On Fri, Feb 07, 2025 at 09:31:09AM +0800, Zhang Zekun wrote: > There are many drivers use of_find_node_by_name() with a not-NULL > device_node pointer, and a number of callers would require a call to > of_node_get() before using it. There are also some drivers who forget > to call of_node_get() which would cause a ref count leak[1]. So, Add a > wraper function for of_find_node_by_name(), drivers may use this function > to call of_find_node_by_name() with the refcount already balanced. > > [1] https://lore.kernel.org/all/20241024015909.58654-1-zhangzekun11@xxxxxxxxxx/ Hi Zhang Zekun, thank you for working on this issue! First of all, let's take a step back and analyze the initial problem. Everything following is only my opinion... The main issue I see is that the current API - of_find_node_by_name - modifies the refcount of its input by calling of_node_put(from) as part of its search. Typically, a "find" function is expected to treat its input as read-only. That is, when you pass an object into such a function, you expect its reference count to remain unchanged unless ownership is explicitly transferred. In this case, lowering the refcount on the input node is counterintuitive and already lead to unexpected behavior and subtle bugs. To address this, the workaround introduces a wrapper function, of_find_node_by_name_balanced, which first increments the input’s refcount (via of_node_get()) before calling the original function. While this "balances" the refcount change, the naming remains problematic from my perspective. The "_balanced" suffix isn’t part of our common naming conventions (traditions? :)). Most drivers expect that a function starting with "find" will not alter the reference count of its input. The term "balanced" doesn’t clearly convey that the input's refcount is being explicitly managed - it instead obscures the underlying behavior, leaving many developers confused about what guarantees the API provides. In my view, a more natural solution would be to redesign the API so that it doesn’t modify the input object’s refcount at all. Instead, it should solely increase the refcount of the returned node (if found) for safe asynchronous usage. This approach would align with established conventions where "find" implies no side effects on inputs or output, and a "get" indicates that the output comes with an extra reference. For example, a function named of_get_node_by_name would clearly signal that only the returned node is subject to a refcount increase while leaving the input intact. Thus, while the current workaround "balances" the reference count, it doesn't address the underlying design flaw. The naming still suggests a "find" function that should leave the input untouched, which isn’t the case here. A redesign of the API - with both the behavior and naming aligned to common expectations - would be a clearer and more robust solution. Nevertheless, it is only my POV, and the final decision rests with the OpenFirmware framework maintainers. Best Regards, Oleksij -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
