MDEV-26547 fixup: Wait for read completion

buf_load(): Wait for the submitted reads to finish before updating
innodb_buffer_pool_load_status.

storage/innobase/buf/buf0dump.cc

@@ -715,6 +715,10 @@ buf_load()
 
 	ut_free(dump);
 
+	if (i == dump_n) {
+		os_aio_wait_until_no_pending_reads();
+	}
+
 	ut_sprintf_timestamp(now);
 
 	if (i == dump_n) {

storage/innobase/include/os0file.h

@@ -1116,6 +1116,10 @@ Only used on FLUSH TABLES...FOR EXPORT. */
 void os_aio_wait_until_no_pending_writes();
 
 
+/** Wait until there are no pending asynchronous reads. */
+void os_aio_wait_until_no_pending_reads();
+
+
 /** Prints info of the aio arrays.
 @param[in/out]	file		file where to print */
 void

storage/innobase/os/os0file.cc

@@ -3828,6 +3828,20 @@ void os_aio_wait_until_no_pending_writes()
   buf_dblwr.wait_flush_buffered_writes();
 }
 
+/** Wait until there are no pending asynchronous reads. */
+void os_aio_wait_until_no_pending_reads()
+{
+  const auto notify_wait= read_slots->pending_io_count();
+
+  if (notify_wait)
+    tpool::tpool_wait_begin();
+
+  read_slots->wait();
+
+  if (notify_wait)
+    tpool::tpool_wait_end();
+}
+
 /** Request a read or write.
 @param type		I/O request
 @param buf		buffer