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 B9331CD5BC8 for ; Tue, 26 May 2026 12:51:02 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 236B210E17D; Tue, 26 May 2026 12:51:02 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="OsDazvTR"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id DD22310E17D for ; Tue, 26 May 2026 12:51:00 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id AB54F43937; Tue, 26 May 2026 12:51:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 667D11F00A3C; Tue, 26 May 2026 12:51:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779799860; bh=bteBqFYiwq3J6OuPkzqH8VWWC7H63MmZiDe/6GM4mCM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=OsDazvTRCqIezJKqXfh8OOKQB1X2daHZmZ45puukpTDNAAa4h2d68mcd1v7oAsw8I MZ4KKRpNxXIgxjh0jblCDvZ2+6jxwbyYf3V59oGWmdB4rY61G9qHgAJQpCJrV0vQJk h9CljaZISKs2pvdqgaSUjb90cD7nro4md0MGNbMtpmQT19WpWsGlJjeZOzUaSTu23K KJdoIDobh0UiM/xCW0LO1dCP5OMGzZle4e/Gr0q0YVtfL52Cf+puvNceX1sFgRabAC v54+J/ynVhiK/A+BVaqxSOE6Zq0M4LLd3og9dPz1Q+bwc9SmYM9Cj4a0iZ+2sKXx7P OZ8f2SNyYsLvg== Date: Tue, 26 May 2026 08:50:59 -0400 From: Sasha Levin To: Maarten Lankhorst 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> Subject: Re: [PATCH 6.18.y 0/5] drm/vkms: Backport generic vblank timer to fix ABBA deadlock Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <99f74d53-0060-4fed-b83e-955071883651@linux.intel.com> 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" 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. -- Thanks, Sasha