Re: WARNING: CPU: 4 PID: 863 at include/drm/drm_crtc.h:1577 drm_helper_choose_encoder_dpms+0x88/0x90() - evildoer found and neutralized

From: Borislav Petkov
Date: Wed Sep 30 2015 - 13:36:28 EST

On Thu, Oct 01, 2015 at 01:00:44AM +0800, Jiang Liu wrote:
> Thanks Joerg, that makes sense. If some driver tries to binding to
> the IOMMU device, it will trigger the scenario as you described. For
> example, Xen backend driver will try to probe all PCI devices if
> enabled. I will do more investigation tomorrow.

Right, so this fixes the issue on my box, courtesy of Joerg. WE
basically don't disable the IRQ on MSI-enabled devices. The AMD IOMMU
uses a barebones PCI device but not a PCI driver, which would be an

diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index 09d3afc..29ec2eb 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -674,12 +674,15 @@ int pcibios_add_device(struct pci_dev *dev)

int pcibios_alloc_irq(struct pci_dev *dev)
+ if (pci_dev_msi_enabled(dev))
+ return 0;
return pcibios_enable_irq(dev);

void pcibios_free_irq(struct pci_dev *dev)
- if (pcibios_disable_irq)
+ if (!pci_dev_msi_enabled(dev) && pcibios_disable_irq)


ECO tip #101: Trim your mails when you reply.
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