Clean-up: explicit mb before decrementing lttng_sessiond_ready

[lttng-tools.git] / src / bin / lttng-sessiond / main.c

diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index f9b41d2707bd26aff4f95a72aa1885d2f2f09280..9c2458eb1a15a1bee49d1a1babe3d0390418390e 100644 (file)
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -366,10 +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