Re: [PATCH] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[Serge Hallyn (AMD)]

On Mon, Aug 24, 2026 at 12:50:03PM -0500, Yazen Ghannam wrote:
> The local "root" pointer is a temporary variable used during the device
> search. Therefore, refcount related to the search iterators should be
> cleaned up after the search is complete.
> 
> Use the __free() cleanup macro to ensure the refcount is decremented
> when the temporary pointer goes out of scope.
> 
> Additionally, increment the refcount when caching a root pointer. This
> ensures the in-use refcount is separate from the temporary search
> refcounting.
> 
> Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
> Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
> Assisted-by: Claude-Code:claude-opus-5
> Signed-off-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>
> ---
>  arch/x86/kernel/amd_node.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
> index 0be01725a2a4..312adf73313b 100644
> --- a/arch/x86/kernel/amd_node.c
> +++ b/arch/x86/kernel/amd_node.c
> @@ -247,7 +247,7 @@ __setup("amd_smn_debugfs_enable", amd_smn_enable_dfs);
>  static int __init amd_smn_init(void)
>  {
>  	u16 count, num_roots, roots_per_node, node, num_nodes;
> -	struct pci_dev *root;
> +	struct pci_dev *root __free(pci_dev_put) = NULL;
>  
>  	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
>  		return 0;
> @@ -258,7 +258,6 @@ static int __init amd_smn_init(void)
>  		return 0;
>  
>  	num_roots = 0;
> -	root = NULL;
>  	while ((root = get_next_root(root))) {
>  		pci_dbg(root, "Reserving PCI config space\n");
>  

Will this leak the ref taken on the last get_next_root(root) in the
first loop?  You might need a pci_dev_put(root) before the root = NULL
above the second loop.  Or I could be wrong.

> @@ -297,7 +296,7 @@ static int __init amd_smn_init(void)
>  			continue;
>  
>  		pci_dbg(root, "is root for AMD node %u\n", node);
> -		amd_roots[node++] = root;
> +		amd_roots[node++] = pci_dev_get(root);
>  	}
>  
>  	if (enable_dfs) {
> 
> base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> -- 
> 2.43.0
>