X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu.c;h=bf2a66bfe3ec360613497d6a7b7c0da2cddc10e9;hb=refs%2Fheads%2Fstable-0.8;hp=a26d38fbaca8286ffe1f6fe3bd522e5a2740a34f;hpb=52c67a3d6139a6bf56b97ed350c7f3beaef3ce67;p=userspace-rcu.git

diff --git a/urcu.c b/urcu.c
index a26d38f..bf2a66b 100644
--- a/urcu.c
+++ b/urcu.c
@@ -64,18 +64,10 @@
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
 /*
- * RCU_MEMBARRIER is only possibly available on Linux.
+ * The ABI of sys_membarrier changed after its original implementation.
+ * Disable it for now. Use RCU_MB flavor instead.
  */
-#if defined(RCU_MEMBARRIER) && defined(__linux__)
-#include <syscall.h>
-#endif
-
-/* If the headers do not support SYS_membarrier, fall back on RCU_MB */
-#ifdef SYS_membarrier
-# define membarrier(...)		syscall(SYS_membarrier, __VA_ARGS__)
-#else
-# define membarrier(...)		-ENOSYS
-#endif
+#define membarrier(...)		-ENOSYS
 
 #define MEMBARRIER_EXPEDITED		(1 << 0)
 #define MEMBARRIER_DELAYED		(1 << 1)
@@ -231,19 +223,27 @@ static void smp_mb_master(int group)
 
 /*
  * synchronize_rcu() waiting. Single thread.
+ * Always called with rcu_registry lock held. Releases this lock and
+ * grabs it again. Holds the lock when it returns.
  */
 static void wait_gp(void)
 {
-	/* Read reader_gp before read futex */
+	/*
+	 * Read reader_gp before read futex. smp_mb_master() needs to
+	 * be called with the rcu registry lock held in RCU_SIGNAL
+	 * flavor.
+	 */
 	smp_mb_master(RCU_MB_GROUP);
+	/* Temporarily unlock the registry lock. */
+	mutex_unlock(&rcu_registry_lock);
 	if (uatomic_read(&rcu_gp.futex) != -1)
-		return;
+		goto end;
 	while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
 			NULL, NULL, 0)) {
 		switch (errno) {
 		case EWOULDBLOCK:
 			/* Value already changed. */
-			return;
+			goto end;
 		case EINTR:
 			/* Retry if interrupted by signal. */
 			break;	/* Get out of switch. */
@@ -252,6 +252,11 @@ static void wait_gp(void)
 			urcu_die(errno);
 		}
 	}
+end:
+	/*
+	 * Re-lock the registry lock before the next loop.
+	 */
+	mutex_lock(&rcu_registry_lock);
 }
 
 /*
@@ -314,14 +319,19 @@ static void wait_for_readers(struct cds_list_head *input_readers,
 			}
 			break;
 		} else {
-			/* Temporarily unlock the registry lock. */
-			mutex_unlock(&rcu_registry_lock);
-			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
+			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+				/* wait_gp unlocks/locks registry lock. */
 				wait_gp();
-			else
+			} else {
+				/* Temporarily unlock the registry lock. */
+				mutex_unlock(&rcu_registry_lock);
 				caa_cpu_relax();
-			/* Re-lock the registry lock before the next loop. */
-			mutex_lock(&rcu_registry_lock);
+				/*
+				 * Re-lock the registry lock before the
+				 * next loop.
+				 */
+				mutex_lock(&rcu_registry_lock);
+			}
 		}
 #else /* #ifndef HAS_INCOHERENT_CACHES */
 		/*
@@ -341,16 +351,20 @@ static void wait_for_readers(struct cds_list_head *input_readers,
 				smp_mb_master(RCU_MB_GROUP);
 				wait_gp_loops = 0;
 			}
-			/* Temporarily unlock the registry lock. */
-			mutex_unlock(&rcu_registry_lock);
 			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+				/* wait_gp unlocks/locks registry lock. */
 				wait_gp();
 				wait_gp_loops++;
 			} else {
+				/* Temporarily unlock the registry lock. */
+				mutex_unlock(&rcu_registry_lock);
 				caa_cpu_relax();
+				/*
+				 * Re-lock the registry lock before the
+				 * next loop.
+				 */
+				mutex_lock(&rcu_registry_lock);
 			}
-			/* Re-lock the registry lock before the next loop. */
-			mutex_lock(&rcu_registry_lock);
 		}
 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 	}