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=-6.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 9DCC7C04AAF for ; Mon, 20 May 2019 08:22:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F6DB20815 for ; Mon, 20 May 2019 08:22:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="OWkQr9rR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730830AbfETIWZ (ORCPT ); Mon, 20 May 2019 04:22:25 -0400 Received: from mail-ed1-f67.google.com ([209.85.208.67]:43964 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725372AbfETIWZ (ORCPT ); Mon, 20 May 2019 04:22:25 -0400 Received: by mail-ed1-f67.google.com with SMTP id w33so22503798edb.10 for ; Mon, 20 May 2019 01:22:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=lJPBCrhSeCYaSH9F6UcUExEdsSLjSwQptqa3R/S5gDo=; b=OWkQr9rR7VJG+IgusEYX/ft1oKiDB1pCkBdMQY5rMfhIFUKTkY70KcXxSaEOeOyQCd 5K7bFk6hwIS7lVBMmwizciSEmiX15qitorn+tmcaf10m35kpUubkF16q/P+fziCAmsHh 9s5fYkl/JYG86U+9cnW7W2hnSycStsPXTTezk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=lJPBCrhSeCYaSH9F6UcUExEdsSLjSwQptqa3R/S5gDo=; b=aG8M38rbc7/xxo9Z4a0rTQz98eLt0x2dDoQzOwFXuEuQhkULd0ZeFNh6y2Zo2viZ7D IGWzQ2FfUtYGGT62p8FDn8yE+j/8qbyokDYdBo6Se8VxsB7Xy2BTDh3zgevAQAJnTWiL 24PmopUPlrNRMdNBaQoyZ/3m6UZQ4D2nrE9fWTefq1eBXVlj5RYW+l/VrMhrUa7PTk8c Rp1L9+iQuAG+1CBddEXzjeCqRbc34c1NjeXmrE4p9xrznAUz8XD1pT9VoqC9cSbAigId zZZLNZuXCoDO8QJmMh7wXqjRgIOLZrEVBQEk9j8GJdApCtpbpZLmvpvc1bQp/2AOXLcK c3aw== X-Gm-Message-State: APjAAAVDQV/BMSbEfoAoHU17iAqIQtgQxVS+B6I1nEmVLiEUZ+dggMBf WjCfHYXCL70MHhOetublDToeaySj0CU= X-Google-Smtp-Source: APXvYqyPl1hBLIWddTOYJ+pAidiSHSdpRExce6ICtNe8a3RnzrveD2FxJiDiiOT5ZYzgu/0s56EBjg== X-Received: by 2002:a50:9490:: with SMTP id s16mr74007144eda.260.1558340542484; Mon, 20 May 2019 01:22:22 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:569e:0:3106:d637:d723:e855]) by smtp.gmail.com with ESMTPSA id t25sm3021263ejx.8.2019.05.20.01.22.21 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 May 2019 01:22:21 -0700 (PDT) From: Daniel Vetter To: DRI Development Cc: Intel Graphics Development , LKML , Daniel Vetter Subject: [PATCH 00/33] fbcon notifier begone! Date: Mon, 20 May 2019 10:21:43 +0200 Message-Id: <20190520082216.26273-1-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, This patch series removes the fbcon notifier. It also contains the beginnings of trying to understand how locking in this area works. The super short summary of locking rules is that everything in fbcon needs to be protected by the monolithic console_lock, including the setup code. So not really an option to pull the kms modeset code out from underneath that, at least not without rewriting half the console layer. Or I'm not yet seeing clear enough. The other side is that fbdev userspace access vs. fbcon locking is totally broken. For context of this series I'm just going to quote the commit message that started this all: commit 6104c37094e729f3d4ce65797002112735d49cd1 Author: Daniel Vetter Date: Tue Aug 1 17:32:07 2017 +0200 fbcon: Make fbcon a built-time depency for fbdev There's a bunch of folks who're trying to make printk less contended and faster, but there's a problem: printk uses the console_lock, and the console lock has become the BKL for all things fbdev/fbcon, which in turn pulled in half the drm subsystem under that lock. That's awkward. There reasons for that is probably just a historical accident: - fbcon is a runtime option of fbdev, i.e. at runtime you can pick whether your fbdev driver instances are used as kernel consoles. Unfortunately this wasn't implemented with some module option, but through some module loading magic: As long as you don't load fbcon.ko, there's no fbdev console support, but loading it (in any order wrt fbdev drivers) will create console instances for all fbdev drivers. - This was implemented through a notifier chain. fbcon.ko enumerates all fbdev instances at load time and also registers itself as listener in the fbdev notifier. The fbdev core tries to register new fbdev instances with fbcon using the notifier. - On top of that the modifier chain is also used at runtime by the fbdev subsystem to e.g. control backlights for panels. - The problem is that the notifier puts a mutex locking context between fbdev and fbcon, which mixes up the locking contexts for both the runtime usage and the register time usage to notify fbcon. And at runtime fbcon (through the fbdev core) might call into the notifier from a printk critical section while console_lock is held. - This means console_lock must be an outer lock for the entire fbdev subsystem, which also means it must be acquired when registering a new framebuffer driver as the outermost lock since we might call into fbcon (through the notifier) which would result in a locking inversion if fbcon would acquire the console_lock from its notifier callback (which it needs to register the console). - console_lock can be held anywhere, since printk can be called anywhere, and through the above story, plus drm/kms being an fbdev driver, we pull in a shocking amount of locking hiercharchy underneath the console_lock. Which makes cleaning up printk really hard (not even splitting console_lock into an rwsem is all that useful due to this). There's various ways to address this, but the