On Tue, Jun 25, 2013 at 5:23 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > On Mon, Jun 24, 2013 at 07:38:45PM -0600, Bjorn Helgaas wrote: >> [+cc Michael, Alex, Isaku] >> >> On Wed, Jun 19, 2013 at 12:56 PM, Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: >> > PCIe switch upstream port can be connected directly to the PCIe root bus >> > in QEMU; ASPM does not expect this topology and dereferences NULL pointer >> > when initializing. >> > >> > I have not confirmed this can happen on real hardware, but it is presented >> > as a feature in QEMU, so there is no reason to panic if we can recover. >> >> This doesn't seem like a valid hardware topology to me. If this *can* >> occur on real hardware, we should fix it in Linux. If not, maybe QEMU >> should be changed to disallow it. > > I don't think it's a spec compliant topology either. > > Anything connected to an RC is either an integrated endpoint > or a root port. > There's no way to have an upstream port that is also > an integrated endpoint or a root port - these are distinct > device types. > > So I don't think Linux needs to support it. > > Having said that, there's all kind of broken hardware > out there - crashing is not a friendly way to tell users > that their hardware is not spec compliant. > Maybe linux can print a friendly warning and ignore > this port? Indeed, that would be nicer. I booted Win7 on the same config, and it came up fine. It did complain that it couldn't start the PCI-to-PCI bridge driver on 00:03.0, the upstream port. I'd like it if Linux could similarly tolerate that. But since this is a relatively low-priority issue, I'm going to hold out for a more straightforward solution. Checking for a null "pdev->bus->parent->self" pointer is not very obvious. I think we can probably come up with a more direct check that reads better and possibly even detects the issue at the upstream port, not the downstream port. I opened a bugzilla for this issue: https://bugzilla.kernel.org/show_bug.cgi?id=60111 Radim, can you please attach a complete dmesg log showing the oops, i.e., console output with "ignore_loglevel" and lspci -vv output (have to use your patch so it boots, I guess)? I tried to reproduce it and I know the problem is there, but I haven't quite found the right recipe yet. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
