linux-kernel - Re: [PATCH net] devlink: rate: Unset parent pointer in devl_rate_nodes

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Message-ID: <d751e671-9b73-42ce-acce-c98947b632c2@nvidia.com>
Date: Thu, 13 Nov 2025 10:33:09 +0200
From: Shay Drori <shayd@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>, Tariq Toukan <tariqt@...dia.com>
CC: Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>,
	Jiri Pirko <jiri@...nulli.us>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Mark Bloch <mbloch@...dia.com>, Gal Pressman
	<gal@...dia.com>, Leon Romanovsky <leonro@...dia.com>, Cosmin Ratiu
	<cratiu@...dia.com>, Moshe Shemesh <moshe@...dia.com>, Jiri Pirko
	<jiri@...dia.com>, Carolina Jubran <cjubran@...dia.com>
Subject: Re: [PATCH net] devlink: rate: Unset parent pointer in
 devl_rate_nodes_destroy



On 13/11/2025 4:12, Jakub Kicinski wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Tue, 11 Nov 2025 14:14:39 +0200 Tariq Toukan wrote:
>> The function devl_rate_nodes_destroy is documented to "Unset parent for
>> all rate objects". However, it was only calling the driver-specific
>> `rate_leaf_parent_set` or `rate_node_parent_set` ops and decrementing
>> the parent's refcount, without actually setting the
>> `devlink_rate->parent` pointer to NULL.
>>
>> This leaves a dangling pointer in the `devlink_rate` struct, which is
>> inconsistent with the behavior of `devlink_nl_rate_parent_node_set`,
>> where the parent pointer is correctly cleared.
>>
>> This patch fixes the issue by explicitly setting `devlink_rate->parent`
>> to NULL after notifying the driver, thus fulfilling the function's
>> documented behavior for all rate objects.
> 
> What is the _real_ issue you're solving here? If the function destroys
> all nodes maybe it doesn't matter that the pointer isn't cleared.
> --
> pw-bot: cr

The problem is a leaf which have this node as a parent, now pointing to
invalid memory. When this leaf will be destroyed, in
devl_rate_leaf_destroy, we can get NULL-ptr error, or refcount error.

Is this answer your question?