[PATCH v2 05/20] scsi: core: Add support for internal commands

[Bart Van Assche <bvanassche@xxxxxxx>]

From: Hannes Reinecke <hare@xxxxxxx>

Add helper functions to allow LLDs to allocate and free internal commands.
This patch is based on Hannes' patch with the subject "scsi: add
scsi_{get,put}_internal_cmd() helper".

Cc: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
[ bvanassche: changed type of the first argument of the new functions from
  struct scsi_device * into struct request_queue * and included changes for
  the timeout handlers in this patch. ]
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 drivers/scsi/scsi_error.c  |  7 ++++++
 drivers/scsi/scsi_lib.c    | 46 +++++++++++++++++++++++++++++++++++++-
 include/scsi/scsi_device.h |  4 ++++
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index cd05f2db3339..3703ee9c89dd 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -339,6 +339,13 @@ enum blk_eh_timer_return scsi_times_out(struct request *req)
 	if (test_and_set_bit(SCMD_STATE_COMPLETE, &scmd->state))
 		return BLK_EH_DONE;
 
+	/*
+	 * The code below is for documentation purposes only since the
+	 * dereference above of the scmd->device pointer triggers a kernel
+	 * oops for internal commands.
+	 */
+	WARN_ON_ONCE(blk_rq_is_internal(scsi_cmd_to_rq(scmd)));
+
 	trace_scsi_dispatch_cmd_timeout(scmd);
 	scsi_log_completion(scmd, TIMEOUT_ERROR);
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 621d841d819a..59c3c4fbcfc0 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1756,8 +1756,9 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 static enum blk_eh_timer_return scsi_timeout(struct request *req,
 		bool reserved)
 {
-	if (reserved)
+	if (blk_rq_is_internal(req) || WARN_ON_ONCE(reserved))
 		return BLK_EH_RESET_TIMER;
+
 	return scsi_times_out(req);
 }
 
@@ -1957,6 +1958,49 @@ void scsi_mq_destroy_tags(struct Scsi_Host *shost)
 	blk_mq_free_tag_set(&shost->tag_set);
 }
 
+/**
+ * scsi_get_internal_cmd - Allocate an internal SCSI command
+ * @q: request queue from which to allocate the command. This request queue may
+ *	but does not have to be associated with a SCSI device. This request
+ *	queue must be associated with a SCSI tag set. See also
+ *	scsi_mq_setup_tags().
+ * @data_direction: Data direction for the allocated command.
+ * @flags: Zero or more BLK_MQ_REQ_* flags.
+ *
+ * Allocates a request for driver-internal use. The tag of the returned SCSI
+ * command is guaranteed to be unique.
+ */
+struct scsi_cmnd *scsi_get_internal_cmd(struct request_queue *q,
+					enum dma_data_direction data_direction,
+					blk_mq_req_flags_t flags)
+{
+	unsigned int opf = REQ_INTERNAL;
+	struct request *rq;
+
+	opf |= data_direction == DMA_TO_DEVICE ? REQ_OP_DRV_OUT : REQ_OP_DRV_IN;
+	rq = blk_mq_alloc_request(q, opf, flags);
+	if (IS_ERR(rq))
+		return ERR_CAST(rq);
+	return blk_mq_rq_to_pdu(rq);
+}
+EXPORT_SYMBOL_GPL(scsi_get_internal_cmd);
+
+/**
+ * scsi_put_internal_cmd - Free an internal SCSI command
+ * @scmd: SCSI command to be freed
+ *
+ * Check if @scmd is an internal command and call blk_mq_free_request() if true.
+ */
+void scsi_put_internal_cmd(struct scsi_cmnd *scmd)
+{
+	struct request *rq = blk_mq_rq_from_pdu(scmd);
+
+	if (WARN_ON_ONCE(!blk_rq_is_internal(rq)))
+		return;
+	blk_mq_free_request(rq);
+}
+EXPORT_SYMBOL_GPL(scsi_put_internal_cmd);
+
 /**
  * scsi_device_from_queue - return sdev associated with a request_queue
  * @q: The request queue to return the sdev from
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index d1c6fc83b1e3..348c12274324 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -9,6 +9,7 @@
 #include <scsi/scsi.h>
 #include <linux/atomic.h>
 #include <linux/sbitmap.h>
+#include <linux/dma-direction.h>
 
 struct bsg_device;
 struct device;
@@ -470,6 +471,9 @@ static inline int scsi_execute_req(struct scsi_device *sdev,
 	return scsi_execute(sdev, cmd, data_direction, buffer,
 		bufflen, NULL, sshdr, timeout, retries,  0, 0, resid);
 }
+struct scsi_cmnd *scsi_get_internal_cmd(struct request_queue *q,
+	enum dma_data_direction data_direction, blk_mq_req_flags_t flags);
+void scsi_put_internal_cmd(struct scsi_cmnd *scmd);
 extern void sdev_disable_disk_events(struct scsi_device *sdev);
 extern void sdev_enable_disk_events(struct scsi_device *sdev);
 extern int scsi_vpd_lun_id(struct scsi_device *, char *, size_t);