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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 AD828C433DB for ; Tue, 12 Jan 2021 15:58:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61657207D0 for ; Tue, 12 Jan 2021 15:58:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405367AbhALP61 (ORCPT ); Tue, 12 Jan 2021 10:58:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56076 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732573AbhALP60 (ORCPT ); Tue, 12 Jan 2021 10:58:26 -0500 Received: from mail-ot1-x335.google.com (mail-ot1-x335.google.com [IPv6:2607:f8b0:4864:20::335]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE850C061794 for ; Tue, 12 Jan 2021 07:57:45 -0800 (PST) Received: by mail-ot1-x335.google.com with SMTP id b24so2722857otj.0 for ; Tue, 12 Jan 2021 07:57:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ipPU2vUc+BFfUi92jCI9tLYRCUYmdD6X+lgC1SjK0wc=; b=N/kJEm00glSMDkxyusQwQrXuK/TuEczkrU13epKkLv4ZujV7CmBMz7zExMyAmD/c8V fn4UuIte+aoF6LalD6gqyintU4Sx+9Y/524JjdnFYzLFIXD1OIRHQoZuytPVhhhbEBOD cC7OkVGttZF6yeiEnyVnJ+Dirk1yKpLg3XsWM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ipPU2vUc+BFfUi92jCI9tLYRCUYmdD6X+lgC1SjK0wc=; b=L/b2LecvUTVaGCh0idgzGJrEpDnTs5Kduk3SjTWRn06DrXg1BGzC55biAfB5kg699q FpH4Buza7AQPnpJT4xed/kHPU56dp6nfifSBrx9xdl/3lMIBM1asAg+ICH0R0WoFhVMM NG3aILNps2L4Fund24SS5fkWeAFPaicrVpXj23XDb0d8wB8rZsrBqEPWpOrdBa7PXRgX nf3MS7Pf/irYuipKoMOAAN2Oqzn6qxf04Nni3h+D1FMLRP6WfcygPXwoHj2zKjlzb9vW 5IHlwMQurrLe7IXMXi2R2G3kmcCz9R8oyIvZRZboVyJHF5DI4gZhke355hSAP/86K41I RkJw== X-Gm-Message-State: AOAM532/VmMXer5DJkkHns5WZQQwauzbsknwZ9oDaT9DtxSX+qq+DVOf ZVxEf9fZsCWMq/KS3WOkrMkzwO21+zyWOL5nftXycg== X-Google-Smtp-Source: ABdhPJzXSshJQKExSJsT5ioLk9EsBQSNfGxfM3kxQUxKh+G7AoddxywtMTAUCL44UVcbxALZuyaFQc/OpgMmBHp1mPc= X-Received: by 2002:a05:6830:1bef:: with SMTP id k15mr8948otb.303.1610467065202; Tue, 12 Jan 2021 07:57:45 -0800 (PST) MIME-Version: 1.0 References: <20200916205434.GA10389@duo.ucw.cz> <87czyf5jjp.fsf@vps.thesusis.net> In-Reply-To: From: Daniel Vetter Date: Tue, 12 Jan 2021 16:57:34 +0100 Message-ID: Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch) To: Linus Torvalds Cc: Phillip Susi , Pavel Machek , Randy Dunlap , LKML , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , dri-devel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 9, 2021 at 12:11 AM Linus Torvalds wrote: > > On Fri, Jan 8, 2021 at 11:13 AM Phillip Susi wrote: > > > > > Could we pause this madness? Scrollback is still useful. I needed it > > > today... it was too small, so command results I was looking for > > > already scrolled away, but... life will be really painful with 0 > > > scrollback. > > > > > You'll need it, too... as soon as you get oops and will want to see > > > errors just prior to that oops. > > > > > If it means I get to maintain it... I'm not happy about it but that's > > > better than no scrollback. > > > > Amen! What self respecting admin installs a gui on servers? What do we > > have to do to get this back in? What was so buggy with this code that > > it needed to be removed? Why was it such a burden to just leave it be? > > It really was buggy, with security implications. And we have no maintainers. > > So the scroll-back code can't come back until we have a maintainer and > a cleaner and simpler implementation. > > And no, maintaining it really doesn't mean "just get it back to the > old broken state". > > So far I haven't actually seen any patches, which means that it's not > coming back. > > The good news? If you have an actual text VGA console, that should > still work just fine. Also on anything that is remotely modern (i.e. runs a drm kernel modesetting driver undearneath the fbdev/fbcon stack) there's a pile more issues on top of just the scrollback/fbcon code being a mess. Specifically the locking is somewhere between yolo and outright deadlocks. This holds even more so if the use case here is "I want scrollback for an oops". There's rough sketches for how it could be solved, but it's all very tricky work. Also, we need testcases for this, both in-kernel unit-test style stuff and uapi testcases. Especially the full interaction on a modern stack between /dev/fb/0, /dev/drm/card0, vt ioctls and the console is a pure nightmare. Altogether this is a few years of full time hacking to get this back into shape, and until that's happening and clearly getting somewhere the only reasonable thing to do is to delete features in response to syzkaller crashes. Also adding dri-devel since defacto that's the only place where display people hang out nowadays. