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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7EE9BCD5BC8 for ; Tue, 26 May 2026 12:59:14 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D9E7010E4B4; Tue, 26 May 2026 12:59:13 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="F78mpPok"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.13]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0D26110E49D for ; Tue, 26 May 2026 12:59:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1779800352; x=1811336352; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=dx1QHl+ZguvyLwxXmsMyaqqMGmA9+UMAzdhIOUGhOPc=; b=F78mpPokKfaR4hw4KCBPcWmrqoLXniUTR+B9buP0xROQVhMXWpDsDqmz SIM9Df0LBiqB7p7GGpkoYeLrufUp/3d5GSr4KqkSh9I4L8mvdrNgwDTcB wu1OP5ZoTZ7Rllfrc+sPku3/LjOETqWjaG2VCwTZJosA4De6ko865GsRr eaIp5ohtDuEwZ6NsRJF71kCeZTWitvfE2f59K328LmG2zrrY/9t0/RHDk tMe+0BhZCpQa0mmEd+RBCkgPSXTGVixJu7MtueNjvmTM0mYZafZADE3UO ZLnsiijcq8UjWIjqAa0++2PJBpWlRTjhb+gwkawzJjOVCorafJa8dAsWl Q==; X-CSE-ConnectionGUID: SC50nMVuTWONdZDSC9Np9Q== X-CSE-MsgGUID: Ry833+rDSVq6+Z9LDyENnA== X-IronPort-AV: E=McAfee;i="6800,10657,11797"; a="91718384" X-IronPort-AV: E=Sophos;i="6.24,169,1774335600"; d="scan'208";a="91718384" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 May 2026 05:59:12 -0700 X-CSE-ConnectionGUID: a7ruXhaqQZq5EUNAguQlYg== X-CSE-MsgGUID: ftIw7pVfSfSH9tlggCYiJw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,169,1774335600"; d="scan'208";a="241993485" Received: from conormcd-mobl2.ger.corp.intel.com (HELO [10.245.244.113]) ([10.245.244.113]) by orviesa009-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 May 2026 05:59:09 -0700 Message-ID: <34bfe775-32bc-4ff9-bb41-1707956dbaeb@linux.intel.com> Date: Tue, 26 May 2026 14:59:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.18.y 0/5] drm/vkms: Backport generic vblank timer to fix ABBA deadlock To: Sasha Levin Cc: w15303746062 , stable@vger.kernel.org, gregkh@linuxfoundation.org, tzimmermann@suse.de, mripard@kernel.org, louis.chauvet@bootlin.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Mingyu Wang <25181214217@stu.xidian.edu.cn> References: <9c4a68c4-43a3-4a9b-a131-9570174c8df3@linux.intel.com> <20260525131610.608273-1-w15303746062@163.com> <20260525231000.agent5-0001@kernel.org> <51ff85d2.9c25.19e642e591c.Coremail.w15303746062@163.com> <99f74d53-0060-4fed-b83e-955071883651@linux.intel.com> Content-Language: en-US From: Maarten Lankhorst In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Den 2026-05-26 kl. 14:50, skrev Sasha Levin: > On Tue, May 26, 2026 at 02:48:55PM +0200, Maarten Lankhorst wrote: >> Hello, >> >> Den 2026-05-26 kl. 14:06, skrev w15303746062: >>> >>> Hi Sasha, >>> >>>> Looking at the five commits: >>>> >>>>  - 1/5 (74afeb812850) is the one that actually fixes the ABBA >>>>    deadlock you observed under Syzkaller; it adds the generic vblank >>>>    timer that replaces the open-coded vkms hrtimer path. >>>> >>>>  - 2/5 (d54dbb5963bd) adds new CRTC helpers for "simple use cases". >>>>    No Fixes:/Cc:stable, no described bug. >>>> >>>>  - 3/5 (02e2681ffe1a) is a refactor that converts vkms to the new >>>>    helpers. No Fixes:/Cc:stable, no described bug. >>>> >>>>  - 4/5 (79ae8510b5b8) is a v7.1-rc1 timeout bump that depends on 1/5. >>>>    It is not yet in any released stable, so applying it to 6.18.y >>>>    would put it on an LTS before any LTS contains it. >>>> >>>>  - 5/5 (3946d3ba9934) is a doc fix for 1/5. >>>> >>>> Per stable-kernel-rules, what I need to queue is the minimum set that >>>> fixes the bug. Could you explain, per patch, why 2/5..5/5 are required >>>> to make 1/5 work / are required to actually fix the deadlock? If only >>>> 1/5 is needed, please resend just that one with your Signed-off-by >>>> added (the carried patches today only have Thomas's S-o-b, which >>>> breaks the chain of custody on a stable submission). >>> >>> Thanks for the quick review and for pointing out the missing Signed-off-by. I apologize for that omission; it was my mistake during the cherry-pick process. >>> >>> Regarding the dependency chain, I would like to clarify why commit 1/5 alone cannot fix the issue: >>> >>> Commits 1/5 and 2/5 introduce the new generic vblank timer infrastructure to the DRM core but do *not* touch the vkms driver at all. >>> Commit 3/5 (02e2681ffe1a) is the actual fix that modifies `drivers/gpu/drm/vkms/vkms_crtc.c`. It removes the buggy open-coded hrtimer that causes the ABBA deadlock and switches vkms to use the new infrastructure introduced in 1/5 and 2/5. >>> >>> Therefore, 1/5, 2/5, and 3/5 form an indivisible set. Applying only 1/5 would leave the deadlock in vkms completely unpatched. >>> >>> As for 4/5 and 5/5 (the timeout bump and doc fix), Maarten Lankhorst (DRM maintainer) explicitly recommended pulling in this exact 5-commit list as the proper upstream fix for this specific vkms issue (see the mailing list link in this thread). >>> >>> However, if you feel 4/5 and 5/5 introduce unnecessary risk for the 6.18.y stable tree, I can absolutely drop them and only submit 1/5, 2/5, and 3/5. >>> >>> I am preparing a v2 patch series now with my Signed-off-by added to the chain of custody. Could you let me know if you prefer the full 5-patch series as recommended by DRM maintainers, or just the minimal 3-patch series? >>> >>> Best regards, >>> Mingyu >> >> 5/5 might strictly speaking not be needed as it's a documentation fix and I have no idea of the policy about those. >> >> The reporter made a bug report of an ABBA deadlock that was fixed in upstream by the first 4 patches, perhaps it's good to those attach here to this discussion. > > I have no objection to taking all 5 if you're okay with it. > Mingyu made an effort to reproduce, check if commits fixed it and then checked if other drivers needed the same bug fixed. I'm ok with the series. Kind regards, ~Maarten Lankhorst