scsi: core: Add scsi_done_direct() for immediate completion

Add scsi_done_direct() which behaves like scsi_done() except that it
invokes blk_mq_complete_request_direct() in order to complete the request.

Callers from process context can complete the request directly instead
waking ksoftirqd.

Link: https://lore.kernel.org/r/Yfw7JaszshmfYa1d@flowReviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -1625,8 +1625,10 @@ static blk_status_t scsi_prepare_cmd(struct request *req)
 	return scsi_cmd_to_driver(cmd)->init_command(cmd);
 }
 
-void scsi_done(struct scsi_cmnd *cmd)
+static void scsi_done_internal(struct scsi_cmnd *cmd, bool complete_directly)
 {
+	struct request *req = scsi_cmd_to_rq(cmd);
+
 	switch (cmd->submitter) {
 	case SUBMITTED_BY_BLOCK_LAYER:
 		break;
@@ -1641,10 +1643,25 @@ void scsi_done(struct scsi_cmnd *cmd)
 	if (unlikely(test_and_set_bit(SCMD_STATE_COMPLETE, &cmd->state)))
 		return;
 	trace_scsi_dispatch_cmd_done(cmd);
-	blk_mq_complete_request(scsi_cmd_to_rq(cmd));
+
+	if (complete_directly)
+		blk_mq_complete_request_direct(req, scsi_complete);
+	else
+		blk_mq_complete_request(req);
+}
+
+void scsi_done(struct scsi_cmnd *cmd)
+{
+	scsi_done_internal(cmd, false);
 }
 EXPORT_SYMBOL(scsi_done);
 
+void scsi_done_direct(struct scsi_cmnd *cmd)
+{
+	scsi_done_internal(cmd, true);
+}
+EXPORT_SYMBOL(scsi_done_direct);
+
 static void scsi_mq_put_budget(struct request_queue *q, int budget_token)
 {
 	struct scsi_device *sdev = q->queuedata;

include/scsi/scsi_cmnd.h

@@ -168,6 +168,7 @@ static inline struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
 }
 
 void scsi_done(struct scsi_cmnd *cmd);
+void scsi_done_direct(struct scsi_cmnd *cmd);
 
 extern void scsi_finish_command(struct scsi_cmnd *cmd);