[PATCH v7 18/27] scsi-multipath: failover handling

[John Garry <john.g.garry@oracle.com>]

From: John Garry <john.garry@linux.dev>

Failover occurs when the scsi_cmnd has failed and it is discovered that the
target scsi_device has transport down.

For a scsi command which suffers failover, requeue the master bio of each
bio attached to its request.

A bio which for which failover occurs is handled in
scsi_mpath_clone_end_io(). Failover is detected for blk_path_error()
occuring, same as how dm-mpath detects this.

Signed-off-by: John Garry <john.garry@linux.dev>
---
 drivers/scsi/scsi_multipath.c | 39 +++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
index 456351fee4b98..fd28667792472 100644
--- a/drivers/scsi/scsi_multipath.c
+++ b/drivers/scsi/scsi_multipath.c
@@ -256,10 +256,49 @@ void scsi_mpath_dev_clear_path(struct scsi_mpath_device *scsi_mpath_dev)
                mpath_synchronize(mpath_head);
 }
 
+static inline void bio_list_add_clone(struct bio_list *bl,
+				struct bio *clone)
+{
+	struct bio *master_bio = clone->bi_private;
+
+	if (bl->tail)
+		bl->tail->bi_next = master_bio;
+	else
+		bl->head = master_bio;
+	bl->tail = master_bio;
+	bio_put(clone);
+}
+
 static void scsi_mpath_clone_end_io(struct bio *clone)
 {
 	struct bio *master_bio = clone->bi_private;
 
+	if (clone->bi_status && blk_path_error(clone->bi_status)) {
+		struct block_device *bi_bdev = clone->bi_bdev;
+		struct request_queue *q = bi_bdev->bd_queue;
+		struct scsi_device *sdev = scsi_device_from_queue(q);
+		struct scsi_mpath_device *scsi_mpath_dev;
+		struct mpath_device *mpath_device;
+		struct mpath_head *mpath_head;
+		unsigned long flags;
+
+		if (!sdev)
+			goto end_bio;
+
+		scsi_mpath_dev = sdev->scsi_mpath_dev;
+		mpath_device = &scsi_mpath_dev->mpath_device;
+		mpath_head = mpath_device->mpath_head;
+
+		spin_lock_irqsave(&mpath_head->requeue_lock, flags);
+		bio_list_add_clone(&mpath_head->requeue_list, clone);
+		spin_unlock_irqrestore(&mpath_head->requeue_lock, flags);
+
+		mpath_schedule_requeue_work(mpath_head);
+		put_device(&sdev->sdev_gendev);
+		return;
+	}
+
+end_bio:
 	master_bio->bi_status = clone->bi_status;
 	bio_put(clone);
 	bio_endio(master_bio);
-- 
2.43.7