From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422857AbXCOOlh (ORCPT ); Thu, 15 Mar 2007 10:41:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422861AbXCOOlh (ORCPT ); Thu, 15 Mar 2007 10:41:37 -0400 Received: from ipn26-148.piekary.net ([83.238.26.148]:51408 "EHLO ipn26-148.piekary.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422857AbXCOOlg (ORCPT ); Thu, 15 Mar 2007 10:41:36 -0400 X-Greylist: delayed 1871 seconds by postgrey-1.27 at vger.kernel.org; Thu, 15 Mar 2007 10:41:36 EDT Date: Thu, 15 Mar 2007 15:10:23 +0100 From: Michal Januszewski To: linux-kernel@vger.kernel.org Subject: [PATCH] vt: fix a potential race in the VT_WAITACTIVE handler Message-ID: <20070315141023.GA9757@spock.one.pl> Reply-To: spock@gentoo.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Disposition: inline X-PGP-Key: http://dev.gentoo.org/~spock/spock.gpg User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On a multiprocessor machine the VT_WAITACTIVE ioctl call may return 0 if fg_console has already been updated in redraw_screen(), but the console switch itself hasn't been completed. Fix this by checking fg_console in vt_waitactive() with the console sem held. Signed-off-by: Michal Januszewski --- diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c index 3a5d301..00b5b34 100644 --- a/drivers/char/vt_ioctl.c +++ b/drivers/char/vt_ioctl.c @@ -1041,8 +1041,12 @@ int vt_waitactive(int vt) for (;;) { set_current_state(TASK_INTERRUPTIBLE); retval = 0; - if (vt == fg_console) + acquire_console_sem(); + if (vt == fg_console) { + release_console_sem(); break; + } + release_console_sem(); retval = -EINTR; if (signal_pending(current)) break;