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

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Message-ID: <20251113171528.12517f4a@kernel.org>
Date: Thu, 13 Nov 2025 17:15:28 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Shay Drori <shayd@...dia.com>
Cc: Tariq Toukan <tariqt@...dia.com>, 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 Thu, 13 Nov 2025 10:33:09 +0200 Shay Drori wrote:
> > 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.
> 
> 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?

Kind of. I was hoping you can add a concrete example to the commit
message. What sequence of user operations are needed with mlx5 to
make the kernel oops.