From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031154Ab2I1T0k (ORCPT ); Fri, 28 Sep 2012 15:26:40 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:33712 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030329Ab2I1TCz (ORCPT ); Fri, 28 Sep 2012 15:02:55 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg KH , alan@lxorguk.ukuu.org.uk, Dave Airlie , Josh Boyer , Linus Torvalds Subject: [ 180/262] fbcon: fix race condition between console lock and cursor timer (v1.1) Date: Fri, 28 Sep 2012 11:51:49 -0700 Message-Id: <20120928183019.309331179@linuxfoundation.org> X-Mailer: git-send-email 1.7.10.1.362.g242cab3 In-Reply-To: <20120928182957.993484211@linuxfoundation.org> References: <20120928182957.993484211@linuxfoundation.org> User-Agent: quilt/0.60-2.1.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Greg KH 3.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dave Airlie commit d8636a2717bb3da2a7ce2154bf08de90bb8c87b0 upstream. 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. v1.1: add comment suggestion from Alan. Signed-off-by: Dave Airlie Acked-by: Alan Cox Tested-by: Josh Boyer Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/video/console/fbcon.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) --- a/drivers/video/console/fbcon.c +++ b/drivers/video/console/fbcon.c @@ -372,8 +372,15 @@ static void fb_flashcursor(struct work_s struct vc_data *vc = NULL; int c; int mode; + int ret; + + /* FIXME: we should sort out the unbind locking instead */ + /* instead we just fail to flash the cursor if we can't get + * the lock instead of blocking fbcon deinit */ + ret = console_trylock(); + if (ret == 0) + return; - console_lock(); if (ops && ops->currcon != -1) vc = vc_cons[ops->currcon].d;