[PATCH] PCI: kirin: Fix of_node_put() issue in pcie-kirin

[PATCH] PCI: kirin: Fix of_node_put() issue in pcie-kirin

[Wan Jiabing]

Fix following coccicheck warning:
./drivers/pci/controller/dwc/pcie-kirin.c:414:2-34: WARNING: Function
for_each_available_child_of_node should have of_node_put() before return.

Early exits from for_each_available_child_of_node should decrement the
node reference counter. Replace return by goto here.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
---
 drivers/pci/controller/dwc/pcie-kirin.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-kirin.c b/drivers/pci/controller/dwc/pcie-kirin.c
index 06017e826832..23a2c076ce53 100644
--- a/drivers/pci/controller/dwc/pcie-kirin.c
+++ b/drivers/pci/controller/dwc/pcie-kirin.c
@@ -422,7 +422,8 @@ static int kirin_pcie_parse_port(struct kirin_pcie *pcie,
 			pcie->num_slots++;
 			if (pcie->num_slots > MAX_PCI_SLOTS) {
 				dev_err(dev, "Too many PCI slots!\n");
-				return -EINVAL;
+				ret = -EINVAL;
+				goto put_node;
 			}
 
 			ret = of_pci_get_devfn(child);
-- 
2.20.1

Re: [PATCH] PCI: kirin: Fix of_node_put() issue in pcie-kirin

[Bjorn Helgaas]

[+to Mauro, author of code being changed,
Rob for "of_pci_get_devfn()" naming question]

On Wed, Nov 03, 2021 at 02:25:18AM -0400, Wan Jiabing wrote:
> Fix following coccicheck warning:
> ./drivers/pci/controller/dwc/pcie-kirin.c:414:2-34: WARNING: Function
> for_each_available_child_of_node should have of_node_put() before return.
> 
> Early exits from for_each_available_child_of_node should decrement the
> node reference counter. Replace return by goto here.
> 
> Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
> ---
>  drivers/pci/controller/dwc/pcie-kirin.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-kirin.c b/drivers/pci/controller/dwc/pcie-kirin.c
> index 06017e826832..23a2c076ce53 100644
> --- a/drivers/pci/controller/dwc/pcie-kirin.c
> +++ b/drivers/pci/controller/dwc/pcie-kirin.c
> @@ -422,7 +422,8 @@ static int kirin_pcie_parse_port(struct kirin_pcie *pcie,
>  			pcie->num_slots++;
>  			if (pcie->num_slots > MAX_PCI_SLOTS) {
>  				dev_err(dev, "Too many PCI slots!\n");
> -				return -EINVAL;
> +				ret = -EINVAL;
> +				goto put_node;
>  			}
>  
>  			ret = of_pci_get_devfn(child);

This is a change to the code added here:
  https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?id=31bd24f0cfe0

This fix looks right to me; all the other early exits from the inner
loop drop the "child" reference.

But this is a nested loop and the *outer* loop also increments
refcounts, and I don't see that outer loop reference on "parent" being
dropped at all:

    for_each_available_child_of_node(node, parent) { 
      for_each_available_child_of_node(parent, child) {
	...
	if (error)
	  goto put_node;
      }
    }

  put_node:
    of_node_put(child);

The "of_pci_get_devfn()" immediately after is unrelated, but possibly
a confusing name.  "Get" often suggests a reference count being
increased, but that's not the case with of_pci_get_devfn().

I want to fix this before sending a pull request to Linus, and I can
easily squash it into a local branch, but I need an ack from Mauro
that this patch is correct and also a fix or explanation for the outer
loop reference situation.

Bjorn

Re: [PATCH] PCI: kirin: Fix of_node_put() issue in pcie-kirin

[Rob Herring]

