From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752258AbcKHXa6 (ORCPT ); Tue, 8 Nov 2016 18:30:58 -0500 Received: from mail.kernel.org ([198.145.29.136]:33688 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751674AbcKHXaz (ORCPT ); Tue, 8 Nov 2016 18:30:55 -0500 Date: Tue, 8 Nov 2016 17:29:57 -0600 From: Bjorn Helgaas To: Serge Semin Cc: bhelgaas@google.com, shawn.lin@rock-chips.com, luto@kernel.org, Sergey.Semin@t-platforms.ru, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] PCI: Fix kernel panic of root-port-less PCIe enum due to ASPM Message-ID: <20161108232957.GH14322@bhelgaas-glaptop.roam.corp.google.com> References: <1475746455-20665-1-git-send-email-fancer.lancer@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1475746455-20665-1-git-send-email-fancer.lancer@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. - When we dereference the NULL pointer, which device did we call pcie_aspm_init_link_state() for? - 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