[SCSI] scsi_dh: Reference count scsi_dh_attach

Problem reported: http://marc.info/?l=dm-devel&m=124585978305866&w=2

scsi_dh does not do a refernce count for attach/detach, and this affects
the way it is supposed to work with multipath when a device is not
in the dev_list of the hardware handler.

This patch adds a reference count that counts each attach.
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/device_handler/scsi_dh.c

@@ -153,12 +153,24 @@ static int scsi_dh_handler_attach(struct scsi_device *sdev,
 	if (sdev->scsi_dh_data) {
 		if (sdev->scsi_dh_data->scsi_dh != scsi_dh)
 			err = -EBUSY;
-	} else if (scsi_dh->attach)
+		else
+			kref_get(&sdev->scsi_dh_data->kref);
+	} else if (scsi_dh->attach) {
 		err = scsi_dh->attach(sdev);
-
+		if (!err) {
+			kref_init(&sdev->scsi_dh_data->kref);
+			sdev->scsi_dh_data->sdev = sdev;
+		}
+	}
 	return err;
 }
 
+static void __detach_handler (struct kref *kref)
+{
+	struct scsi_dh_data *scsi_dh_data = container_of(kref, struct scsi_dh_data, kref);
+	scsi_dh_data->scsi_dh->detach(scsi_dh_data->sdev);
+}
+
 /*
  * scsi_dh_handler_detach - Detach a device handler from a device
  * @sdev - SCSI device the device handler should be detached from
@@ -180,7 +192,7 @@ static void scsi_dh_handler_detach(struct scsi_device *sdev,
 		scsi_dh = sdev->scsi_dh_data->scsi_dh;
 
 	if (scsi_dh && scsi_dh->detach)
-		scsi_dh->detach(sdev);
+		kref_put(&sdev->scsi_dh_data->kref, __detach_handler);
 }
 
 /*
@@ -474,7 +486,6 @@ int scsi_dh_attach(struct request_queue *q, const char *name)
 
 	if (!err) {
 		err = scsi_dh_handler_attach(sdev, scsi_dh);
-
 		put_device(&sdev->sdev_gendev);
 	}
 	return err;
@@ -505,10 +516,8 @@ void scsi_dh_detach(struct request_queue *q)
 		return;
 
 	if (sdev->scsi_dh_data) {
-		/* if sdev is not on internal list, detach */
 		scsi_dh = sdev->scsi_dh_data->scsi_dh;
-		if (!device_handler_match(scsi_dh, sdev))
-			scsi_dh_handler_detach(sdev, scsi_dh);
+		scsi_dh_handler_detach(sdev, scsi_dh);
 	}
 	put_device(&sdev->sdev_gendev);
 }

include/scsi/scsi_device.h

@@ -191,6 +191,8 @@ struct scsi_device_handler {
 
 struct scsi_dh_data {
 	struct scsi_device_handler *scsi_dh;
+	struct scsi_device *sdev;
+	struct kref kref;
 	char buf[0];
 };