[RFC PATCH 3/3] scsi, usb: storage: Complete the blk-request directly.

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The usb-storage driver runs in a thread and completes its request from
that thread. Since it is a single queued device it always schedules
ksoftirqd for its completion.

The completion is performed in the SCSI stack. Add
scsi_done_preemptible() which inlines most of scsi_mq_done() and
completes the request directly via blk_mq_complete_request_direct().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 drivers/scsi/scsi_lib.c   | 17 ++++++++++++++++-
 drivers/usb/storage/usb.c |  2 +-
 include/scsi/scsi_cmnd.h  |  7 +++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 572673873ddf8..f0eeedce6b081 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1575,16 +1575,31 @@ static blk_status_t scsi_prepare_cmd(struct request *req)
 	return scsi_cmd_to_driver(cmd)->init_command(cmd);
 }
 
-static void scsi_mq_done(struct scsi_cmnd *cmd)
+static void _scsi_mq_done(struct scsi_cmnd *cmd)
 {
 	if (unlikely(blk_should_fake_timeout(scsi_cmd_to_rq(cmd)->q)))
 		return;
 	if (unlikely(test_and_set_bit(SCMD_STATE_COMPLETE, &cmd->state)))
 		return;
 	trace_scsi_dispatch_cmd_done(cmd);
+}
+
+static void scsi_mq_done(struct scsi_cmnd *cmd)
+{
+	_scsi_mq_done(cmd);
 	blk_mq_complete_request(scsi_cmd_to_rq(cmd));
 }
 
+void scsi_done_preemptible(struct scsi_cmnd *scmd)
+{
+	if (scmd->scsi_done != scsi_mq_done) {
+		scmd->scsi_done(scmd);
+		return;
+	}
+	_scsi_mq_done(scmd);
+	blk_mq_complete_request_direct(scsi_cmd_to_rq(scmd));
+}
+
 static void scsi_mq_put_budget(struct request_queue *q, int budget_token)
 {
 	struct scsi_device *sdev = q->queuedata;
diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
index 90aa9c12ffac5..6ceedd1e14ce7 100644
--- a/drivers/usb/storage/usb.c
+++ b/drivers/usb/storage/usb.c
@@ -417,7 +417,7 @@ static int usb_stor_control_thread(void * __us)
 		if (srb) {
 			usb_stor_dbg(us, "scsi cmd done, result=0x%x\n",
 					srb->result);
-			srb->scsi_done(srb);
+			scsi_done_preemptible(srb);
 		}
 	} /* for (;;) */
 
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index eaf04c9a1dfcb..e992f2f74dd69 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -396,4 +396,11 @@ static inline unsigned scsi_transfer_length(struct scsi_cmnd *scmd)
 extern void scsi_build_sense(struct scsi_cmnd *scmd, int desc,
 			     u8 key, u8 asc, u8 ascq);
 
+static inline void scsi_done(struct scsi_cmnd *scmd)
+{
+	scmd->scsi_done(scmd);
+}
+
+extern void scsi_done_preemptible(struct scsi_cmnd *scmd);
+
 #endif /* _SCSI_SCSI_CMND_H */
-- 
2.33.0




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