lightnvm: prevent gennvm module unload on use

After the gennvm module has been initialized. It might be attached to
one or several devices. In that case, the module is in use. Make sure
that it can not be unloaded.
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/lightnvm/gennvm.c

@@ -219,6 +219,9 @@ static int gennvm_register(struct nvm_dev *dev)
 	struct gen_nvm *gn;
 	int ret;
 
+	if (!try_module_get(THIS_MODULE))
+		return -ENODEV;
+
 	gn = kzalloc(sizeof(struct gen_nvm), GFP_KERNEL);
 	if (!gn)
 		return -ENOMEM;
@@ -242,12 +245,14 @@ static int gennvm_register(struct nvm_dev *dev)
 	return 1;
 err:
 	gennvm_free(dev);
+	module_put(THIS_MODULE);
 	return ret;
 }
 
 static void gennvm_unregister(struct nvm_dev *dev)
 {
 	gennvm_free(dev);
+	module_put(THIS_MODULE);
 }
 
 static struct nvm_block *gennvm_get_blk(struct nvm_dev *dev,