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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 4F88CC04AAF for ; Mon, 20 May 2019 08:23:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 250862081C for ; Mon, 20 May 2019 08:23:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="Rbh03cPz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731538AbfETIXO (ORCPT ); Mon, 20 May 2019 04:23:14 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:41955 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731482AbfETIXB (ORCPT ); Mon, 20 May 2019 04:23:01 -0400 Received: by mail-ed1-f65.google.com with SMTP id m4so22532306edd.8 for ; Mon, 20 May 2019 01:23:00 -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:in-reply-to:references :mime-version:content-transfer-encoding; bh=FCOGJKruV68PCMlFcu0Jcdh8P9H2/Ftv0Ji3KZWmbUo=; b=Rbh03cPzhJBRqu9N582ybR/hmSNxX1iWpRzgNhumzuQbtDBL/jZRwtE6ZiEMqds9e5 nCEi/0ReTps2K5chpBg2DyfeG8uZ0uMJ48T7NmIfs/PZqn8j6RZVAiv4FMoOYEF4THte f9YBRVbl9RZXkjWKtYSH8orRr9dQVQY+ptY/M= 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=FCOGJKruV68PCMlFcu0Jcdh8P9H2/Ftv0Ji3KZWmbUo=; b=fbjGlykc8XMYV3bYDbT7WKkWNXbEsIGgTanPc5bRtVDF/2H6FkMswPRic0DjnXuKaS 44qIfDgZpBtdUVforqu9+91rYtnxcnwIHCuGkXA6H+nn2lPYen7qHoV9rSSv6Ubso9xj zXnWfM+hTjOgF71znKeJdXE0Gdd7DIynyoxUMRKtivF27Ng3+7Rir64IK0kO/VDC28YN wqeZThvlY3mwwTNCtrw2HqYZsDBJ9gn7r/Oa1Zv+chLMVUUxfUK8eqSkIUC7E4FA9yqp 0e5sNNq45xBDbhWTCwm5s64MTlBQpq3+j3SjkP2VwGOv4sTDwgN5qGnvCfpFx83Mw8HT IdhA== X-Gm-Message-State: APjAAAXbzcjfwFxKZPMXfUjoitYeHJ3SoB2212SRlGBBXy1R8eDeGQpk cEGUYJsCHZvlonJA42ofcALYlw== X-Google-Smtp-Source: APXvYqz+JhrLTRZhNTc3DaIv8DkUxRltlxdyj4OAkPrhoscMsBVYEJlPpazmYVAIf3UpLblLmQV4AQ== X-Received: by 2002:a17:906:7d50:: with SMTP id l16mr57720102ejp.84.1558340579630; Mon, 20 May 2019 01:22:59 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:569e:0:3106:d637:d723:e855]) by smtp.gmail.com with ESMTPSA id t25sm3021263ejx.8.2019.05.20.01.22.58 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 May 2019 01:22:59 -0700 (PDT) From: Daniel Vetter To: DRI Development Cc: Intel Graphics Development , LKML , Daniel Vetter , Daniel Vetter , Bartlomiej Zolnierkiewicz , Hans de Goede , Yisheng Xie Subject: [PATCH 32/33] fbcon: Document what I learned about fbcon locking Date: Mon, 20 May 2019 10:22:15 +0200 Message-Id: <20190520082216.26273-33-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190520082216.26273-1-daniel.vetter@ffwll.ch> References: <20190520082216.26273-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It's not pretty. Signed-off-by: Daniel Vetter Cc: Daniel Vetter Cc: Bartlomiej Zolnierkiewicz Cc: Hans de Goede Cc: Yisheng Xie --- drivers/video/fbdev/core/fbcon.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index b40b56702c61..cbbcf7a795f2 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -87,6 +87,25 @@ # define DPRINTK(fmt, args...) #endif +/* + * FIXME: Locking + * + * - fbcon state itself is protected by the console_lock, and the code does a + * pretty good job at making sure that lock is held everywhere it's needed. + * + * - access to the registered_fb array is entirely unprotected. This should use + * proper object lifetime handling, i.e. get/put_fb_info. This also means + * switching from indices to proper pointers for fb_info everywhere. + * + * - fbcon doesn't bother with fb_lock/unlock at all. This is buggy, since it + * means concurrent access to the same fbdev from both fbcon and userspace + * will blow up. To fix this all fbcon calls from fbmem.c need to be moved out + * of fb_lock/unlock protected sections, since otherwise we'll recurse and + * deadlock eventually. Aside: Due to these deadlock issues the fbdev code in + * fbmem.c cannot use locking asserts, and there's lots of callers which get + * the rules wrong, e.g. fbsysfs.c entirely missed fb_lock/unlock calls too. + */ + enum { FBCON_LOGO_CANSHOW = -1, /* the logo can be shown */ FBCON_LOGO_DRAW = -2, /* draw the logo to a console */ -- 2.20.1