1 files changed, 7 insertions, 18 deletions

diff --git a/block.c b/block.c
index 7ea0b82049..b8bab06e55 100644
--- a/block.c
+++ b/block.c
@@ -2855,7 +2855,6 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
 {
     BlockDriverState *old_bs = child->bs;
     int new_bs_quiesce_counter;
-    int drain_saldo;
 
     assert(!child->frozen);
     assert(old_bs != new_bs);
@@ -2865,16 +2864,13 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
         assert(bdrv_get_aio_context(old_bs) == bdrv_get_aio_context(new_bs));
     }
 
-    new_bs_quiesce_counter = (new_bs ? new_bs->quiesce_counter : 0);
-    drain_saldo = new_bs_quiesce_counter - child->parent_quiesce_counter;
-
     /*
      * If the new child node is drained but the old one was not, flush
      * all outstanding requests to the old child node.
      */
-    while (drain_saldo > 0 && child->klass->drained_begin) {
+    new_bs_quiesce_counter = (new_bs ? new_bs->quiesce_counter : 0);
+    if (new_bs_quiesce_counter && !child->quiesced_parent) {
         bdrv_parent_drained_begin_single(child, true);
-        drain_saldo--;
     }
 
     if (old_bs) {
@@ -2890,16 +2886,6 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
     if (new_bs) {
         assert_bdrv_graph_writable(new_bs);
         QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
-
-        /*
-         * Polling in bdrv_parent_drained_begin_single() may have led to the new
-         * node's quiesce_counter having been decreased.  Not a problem, we just
-         * need to recognize this here and then invoke drained_end appropriately
-         * more often.
-         */
-        assert(new_bs->quiesce_counter <= new_bs_quiesce_counter);
-        drain_saldo += new_bs->quiesce_counter - new_bs_quiesce_counter;
-
         if (child->klass->attach) {
             child->klass->attach(child);
         }
@@ -2908,10 +2894,13 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
     /*
      * If the old child node was drained but the new one is not, allow
      * requests to come in only after the new node has been attached.
+     *
+     * Update new_bs_quiesce_counter because bdrv_parent_drained_begin_single()
+     * polls, which could have changed the value.
      */
-    while (drain_saldo < 0 && child->klass->drained_end) {
+    new_bs_quiesce_counter = (new_bs ? new_bs->quiesce_counter : 0);
+    if (!new_bs_quiesce_counter && child->quiesced_parent) {
         bdrv_parent_drained_end_single(child);
-        drain_saldo++;
     }
 }