From patchwork Tue Aug 21 06:40:07 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Airlie X-Patchwork-Id: 1352511 Return-Path: X-Original-To: patchwork-linux-fbdev@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id C08CCDFB34 for ; Tue, 21 Aug 2012 06:40:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751582Ab2HUGkl (ORCPT ); Tue, 21 Aug 2012 02:40:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18278 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751036Ab2HUGkl (ORCPT ); Tue, 21 Aug 2012 02:40:41 -0400 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q7L6eJ4K014799 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Tue, 21 Aug 2012 02:40:19 -0400 Received: from prime.bne.redhat.com (dhcp-41-76.bne.redhat.com [10.64.41.76]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id q7L6eFfB029177; Tue, 21 Aug 2012 02:40:16 -0400 From: Dave Airlie To: linux-fbdev@vger.kernel.org Cc: dri-devel@lists.sf.net, linux-kernel@vger.kernel.org, Linus , Alan Cox , Randy Dunlap , Josh Boyer , Dave Airlie Subject: [PATCH] fbcon: fix race condition between console lock and cursor timer Date: Tue, 21 Aug 2012 16:40:07 +1000 Message-Id: <1345531207-24926-1-git-send-email-airlied@redhat.com> X-Scanned-By: MIMEDefang 2.67 on 10.5.11.11 Sender: linux-fbdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org So we've had a fair few reports of fbcon handover breakage between efi/vesafb and i915 surface recently, so I dedicated a couple of days to finding the problem. Essentially the last thing we saw was the conflicting framebuffer message and that was all. So after much tracing with direct netconsole writes (printks under console_lock not so useful), I think I found the race. Thread A (driver load) Thread B (timer thread) unbind_con_driver -> | bind_con_driver -> | vc->vc_sw->con_deinit -> | fbcon_deinit -> | console_lock() | | | | fbcon_flashcursor timer fires | console_lock() <- blocked for A | | fbcon_del_cursor_timer -> del_timer_sync (BOOM) Of course because all of this is under the console lock, we never see anything, also since we also just unbound the active console guess what we never see anything. Hopefully this fixes the problem for anyone seeing vesafb->kms driver handoff. Signed-off-by: David Airlie --- drivers/video/console/fbcon.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c index 2e471c2..f8a79fc 100644 --- a/drivers/video/console/fbcon.c +++ b/drivers/video/console/fbcon.c @@ -372,8 +372,12 @@ static void fb_flashcursor(struct work_struct *work) struct vc_data *vc = NULL; int c; int mode; + int ret; + + ret = console_trylock(); + if (ret == 0) + return; - console_lock(); if (ops && ops->currcon != -1) vc = vc_cons[ops->currcon].d;