Merge remote-tracking branch 'remotes/kraxel/tags/ui-20190313-pull-request' into...

[mirror_qemu.git] / util / rcu.c

diff --git a/util/rcu.c b/util/rcu.c
index f4d09c83044666013a6b44fb571621854f3b0b86..5676c22bd1f571ca521f14a222ae88418b1eeacb 100644 (file)
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -92,10 +92,11 @@ static void wait_for_readers(void)
             atomic_set(&index->waiting, true);
         }
 
-        /* Here, order the stores to index->waiting before the
-         * loads of index->ctr.
+        /* Here, order the stores to index->waiting before the loads of
+         * index->ctr.  Pairs with smp_mb_placeholder() in rcu_read_unlock(),
+         * ensuring that the loads of index->ctr are sequentially consistent.
          */
-        smp_mb();
+        smp_mb_global();
 
         QLIST_FOREACH_SAFE(index, &registry, node, tmp) {
             if (!rcu_gp_ongoing(&index->ctr)) {
@@ -142,8 +143,13 @@ static void wait_for_readers(void)
 void synchronize_rcu(void)
 {
     qemu_mutex_lock(&rcu_sync_lock);
-    qemu_mutex_lock(&rcu_registry_lock);
 
+    /* Write RCU-protected pointers before reading p_rcu_reader->ctr.
+     * Pairs with smp_mb_placeholder() in rcu_read_lock().
+     */
+    smp_mb_global();
+
+    qemu_mutex_lock(&rcu_registry_lock);
     if (!QLIST_EMPTY(&registry)) {
         /* In either case, the atomic_mb_set below blocks stores that free
          * old RCU-protected pointers.
@@ -370,6 +376,7 @@ static void rcu_init_child(void)
 
 static void __attribute__((__constructor__)) rcu_init(void)
 {
+    smp_mb_global_init();
 #ifdef CONFIG_POSIX
     pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_child);
 #endif