On Tue, Nov 08, 2016 at 05:29:57PM -0600, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: Hello Bjorn, Here are the answers on your questions inlined in the text. > Hi Serge, > > On Thu, Oct 06, 2016 at 12:34:15PM +0300, Serge Semin wrote: > > Hello linux folks, > > > > Sometime ago I discovered a kernel panic popping up when PCI subsystem was > > trying to enumerate PCI express bus with ASPM service enabled. Here it is: > > > > [ 5.089667] CPU 0 Unable to handle kernel paging request at virtual > > address 00000060, epc == 80317004, ra == 80316ac8 > > [ 5.120952] Oops[#1]: > > ... > > [ 5.528438] Call Trace: > > [ 5.535640] [<80317004>] pcie_aspm_init_link_state+0x6c0/0x814 > > [ 5.552843] [<80300c44>] pci_scan_slot+0x140/0x148 > > [ 5.566957] [<80301dcc>] pci_scan_child_bus+0x50/0x1b0 > > [ 5.582096] [<80301944>] pci_scan_bridge+0x25c/0x694 > > [ 5.596724] [<80301e78>] pci_scan_child_bus+0xfc/0x1b0 > > [ 5.611862] [<80301944>] pci_scan_bridge+0x25c/0x694 > > [ 5.626488] [<80301e78>] pci_scan_child_bus+0xfc/0x1b0 > > [ 5.641628] [<8030215c>] pci_scan_root_bus+0x64/0x124 > > [ 5.656528] [<804ca298>] pcibios_scanbus+0xa8/0x188 > > > > I more than sure you are familiar with the issue, since I've found the > > mailing discussion: "PCI: avoid NULL deref in alloc_pcie_link_state" > > https://patchwork.kernel.org/patch/2751651/ > > https://bugzilla.kernel.org/show_bug.cgi?id=60111 > > I'm trying to puzzle out a few things here. Maybe you can help me out? > > - Does this issue exist in current upstream kernels? Your dmesg shows a > v3.19-based kernel. c8fc9339409d ("PCI/ASPM: Use dev->has_secondary_link > to find downstream links"), which appeared in v4.2, fixes a problem very > similar to what you're reporting. > I saw that fix, but alas it hasn't fixed the issue. I've tested kernel 4.4.24 without my patch applied and the problem with ASPM-related kernel panic still exists (see the stack-trace above). > - When we dereference the NULL pointer, which device did we call > pcie_aspm_init_link_state() for? > My suggestion was that the problem arised in the framework of bus 2 enumeration. Since there was no root bus on my architecture, the pci_link_state structure was not created. So when the algorithm tried to enumerate the second bus, it needed actual pci_link_state structure of parental bus, which hadn't been created. That's how the NULL-dereference happened. > - https://bugzilla.kernel.org/attachment.cgi?id=240981 is the failing dmesg > log, and it shows "vgaarb: device added: PCI:0000:04:00.0". > > Your lspci output (https://bugzilla.kernel.org/attachment.cgi?id=241001) > shows 04:00.0 is a downstream port, but vga_arbiter_add_pci_device() only > prints that message for VGA class devices. > > https://bugzilla.kernel.org/attachment.cgi?id=240991, the successful > dmesg log, shows "vgaarb: device added: PCI:0000:06:00.0". That makes > more sense because 06:00.0 is class 0300, which is a VGA device. > > Bjorn I can't be sure about the reason of that strange enumeration. But I can assure you, that that bus confusion isn't the reason of the ASPM panicing. So I can just guess, that the misleading BDF can be caused by SMP (I've got a processor with two cores) and ASPM panic. VGA driver initialization may happen concurrently with PCI bus enumeration. Regards, -Sergey -- 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
