On Fri, 2014-02-14 at 19:48 +0200, Imre Deak wrote:
> On Fri, 2014-02-14 at 17:35 +0000, Chris Wilson wrote:
> > On Fri, Feb 14, 2014 at 07:23:32PM +0200, Imre Deak wrote:
> > > pci_get_class(class, from) drops the refcount for 'from', so the
> > > extra pci_dev_put we do on it will result in a use after free bug
> > > sometime later starting with the WARN below.
> >
> > That's a very nice find.
> >
> > But you can tidy this loop up even more...
> >
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > > b/drivers/gpu/drm/i915/i915_drv.c
> > > index 2d05d7c..4e4fc0c 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.c
> > > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > > @@ -347,7 +347,6 @@ void intel_detect_pch(struct drm_device *dev)
> > > */
> > > pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> > > while (pch) {
> >
> > ...by noting that what you want here is
> > while ((pch = pci_get_class(ISA<<8, pch)) {
> >
> > > - struct pci_dev *curr = pch;
> > > if (pch->vendor == PCI_VENDOR_ID_INTEL) {
> > > unsigned short id;
> > > id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
> > > @@ -385,15 +384,15 @@ void intel_detect_pch(struct drm_device *dev)
> > > } else {
> > > goto check_next;
> > > }
> > > - pci_dev_put(pch);
> > > break;
> > > }
> > > check_next:
> > > - pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
> > > - pci_dev_put(curr);
> > > + pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, pch);
> > > }
> > > if (!pch)
> > > DRM_DEBUG_KMS("No PCH found?\n");
> > > + else
> > > + pci_dev_put(pch);
> > > }
> >
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > b/drivers/gpu/drm/i915/i915_drv.c
> > index 2d05d7c..9962aef 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -324,7 +324,7 @@ MODULE_DEVICE_TABLE(pci, pciidlist);
> > void intel_detect_pch(struct drm_device *dev)
> > {
> > struct drm_i915_private *dev_priv = dev->dev_private;
> > - struct pci_dev *pch;
> > + struct pci_dev *pch = NULL;
> >
> > /* In all current cases, num_pipes is equivalent to the PCH_NOP setting
> > * (which really amounts to a PCH but no South Display).
> > @@ -345,12 +345,9 @@ void intel_detect_pch(struct drm_device *dev)
> > * all the ISA bridge devices and check for the first match, instead
> > * of only checking the first one.
> > */
> > - pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> > - while (pch) {
> > - struct pci_dev *curr = pch;
> > + while ((pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, pch))) {
> > if (pch->vendor == PCI_VENDOR_ID_INTEL) {
> > - unsigned short id;
> > - id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
> > + unsigned short id = pch->device &
> > INTEL_PCH_DEVICE_ID_MASK;
> > dev_priv->pch_id = id;
> >
> > if (id == INTEL_PCH_IBX_DEVICE_ID_TYPE) {
> > @@ -382,18 +379,15 @@ void intel_detect_pch(struct drm_device *dev)
> > DRM_DEBUG_KMS("Found LynxPoint LP PCH\n");
> > WARN_ON(!IS_HASWELL(dev));
> > WARN_ON(!IS_ULT(dev));
> > - } else {
> > - goto check_next;
> > - }
> > + } else
> > + continue;
> > +
> > pci_dev_put(pch);
> > break;
>
> Yep, looks better. I would also move the pci_dev_put out of the loop and
> remove the above continue. But it's fine for me either way.
Ah sorry, the continue is still needed. But for clarity I'd still move
the pci_dev_put out.
--Imre
>
> --Imre
>
> > }
> > -check_next:
> > - pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
> > - pci_dev_put(curr);
> > }
> > if (!pch)
> > - DRM_DEBUG_KMS("No PCH found?\n");
> > + DRM_DEBUG_KMS("No PCH found.\n");
> > }
> >
> >
>
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