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch 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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 B33E3C433E0 for ; Tue, 12 Jan 2021 15:57:48 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id D298920782 for ; Tue, 12 Jan 2021 15:57:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D298920782 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 03C276E247; Tue, 12 Jan 2021 15:57:47 +0000 (UTC) Received: from mail-ot1-x32f.google.com (mail-ot1-x32f.google.com [IPv6:2607:f8b0:4864:20::32f]) by gabe.freedesktop.org (Postfix) with ESMTPS id E9D136E247 for ; Tue, 12 Jan 2021 15:57:45 +0000 (UTC) Received: by mail-ot1-x32f.google.com with SMTP id x13so2683073oto.8 for ; Tue, 12 Jan 2021 07:57:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ipPU2vUc+BFfUi92jCI9tLYRCUYmdD6X+lgC1SjK0wc=; b=N/kJEm00glSMDkxyusQwQrXuK/TuEczkrU13epKkLv4ZujV7CmBMz7zExMyAmD/c8V fn4UuIte+aoF6LalD6gqyintU4Sx+9Y/524JjdnFYzLFIXD1OIRHQoZuytPVhhhbEBOD cC7OkVGttZF6yeiEnyVnJ+Dirk1yKpLg3XsWM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ipPU2vUc+BFfUi92jCI9tLYRCUYmdD6X+lgC1SjK0wc=; b=DxXNluLbijhiO5FqZTevYxutfGm3d5g+RBnkvVNqQGkjSO1sfVH/8boJUwBuHTk81v OHGWIexAefOrsCAEn9y++oHdBEboIgAlK9p5ljZwwjMo8R5u+bx8zrP5ZsH82OzyGSWD uJ5/pyI78QBv/i7KUFpXqapOCr50s6Qz9BRAnedyCI9R8VVuLlrLtfOEn0bAFsj9UFPY SXXHrCUrEq7eBeJuirJB3eiWZYNpGlZDjxIfEW6BBwbVWzVFr28eZMmL1jzjqK9p1VCH L0nPoHJ7/A+BfZesbMpeIJKFBlfL1sn8UfG/NhoB7x8Cj2jChRSAmvXqB+i7GtVQdwhS Zz6A== X-Gm-Message-State: AOAM531PQzlBiPtoceXJ6AGVpyZtAdBUXbMuh+ZanDoRN4IxjFPtiw6E lLr7vjem1Zcl/p/mo+oqRKNL9xTXLavgyvuAKgxWOw== X-Google-Smtp-Source: ABdhPJzXSshJQKExSJsT5ioLk9EsBQSNfGxfM3kxQUxKh+G7AoddxywtMTAUCL44UVcbxALZuyaFQc/OpgMmBHp1mPc= X-Received: by 2002:a05:6830:1bef:: with SMTP id k15mr8948otb.303.1610467065202; Tue, 12 Jan 2021 07:57:45 -0800 (PST) MIME-Version: 1.0 References: <20200916205434.GA10389@duo.ucw.cz> <87czyf5jjp.fsf@vps.thesusis.net> In-Reply-To: From: Daniel Vetter Date: Tue, 12 Jan 2021 16:57:34 +0100 Message-ID: Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch) To: Linus Torvalds 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: , Cc: Phillip Susi , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , Randy Dunlap , LKML , dri-devel , Pavel Machek Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Sat, Jan 9, 2021 at 12:11 AM Linus Torvalds wrote: > > On Fri, Jan 8, 2021 at 11:13 AM Phillip Susi wrote: > > > > > Could we pause this madness? Scrollback is still useful. I needed it > > > today... it was too small, so command results I was looking for > > > already scrolled away, but... life will be really painful with 0 > > > scrollback. > > > > > You'll need it, too... as soon as you get oops and will want to see > > > errors just prior to that oops. > > > > > If it means I get to maintain it... I'm not happy about it but that's > > > better than no scrollback. > > > > Amen! What self respecting admin installs a gui on servers? What do we > > have to do to get this back in? What was so buggy with this code that > > it needed to be removed? Why was it such a burden to just leave it be? > > It really was buggy, with security implications. And we have no maintainers. > > So the scroll-back code can't come back until we have a maintainer and > a cleaner and simpler implementation. > > And no, maintaining it really doesn't mean "just get it back to the > old broken state". > > So far I haven't actually seen any patches, which means that it's not > coming back. > > The good news? If you have an actual text VGA console, that should > still work just fine. Also on anything that is remotely modern (i.e. runs a drm kernel modesetting driver undearneath the fbdev/fbcon stack) there's a pile more issues on top of just the scrollback/fbcon code being a mess. Specifically the locking is somewhere between yolo and outright deadlocks. This holds even more so if the use case here is "I want scrollback for an oops". There's rough sketches for how it could be solved, but it's all very tricky work. Also, we need testcases for this, both in-kernel unit-test style stuff and uapi testcases. Especially the full interaction on a modern stack between /dev/fb/0, /dev/drm/card0, vt ioctls and the console is a pure nightmare. Altogether this is a few years of full time hacking to get this back into shape, and until that's happening and clearly getting somewhere the only reasonable thing to do is to delete features in response to syzkaller crashes. Also adding dri-devel since defacto that's the only place where display people hang out nowadays. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel