From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 60FC6C742D1 for ; Fri, 12 Jul 2019 16:07:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4369E208E4 for ; Fri, 12 Jul 2019 16:07:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727068AbfGLQHs (ORCPT ); Fri, 12 Jul 2019 12:07:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53607 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726449AbfGLQHs (ORCPT ); Fri, 12 Jul 2019 12:07:48 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8386E30BC599; Fri, 12 Jul 2019 16:07:47 +0000 (UTC) Received: from dhcp-17-89.bos.redhat.com (dhcp-17-89.bos.redhat.com [10.18.17.89]) by smtp.corp.redhat.com (Postfix) with ESMTP id C7FFD5D756; Fri, 12 Jul 2019 16:07:46 +0000 (UTC) Subject: Re: [PATCH] drm: assure aux_dev is nonzero before using it To: =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= Cc: Jani Nikula , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, airlied@linux.ie, dkwon@redhat.com References: <20190523110905.22445-1-tcamuso@redhat.com> <87v9y0mept.fsf@intel.com> <5111581c-9d73-530d-d3ff-4f6950bf3f8c@redhat.com> <20190710135617.GE5942@intel.com> From: Tony Camuso Message-ID: <374b7e4e-40a2-f3c0-ae14-c533bd42243f@redhat.com> Date: Fri, 12 Jul 2019 12:07:46 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190710135617.GE5942@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Fri, 12 Jul 2019 16:07:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/10/19 9:56 AM, Ville Syrjälä wrote: > On Wed, Jul 10, 2019 at 09:47:11AM -0400, Tony Camuso wrote: >> On 5/24/19 4:36 AM, Jani Nikula wrote: >>> On Thu, 23 May 2019, tcamuso wrote: >>>> From Daniel Kwon >>>> >>>> The system was crashed due to invalid memory access while trying to access >>>> auxiliary device. >>>> >>>> crash> bt >>>> PID: 9863 TASK: ffff89d1bdf11040 CPU: 1 COMMAND: "ipmitool" >>>> #0 [ffff89cedd7f3868] machine_kexec at ffffffffb0663674 >>>> #1 [ffff89cedd7f38c8] __crash_kexec at ffffffffb071cf62 >>>> #2 [ffff89cedd7f3998] crash_kexec at ffffffffb071d050 >>>> #3 [ffff89cedd7f39b0] oops_end at ffffffffb0d6d758 >>>> #4 [ffff89cedd7f39d8] no_context at ffffffffb0d5bcde >>>> #5 [ffff89cedd7f3a28] __bad_area_nosemaphore at ffffffffb0d5bd75 >>>> #6 [ffff89cedd7f3a78] bad_area at ffffffffb0d5c085 >>>> #7 [ffff89cedd7f3aa0] __do_page_fault at ffffffffb0d7080c >>>> #8 [ffff89cedd7f3b10] do_page_fault at ffffffffb0d70905 >>>> #9 [ffff89cedd7f3b40] page_fault at ffffffffb0d6c758 >>>> [exception RIP: drm_dp_aux_dev_get_by_minor+0x3d] >>>> RIP: ffffffffc0a589bd RSP: ffff89cedd7f3bf0 RFLAGS: 00010246 >>>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff89cedd7f3fd8 >>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffc0a613e0 >>>> RBP: ffff89cedd7f3bf8 R8: ffff89f1bcbabbd0 R9: 0000000000000000 >>>> R10: ffff89f1be7a1cc0 R11: 0000000000000000 R12: 0000000000000000 >>>> R13: ffff89f1b32a2830 R14: ffff89d18fadfa00 R15: 0000000000000000 >>>> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 >>>> RIP: 00002b45f0d80d30 RSP: 00007ffc416066a0 RFLAGS: 00010246 >>>> RAX: 0000000000000002 RBX: 000056062e212d80 RCX: 00007ffc41606810 >>>> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 00007ffc41606ec0 >>>> RBP: 0000000000000000 R8: 000056062dfed229 R9: 00002b45f0cdf14d >>>> R10: 0000000000000002 R11: 0000000000000246 R12: 00007ffc41606ec0 >>>> R13: 00007ffc41606ed0 R14: 00007ffc41606ee0 R15: 0000000000000000 >>>> ORIG_RAX: 0000000000000002 CS: 0033 SS: 002b >>>> >>>> ---------------------------------------------------------------------------- >>>> >>>> It was trying to open '/dev/ipmi0', but as no entry in aux_dir, it returned >>>> NULL from 'idr_find()'. This drm_dp_aux_dev_get_by_minor() should have done a >>>> check on this, but had failed to do it. >>> >>> I think the better question is, *why* does the idr_find() return NULL? I >>> don't think it should, under any circumstances. I fear adding the check >>> here papers over some other problem, taking us further away from the >>> root cause. >>> >>> Also, can you reproduce this on a recent upstream kernel? The aux device >>> nodes were introduced in kernel v4.6. Whatever you reproduced on v3.10 >>> is pretty much irrelevant for upstream. >>> >>> >>> BR, >>> Jani. >> >> I have not been able to reproduce this problem. > > mknod /dev/foo c 255 > cat /dev/foo > > should do it. How do I determine ?