cleanest would be to make fbcon a compile-time option, where fbdev directly calls the fbcon register functions from register_framebuffer, or dummy static inline versions if fbcon is disabled. Maybe augmented with a runtime knob to disable fbcon, if that's needed (for debugging perhaps). But this could break some users who rely on the magic "loading fbcon.ko enables/disables fbdev framebuffers at runtime" thing, even if that's unlikely. Hence we must be careful: 1. Create a compile-time dependency between fbcon and fbdev in the least minimal way. This is what this patch does. 2. Wait at least 1 year to give possible users time to scream about how we broke their setup. Unlikely, since all distros make fbcon compile-in, and embedded platforms only compile stuff they know they need anyway. But still. 3. Convert the notifier to direct functions calls, with dummy static inlines if fbcon is disabled. We'll still need the fb notifier for the other uses (like backlights), but we can probably move it into the fb core (atm it must be built-into vmlinux). 4. Push console_lock down the call-chain, until it is down in console_register again. 5. Finally start to clean up and rework the printk/console locking. For context of this saga see commit 50e244cc793d511b86adea24972f3a7264cae114 Author: Alan Cox Date: Fri Jan 25 10:28:15 2013 +1000 fb: rework locking to fix lock ordering on takeover plus the pile of commits on top that tried to make this all work without terminally upsetting lockdep. We've uncovered all this when console_lock lockdep annotations where added in commit daee779718a319ff9f83e1ba3339334ac650bb22 Author: Daniel Vetter Date: Sat Sep 22 19:52:11 2012 +0200 console: implement lockdep support for console_lock On the patch itself: - Switch CONFIG_FRAMEBUFFER_CONSOLE to be a boolean, using the overall CONFIG_FB tristate to decided whether it should be a module or built-in. - At first I thought I could force the build depency with just a dummy symbol that fbcon.ko exports and fb.ko uses. But that leads to a module depency cycle (it works fine when built-in). Since this tight binding is the entire goal the simplest solution is to move all the fbcon modules (and there's a bunch of optinal source-files which are each modules of their own, for no good reason) into the overall fb.ko core module. That's a bit more than what I would have liked to do in this patch, but oh well. Signed-off-by: Daniel Vetter Cc: Alan Cox Cc: Sergey Senozhatsky Cc: Steven Rostedt Reviewed-by: Sean Paul Signed-off-by: Bartlomiej Zolnierkiewicz Comments, review and testing much appreciated, as always. Wrt long-term plans: I'm not sure where this will lead just yet, or whether it'll lead anywhere at all. But I think removing the notifier indirection is definitely a step into the right direction. Cheers, Daniel Daniel Vetter (33): dummycon: Sprinkle locking checks fbdev: locking check for fb_set_suspend vt: might_sleep() annotation for do_blank_screen vt: More locking checks fbdev/sa1100fb: Remove dead code fbdev/cyber2000: Remove struct display fbdev/aty128fb: Remove dead code fbcon: s/struct display/struct fbcon_display/ fbcon: Remove fbcon_has_exited fbcon: call fbcon_fb_(un)registered directly fbdev/sh_mobile: remove sh_mobile_lcdc_display_notify fbdev/omap: sysfs files can't disappear before the device is gone fbdev: sysfs files can't disappear before the device is gone staging/olpc: lock_fb_info can't fail fbdev/atyfb: lock_fb_info can't fail fbdev: lock_fb_info cannot fail fbcon: call fbcon_fb_bind directly fbdev: make unregister/unlink functions not fail fbdev: unify unlink_framebufer paths fbdev/sh_mob: Remove fb notifier callback fbdev: directly call fbcon_suspended/resumed fbcon: Call fbcon_mode_deleted/new_modelist directly fbdev: Call fbcon_get_requirement directly Revert "backlight/fbcon: Add FB_EVENT_CONBLANK" fbcon: directly call fbcon_fb_blanked fbmem: pull fbcon_fb_blanked out of fb_blank fbdev: remove FBINFO_MISC_USEREVENT around fb_blank fb: Flatten control flow in fb_set_var fbcon: replace FB_EVENT_MODE_CHANGE/_ALL with direct calls vgaswitcheroo: call fbcon_remap_all directly fbcon: Call con2fb_map functions directly fbcon: Document what I learned about fbcon locking staging/olpc_dcon: Add drm conversion to TODO drivers/gpu/vga/vga_switcheroo.c | 11 +- drivers/staging/olpc_dcon/TODO | 7 + drivers/staging/olpc_dcon/olpc_dcon.c | 6 +- drivers/tty/vt/vt.c | 18 + drivers/video/backlight/backlight.c | 2 +- drivers/video/backlight/lcd.c | 2 - drivers/video/console/dummycon.c | 6 + drivers/video/fbdev/aty/aty128fb.c | 64 --- drivers/video/fbdev/aty/atyfb_base.c | 3 +- drivers/video/fbdev/core/fbcmap.c | 6 +- drivers/video/fbdev/core/fbcon.c | 303 ++++++-------- drivers/video/fbdev/core/fbcon.h | 6 +- drivers/video/fbdev/core/fbmem.c | 374 ++++++------------ drivers/video/fbdev/core/fbsysfs.c | 20 +- drivers/video/fbdev/cyber2000fb.c | 1 - .../video/fbdev/omap2/omapfb/omapfb-sysfs.c | 21 +- drivers/video/fbdev/sa1100fb.c | 25 -- drivers/video/fbdev/sh_mobile_lcdcfb.c | 112 +----- drivers/video/fbdev/sh_mobile_lcdcfb.h | 5 - include/linux/console_struct.h | 5 +- include/linux/fb.h | 40 +- include/linux/fbcon.h | 30 ++ 22 files changed, 342 insertions(+), 725 deletions(-) -- 2.20.1