s390/dasd: Fix locking issue when changing EER attribute

The reference to a device in question may get lost when the extended
error reporting (EER) attribute is being enabled/disabled while the
device is set offline at the same time. This is due to missing
refcounting and incorrect locking. Fix this by the following:

- In dasd_eer_store() get the device directly and handle the refcount
  accordingly.
- Move the lock in dasd_eer_enable() up so we can ensure safe
  processing.
- Check if the device is being set offline and return with -EBUSY if so.
- While at it, change the return code from -EPERM to -EMEDIUMTYPE as
  suggested by a FIXME, since that is what we're actually checking.
Reviewed-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dasd_devmap.c

@@ -1167,26 +1167,25 @@ static ssize_t
 dasd_eer_store(struct device *dev, struct device_attribute *attr,
 	       const char *buf, size_t count)
 {
-	struct dasd_devmap *devmap;
+	struct dasd_device *device;
 	unsigned int val;
-	int rc;
+	int rc = 0;
 
-	devmap = dasd_devmap_from_cdev(to_ccwdev(dev));
-	if (IS_ERR(devmap))
-		return PTR_ERR(devmap);
-	if (!devmap->device)
-		return -ENODEV;
+	device = dasd_device_from_cdev(to_ccwdev(dev));
+	if (IS_ERR(device))
+		return PTR_ERR(device);
 
 	if (kstrtouint(buf, 0, &val) || val > 1)
 		return -EINVAL;
 
-	if (val) {
-		rc = dasd_eer_enable(devmap->device);
-		if (rc)
-			return rc;
-	} else
-		dasd_eer_disable(devmap->device);
-	return count;
+	if (val)
+		rc = dasd_eer_enable(device);
+	else
+		dasd_eer_disable(device);
+
+	dasd_put_device(device);
+
+	return rc ? : count;
 }
 
 static DEVICE_ATTR(eer_enabled, 0644, dasd_eer_show, dasd_eer_store);

drivers/s390/block/dasd_eer.c

@@ -454,20 +454,30 @@ static void dasd_eer_snss_cb(struct dasd_ccw_req *cqr, void *data)
  */
 int dasd_eer_enable(struct dasd_device *device)
 {
-	struct dasd_ccw_req *cqr;
+	struct dasd_ccw_req *cqr = NULL;
 	unsigned long flags;
 	struct ccw1 *ccw;
+	int rc = 0;
 
+	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 	if (device->eer_cqr)
-		return 0;
+		goto out;
+	else if (!device->discipline ||
+		 strcmp(device->discipline->name, "ECKD"))
+		rc = -EMEDIUMTYPE;
+	else if (test_bit(DASD_FLAG_OFFLINE, &device->flags))
+		rc = -EBUSY;
 
-	if (!device->discipline || strcmp(device->discipline->name, "ECKD"))
-		return -EPERM;	/* FIXME: -EMEDIUMTYPE ? */
+	if (rc)
+		goto out;
 
 	cqr = dasd_kmalloc_request(DASD_ECKD_MAGIC, 1 /* SNSS */,
 				   SNSS_DATA_SIZE, device);
-	if (IS_ERR(cqr))
-		return -ENOMEM;
+	if (IS_ERR(cqr)) {
+		rc = -ENOMEM;
+		cqr = NULL;
+		goto out;
+	}
 
 	cqr->startdev = device;
 	cqr->retries = 255;
@@ -485,15 +495,18 @@ int dasd_eer_enable(struct dasd_device *device)
 	cqr->status = DASD_CQR_FILLED;
 	cqr->callback = dasd_eer_snss_cb;
 
-	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 	if (!device->eer_cqr) {
 		device->eer_cqr = cqr;
 		cqr = NULL;
 	}
+
+out:
 	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
+
 	if (cqr)
 		dasd_kfree_request(cqr, device);
-	return 0;
+
+	return rc;
 }
 
 /*