MDEV-21501 Innodb AIO: release IO slots early in io_callback

prevent potential stalls for when all slots are used up, and all io threads
are used up, and io callbacks are slow.

storage/innobase/fil/fil0fil.cc

@@ -4184,15 +4184,13 @@ fil_io(
 /**********************************************************************/
 
 /** Callback for AIO completion */
-void fil_aio_callback(const tpool::aiocb *cb)
+void fil_aio_callback(os_aio_userdata_t *data)
 {
-	os_aio_userdata_t *data=(os_aio_userdata_t *)cb->m_userdata;
 	fil_node_t* node= data->node;
 	void* message = data->message;
 
 	ut_ad(fil_validate_skip());
 
-	ut_a(cb->m_err == DB_SUCCESS);
 
 	if (node == NULL) {
 		ut_ad(srv_shutdown_state == SRV_SHUTDOWN_EXIT_THREADS);

storage/innobase/os/os0file.cc

@@ -3872,12 +3872,12 @@ os_file_get_status(
 }
 
 
-extern void fil_aio_callback(const tpool::aiocb *cb);
+extern void fil_aio_callback(os_aio_userdata_t *data);
 
 static void io_callback(tpool::aiocb* cb)
 {
-	fil_aio_callback(cb);
-
+	ut_a(cb->m_err == DB_SUCCESS);
+	os_aio_userdata_t data = *(os_aio_userdata_t*)cb->m_userdata;
 	/* Return cb back to cache*/
 	if (cb->m_opcode == tpool::aio_opcode::AIO_PREAD) {
 		if (read_slots->contains(cb)) {
@@ -3890,6 +3890,8 @@ static void io_callback(tpool::aiocb* cb)
 		ut_ad(write_slots->contains(cb));
 		write_slots->release(cb);
 	}
+
+	fil_aio_callback(&data);
 }
 
 #ifdef LINUX_NATIVE_AIO