scsi: fix failing unload of a LLDD module

euler inclusion
category: bugfix
bugzilla: 8990
CVE: NA

---------------------------

This reverts part of commit cff549e4 ("scsi: proper state checking
and module refcount handling in scsi_device_get").

scsi_device_get() will fail in a module exit route, thus device
can't be removed.
Turn try_module_get() into __module_get() to make sure scsi device
will be removed normally.
Signed-off-by: NWei Fang <fangwei1@huawei.com>
Signed-off-by: NHanjun Guo <guohanjun@huawei.com>
[yan: cherry-picked from kernel-4.1 f94b5b901110]
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Reviewed-by: Nzhengbin <zhengbin13@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/scsi/scsi.c

@@ -544,9 +544,6 @@ EXPORT_SYMBOL(scsi_report_opcode);
  * Description: Gets a reference to the scsi_device and increments the use count
  * of the underlying LLDD module.  You must hold host_lock of the
  * parent Scsi_Host or already have a reference when calling this.
- *
- * This will fail if a device is deleted or cancelled, or when the LLD module
- * is in the process of being unloaded.
  */
 int scsi_device_get(struct scsi_device *sdev)
 {
@@ -554,12 +551,12 @@ int scsi_device_get(struct scsi_device *sdev)
 		goto fail;
 	if (!get_device(&sdev->sdev_gendev))
 		goto fail;
-	if (!try_module_get(sdev->host->hostt->module))
-		goto fail_put_device;
+	/* We can fail try_module_get if we're doing SCSI operations
+	 * from module exit (like cache flush)
+	 */
+	__module_get(sdev->host->hostt->module);
 	return 0;
 
-fail_put_device:
-	put_device(&sdev->sdev_gendev);
 fail:
 	return -ENXIO;
 }