void)
 				urcu_bp_thread_exit_notifier);
 		if (ret)
 			abort();
+		ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
+		if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
+			urcu_bp_has_sys_membarrier = 1;
+		}
 		initialized = 1;
 	}
 	mutex_unlock(&init_lock);