From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D4FFF222597; Tue, 26 May 2026 12:49:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779799743; cv=none; b=lMbU8AzokLoRavqm/K8USRJ+1zn2jp2FAca0dsFBHs+cRGNZ4xOoMEVyHXH/l5L7JvnNOhwvUlq2ee1KZXKmQxoEKpWY5gfg8zi15LRaDgIHGjAt+35c0oJYAxaDT0F/I4lmWsK/t6YqW3PHZ8L4yAObCgEcHdo3SW4XeC7wk+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779799743; c=relaxed/simple; bh=VCpyIz4nKjkWSGeEJFlo4VCbFIDHAjaOkR/pMAOHCSg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FOO8j1u+sb4SLLP0jL/E0jifoMMT3Ari/0a7atzjharqy9f+dQrcDqUXikVIRvy+c2LDoTTfpMspQ9vaxNmQVFrlJswSZmFLq261Tan7yEDic6oozyqHYfdEGBkdrfdIMT0o724+hWTxX+YO2yXSGJTKN9iCpHvDkaRf/p39ukY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=N2PwWHOu; arc=none smtp.client-ip=198.175.65.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="N2PwWHOu" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1779799741; x=1811335741; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=VCpyIz4nKjkWSGeEJFlo4VCbFIDHAjaOkR/pMAOHCSg=; b=N2PwWHOulGm/YxiyuzmYK1GNtF3UGhU7DsXXq6WDQPsg3JJWsCK9nKEW nTOwlDTJrycO6mGJIEVJQSBTzs2NQQTVnIiY1D8Wh5vjQ6dBEJsClANwu LQs2NBwDO6mNeT1tAzK7tdfwOIG/Am6Xjh5V0BWsMKSu3vE0mZ2Za8UTS fLjt5B2kOuj4rBvNIJA+SXY/v4A5PStjK1UnMTEqBbFz6fO83r7sgIRNQ dMjsRT5Ix/sPlzOTCgCzHYDn9NtUM5WQsKZLcvDXOlAGgb1hJtjfFydwr JpNSpKvx7v1CJjFOUSYehX1XZSjQgSW6mGpvLjEb8ozcs+o1Fpxug+zWU w==; X-CSE-ConnectionGUID: YWPhufCWT1mdtO6XiWMJhg== X-CSE-MsgGUID: ZaUAPD4vTeSGvSyb8st1Sg== X-IronPort-AV: E=McAfee;i="6800,10657,11797"; a="98034368" X-IronPort-AV: E=Sophos;i="6.24,169,1774335600"; d="scan'208";a="98034368" Received: from fmviesa007.fm.intel.com ([10.60.135.147]) by orvoesa102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 May 2026 05:49:00 -0700 X-CSE-ConnectionGUID: +1DEV9KRReCtulYpbdvNEg== X-CSE-MsgGUID: HVqWz8g/SaKDY3+PSwr0uw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,169,1774335600"; d="scan'208";a="238892788" Received: from conormcd-mobl2.ger.corp.intel.com (HELO [10.245.244.113]) ([10.245.244.113]) by fmviesa007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 May 2026 05:48:57 -0700 Message-ID: <99f74d53-0060-4fed-b83e-955071883651@linux.intel.com> Date: Tue, 26 May 2026 14:48:55 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: w15303746062 , Sasha Levin Cc: 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> Content-Language: en-US From: Maarten Lankhorst In-Reply-To: <51ff85d2.9c25.19e642e591c.Coremail.w15303746062@163.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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. Kind regards, ~Maarten Lankhorst