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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6F495C001B0 for ; Sun, 23 Jul 2023 14:32:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229745AbjGWOcR (ORCPT ); Sun, 23 Jul 2023 10:32:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229541AbjGWOcO (ORCPT ); Sun, 23 Jul 2023 10:32:14 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 30A2710E3 for ; Sun, 23 Jul 2023 07:32:14 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B90A360DC0 for ; Sun, 23 Jul 2023 14:32:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 934A5C433C8; Sun, 23 Jul 2023 14:32:11 +0000 (UTC) Date: Sun, 23 Jul 2023 10:32:10 -0400 From: Steven Rostedt To: Cc: regressions@lists.linux.dev, bagasdotme@gmail.com, alexander.deucher@amd.com, christian.koenig@amd.com, Xinhui.Pan@amd.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org Subject: Re: radeon.ko/i586: BUG: kernel NULL pointer dereference,address:00000004 Message-ID: <20230723103210.4b1b032e@rorschach.local.home> In-Reply-To: <230723205506.M0106064@vega.pgw.jp> References: <230722113014.M0204460@vega.pgw.jp> <230723205506.M0106064@vega.pgw.jp> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 23 Jul 2023 20:55:06 +0900 wrote: > So I tried to trap NULL and return: > > ================ patch-drm_vblank_cancel_pending_works-printk-NULL-ret.patch > diff -up ./drivers/gpu/drm/drm_vblank_work.c.pk2 ./drivers/gpu/drm/drm_vblank_work.c > --- ./drivers/gpu/drm/drm_vblank_work.c.pk2 2023-06-06 20:50:40.000000000 +0900 > +++ ./drivers/gpu/drm/drm_vblank_work.c 2023-07-23 14:29:56.383093673 +0900 > @@ -71,6 +71,10 @@ void drm_vblank_cancel_pending_works(str > { > struct drm_vblank_work *work, *next; > > + if (!vblank->dev) { > + printk(KERN_WARNING "%s: vblank->dev == NULL? returning\n", __func__); > + return; > + } > assert_spin_locked(&vblank->dev->event_lock); > > list_for_each_entry_safe(work, next, &vblank->pending_work, node) { > ================ > > This time, the printk trap does not happen!! and radeon.ko works. > (NULL check for vblank->worker is still fireing though) > > Now this is puzzling. > Is this a timing issue? It could very well be. And the ftrace patch could possibly not be the cause at all. But the thread that is created to do the work is causing the race window to be opened up, which is why you see it with the patch and don't without it. It may not be the problem, it may just tickle the timings enough to trigger the bug, and is causing you to go on a wild goose chase in the wrong direction. -- Steve > Is systemd-udevd doing something not favaorble to kernel? > Is drm vblank code running without enough initialization? > > Puzzling is, that purely useland activity > (logging in on tty1 before radeon.ko load) > is affecting kernel panic/no-panic.