pcie aspm link setup, grandparent instead of parent?

pcie aspm link setup, grandparent instead of parent?

[Radim Krčmář]

Hello,

as a consequence of hitting a NULL dereference bug[1] while downstream
aspm is setting up link_state, I started to wonder why is the code
skipping its parent bus in favour of grandparent's link_state.[2]

Is this right? (I have no device to test on ...)

Thanks.

---
1: https://bugzilla.redhat.com/show_bug.cgi?id=972381
   The bug is hit because "pdev->bus->parent" has NULL "->parent" and thus
   NULL "->self".
2: "pdev = bus->self", so "pdev->bus->parent == bus->parent->parent"


diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 403a443..d58e282 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -527,7 +527,7 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
 	link->pdev = pdev;
 	if (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM) {
 		struct pcie_link_state *parent;
-		parent = pdev->bus->parent->self->link_state;
+		parent = pdev->bus->self->link_state;
 		if (!parent) {
 			kfree(link);
 			return NULL;

Re: pcie aspm link setup, grandparent instead of parent?

[Bjorn Helgaas]

[+cc linux-pci, Myron, Joe]

On Wed, Jun 12, 2013 at 11:21 AM, Radim Krčmář <rkrcmar@redhat.com> wrote:
> Hello,
>
> as a consequence of hitting a NULL dereference bug[1] while downstream
> aspm is setting up link_state, I started to wonder why is the code
> skipping its parent bus in favour of grandparent's link_state.[2]
>
> Is this right? (I have no device to test on ...)
>
> Thanks.
>
> ---
> 1: https://bugzilla.redhat.com/show_bug.cgi?id=972381
>    The bug is hit because "pdev->bus->parent" has NULL "->parent" and thus
>    NULL "->self".
> 2: "pdev = bus->self", so "pdev->bus->parent == bus->parent->parent"
>
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 403a443..d58e282 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -527,7 +527,7 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
>         link->pdev = pdev;
>         if (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM) {
>                 struct pcie_link_state *parent;
> -               parent = pdev->bus->parent->self->link_state;
> +               parent = pdev->bus->self->link_state;
>                 if (!parent) {
>                         kfree(link);
>                         return NULL;
> --
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Re: pcie aspm link setup, grandparent instead of parent?

[Radim Krčmář]

2013-06-12 15:54-0600, Bjorn Helgaas:
> [+cc linux-pci, Myron, Joe]

I'll remember it.

> On Wed, Jun 12, 2013 at 11:21 AM, Radim Krčmář <rkrcmar@redhat.com> wrote:
> > Hello,
> >
> > as a consequence of hitting a NULL dereference bug[1] while downstream
> > aspm is setting up link_state, I started to wonder why is the code
> > skipping its parent bus in favour of grandparent's link_state.[2]
> >
> > Is this right? (I have no device to test on ...)

No,
pcie_link_state covers both upstream and downstream port, so we skip
upstream port of current device.

Must the "parent device" (grandparent) have valid "->self"?
(qemu allows even topologies without the upstream port, so it does not
count for much ...)

> > Thanks.
> >
> > ---
> > 1: https://bugzilla.redhat.com/show_bug.cgi?id=972381
> >    The bug is hit because "pdev->bus->parent" has NULL "->parent" and thus
> >    NULL "->self".
> > 2: "pdev = bus->self", so "pdev->bus->parent == bus->parent->parent"
> >
> >
> > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > index 403a443..d58e282 100644
> > --- a/drivers/pci/pcie/aspm.c
> > +++ b/drivers/pci/pcie/aspm.c
> > @@ -527,7 +527,7 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
> >         link->pdev = pdev;
> >         if (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM) {
> >                 struct pcie_link_state *parent;
> > -               parent = pdev->bus->parent->self->link_state;
> > +               parent = pdev->bus->self->link_state;
> >                 if (!parent) {
> >                         kfree(link);
> >                         return NULL;