[PATCH v2] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[PATCH v2] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[Yazen Ghannam]

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.

Finally, drop the redundant "root = NULL" before the second search
loop. The pci_get_class() iterator always decrements the refcount of
its "from" argument, so the first loop can only fall through with
"root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Reported-by: Sashiko <sashiko-bot@kernel.org>
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@amd.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
Link:
https://lore.kernel.org/r/20260824175003.335196-1-yazen.ghannam@amd.com

v1->v2:
* Add SoB from Mario.
* Remove redundant pointer reset.

 arch/x86/kernel/amd_node.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
index 762585775b5a..b7926ba3610a 100644
--- a/arch/x86/kernel/amd_node.c
+++ b/arch/x86/kernel/amd_node.c
@@ -251,7 +251,7 @@ __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;
@@ -262,7 +262,6 @@ 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");
 
@@ -299,14 +298,13 @@ static int __init amd_smn_init(void)
 
 	count = 0;
 	node = 0;
-	root = NULL;
 	while (node < num_nodes && (root = get_next_root(root))) {
 		/* Use one root for each node and skip the rest. */
 		if (count++ % roots_per_node)
 			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: 7755fae2ea370ee914797c5bcca922836a818c3d
-- 
2.43.0

Re: [PATCH v2] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[Serge Hallyn (AMD)]

On Thu, Sep 03, 2026 at 10:43:25AM -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.
> 
> Finally, drop the redundant "root = NULL" before the second search
> loop. The pci_get_class() iterator always decrements the refcount of
> its "from" argument, so the first loop can only fall through with
> "root" already NULL.
> 
> Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> 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@amd.com>
> Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>

Thanks.  FWIW,

> Reviewed-by: Serge Hallyn (AMD) <sergeh@kernel.org>

> ---
> Link:
> https://lore.kernel.org/r/20260824175003.335196-1-yazen.ghannam@amd.com
> 
> v1->v2:
> * Add SoB from Mario.
> * Remove redundant pointer reset.
> 
>  arch/x86/kernel/amd_node.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
> index 762585775b5a..b7926ba3610a 100644
> --- a/arch/x86/kernel/amd_node.c
> +++ b/arch/x86/kernel/amd_node.c
> @@ -251,7 +251,7 @@ __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;
> @@ -262,7 +262,6 @@ 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");
>  
> @@ -299,14 +298,13 @@ static int __init amd_smn_init(void)
>  
>  	count = 0;
>  	node = 0;
> -	root = NULL;
>  	while (node < num_nodes && (root = get_next_root(root))) {
>  		/* Use one root for each node and skip the rest. */
>  		if (count++ % roots_per_node)
>  			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: 7755fae2ea370ee914797c5bcca922836a818c3d
> -- 
> 2.43.0
>