X-Git-Url: http://git.efficios.com/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fmain.c;h=3d2cad9361464534128a44f5917d01f1e58899fe;hp=0625c11939b958f8b9d88ed3ce48a88a3074d703;hb=8b0d46366f5c87043d22aa29b9f26e5249bf7c3a;hpb=9cc1ba3b1f895beb3ef4b10009372f6a859068dd

diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index 0625c1193..3d2cad936 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -332,7 +332,8 @@ struct lttng_ht *agent_apps_ht_by_sock = NULL;
  *  - rotation_thread
  *  - health_thread
  */
-int lttng_sessiond_ready = 4;
+#define NR_LTTNG_SESSIOND_SUPPORT_THREADS 4
+int lttng_sessiond_ready = NR_LTTNG_SESSIOND_SUPPORT_THREADS;
 
 int sessiond_check_thread_quit_pipe(int fd, uint32_t events)
 {
@@ -365,10 +366,21 @@ LTTNG_HIDDEN
 void sessiond_notify_ready(void)
 {
 	/*
-	 * The _return variant is used since the implied memory barriers are
-	 * required.
+	 * This memory barrier is paired with the one performed by
+	 * the client thread after it has seen that 'lttng_sessiond_ready' is 0.
+	 *
+	 * The purpose of these memory barriers is to ensure that all
+	 * initialization operations of the various threads that call this
+	 * function to signal that they are ready are commited/published
+	 * before the client thread can see the 'lttng_sessiond_ready' counter
+	 * reach 0.
+	 *
+	 * Note that this could be a 'write' memory barrier, but a full barrier
+	 * is used in case the code using this utility changes. The performance
+	 * implications of this choice are minimal since this is a slow path.
 	 */
-	(void) uatomic_sub_return(&lttng_sessiond_ready, 1);
+	cmm_smp_mb();
+	uatomic_sub(&lttng_sessiond_ready, 1);
 }
 
 static
@@ -4562,8 +4574,17 @@ static void *thread_manage_clients(void *data)
 		if (ret > 0 || (ret < 0 && errno != EINTR)) {
 			goto exit;
 		}
-		cmm_smp_rmb();
 	}
+	/*
+	 * This barrier is paired with the one in sessiond_notify_ready() to
+	 * ensure that loads accessing data initialized by the other threads,
+	 * on which this thread was waiting, are not performed before this point.
+	 *
+	 * Note that this could be a 'read' memory barrier, but a full barrier
+	 * is used in case the code changes. The performance implications of
+	 * this choice are minimal since this is a slow path.
+	 */
+	cmm_smp_mb();
 
 	/* This testpoint is after we signal readiness to the parent. */
 	if (testpoint(sessiond_thread_manage_clients)) {