On Wed, Nov 3, 2021 at 9:31 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> [+to Mauro, author of code being changed,
> Rob for "of_pci_get_devfn()" naming question]
>
> On Wed, Nov 03, 2021 at 02:25:18AM -0400, Wan Jiabing wrote:
> > Fix following coccicheck warning:
> > ./drivers/pci/controller/dwc/pcie-kirin.c:414:2-34: WARNING: Function
> > for_each_available_child_of_node should have of_node_put() before return.
> >
> > Early exits from for_each_available_child_of_node should decrement the
> > node reference counter. Replace return by goto here.
> >
> > Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-kirin.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-kirin.c b/drivers/pci/controller/dwc/pcie-kirin.c
> > index 06017e826832..23a2c076ce53 100644
> > --- a/drivers/pci/controller/dwc/pcie-kirin.c
> > +++ b/drivers/pci/controller/dwc/pcie-kirin.c
> > @@ -422,7 +422,8 @@ static int kirin_pcie_parse_port(struct kirin_pcie *pcie,
> >                       pcie->num_slots++;
> >                       if (pcie->num_slots > MAX_PCI_SLOTS) {
> >                               dev_err(dev, "Too many PCI slots!\n");
> > -                             return -EINVAL;
> > +                             ret = -EINVAL;
> > +                             goto put_node;
> >                       }
> >
> >                       ret = of_pci_get_devfn(child);
>
> This is a change to the code added here:
>   https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?id=31bd24f0cfe0
>
> This fix looks right to me; all the other early exits from the inner
> loop drop the "child" reference.
>
> But this is a nested loop and the *outer* loop also increments
> refcounts, and I don't see that outer loop reference on "parent" being
> dropped at all:
>
>     for_each_available_child_of_node(node, parent) {
>       for_each_available_child_of_node(parent, child) {
>         ...
>         if (error)
>           goto put_node;
>       }
>     }
>
>   put_node:
>     of_node_put(child);

Indeed. There should be a put on the parent.

This whole function is less than ideal as it assumes the board has 2
levels of PCI nodes. This might be another (like brcmstb thread) place
to use .add_bus(). But that's a problem for another day.

> The "of_pci_get_devfn()" immediately after is unrelated, but possibly
> a confusing name.  "Get" often suggests a reference count being
> increased, but that's not the case with of_pci_get_devfn().

I guess you have to know that only nodes are refcounted and property
functions never are.

There's also of_pci_get_max_link_speed() and of_get_pci_domain_nr().

Rob

Re: [PATCH] PCI: kirin: Fix of_node_put() issue in pcie-kirin

[Jiabing Wan]

On 2021/11/4 21:56, Rob Herring wrote:
> On Wed, Nov 3, 2021 at 9:31 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>> [+to Mauro, author of code being changed,
>> Rob for "of_pci_get_devfn()" naming question]
>>
>> On Wed, Nov 03, 2021 at 02:25:18AM -0400, Wan Jiabing wrote:
>>> Fix following coccicheck warning:
>>> ./drivers/pci/controller/dwc/pcie-kirin.c:414:2-34: WARNING: Function
>>> for_each_available_child_of_node should have of_node_put() before return.
>>>
>>> Early exits from for_each_available_child_of_node should decrement the
>>> node reference counter. Replace return by goto here.
>>>
>>> Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
>>> ---
>>>   drivers/pci/controller/dwc/pcie-kirin.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/pci/controller/dwc/pcie-kirin.c b/drivers/pci/controller/dwc/pcie-kirin.c
>>> index 06017e826832..23a2c076ce53 100644
>>> --- a/drivers/pci/controller/dwc/pcie-kirin.c
>>> +++ b/drivers/pci/controller/dwc/pcie-kirin.c
>>> @@ -422,7 +422,8 @@ static int kirin_pcie_parse_port(struct kirin_pcie *pcie,
>>>                        pcie->num_slots++;
>>>                        if (pcie->num_slots > MAX_PCI_SLOTS) {
>>>                                dev_err(dev, "Too many PCI slots!\n");
>>> -                             return -EINVAL;
>>> +                             ret = -EINVAL;
>>> +                             goto put_node;
>>>                        }
>>>
>>>                        ret = of_pci_get_devfn(child);
>> This is a change to the code added here:
>>    https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?id=31bd24f0cfe0
>>
>> This fix looks right to me; all the other early exits from the inner
>> loop drop the "child" reference.
>>
>> But this is a nested loop and the *outer* loop also increments
>> refcounts, and I don't see that outer loop reference on "parent" being
>> dropped at all:
>>
>>      for_each_available_child_of_node(node, parent) {
>>        for_each_available_child_of_node(parent, child) {
>>          ...
>>          if (error)
>>            goto put_node;
>>        }
>>      }
>>
>>    put_node:
>>      of_node_put(child);
> Indeed. There should be a put on the parent.
OK, I'll fix in v2. Thanks.

Jiabing Wan