Re:Re: [PATCH] powerpc: kernel: pci_dn: Add missing of_node_put() for of_get_xx API

At 2022-07-02 03:47:22, "Tyrel Datwyler" [off-list ref] wrote:

On 7/1/22 06:17, Liang He wrote:

quoted

In pci_add_device_node_info(), we should use of_node_put() for the
reference 'parent' returned by of_get_parent() to keep refcount
balance.

Fixes: cca87d303c85 ("powerpc/pci: Refactor pci_dn")
Co-authored-by: Miaoqian Lin [off-list ref]
Signed-off-by: Liang He <redacted>
---
 arch/powerpc/kernel/pci_dn.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/pci_dn.c b/arch/powerpc/kernel/pci_dn.c
index 938ab8838ab5..aa221958007e 100644
--- a/arch/powerpc/kernel/pci_dn.c
+++ b/arch/powerpc/kernel/pci_dn.c

@@ -330,6 +330,7 @@ struct pci_dn *pci_add_device_node_info(struct pci_controller *hose,
 	INIT_LIST_HEAD(&pdn->list);
 	parent = of_get_parent(dn);
 	pdn->parent = parent ? PCI_DN(parent) : NULL;

NACK

pdn->parent is now a long term reference so we should not do a put on parent
until we pdn->parent is no longer valid.

-Tyrel

Hi, Tyrel

Thanks for reviewing this code.

But I think there is some confusion about the of_get_parent() and I can confirm
my point when I check the 'pci_remove_device_node_info' function, which may be
a second bug.

In pci_remove_device_node_info(), I notice the comment, 'Drop the parent pci_dn's ref ...'.
However, of_get_parent() will increase the refcount of the parent, and then the
following of_node_put() will decrease the refcount, so, finally, there is no any change.

Back to this case, as the 'pdn->parent' is not the reference of parent device_node, it is
device_node's data, so I think it is better to keep the original meaning of refcounting, i.e,
add a of_node_put() to keep the refcount balance.

If I have some mis-understanding, please correct me.

Thanks,

Liang

quoted

+	of_node_put(parent);
 	if (pdn->parent)
 		list_add_tail(&pdn->list, &pdn->parent->child_list);