Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762399AbXEKTkj (ORCPT ); Fri, 11 May 2007 15:40:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757925AbXEKTk3 (ORCPT ); Fri, 11 May 2007 15:40:29 -0400 Received: from smtp1.linux-foundation.org ([65.172.181.25]:43894 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755709AbXEKTk2 (ORCPT ); Fri, 11 May 2007 15:40:28 -0400 Date: Fri, 11 May 2007 12:39:59 -0700 From: Andrew Morton To: "Rafael J. Wysocki" Cc: Gautham R Shenoy , Linus Torvalds , LKML , Oleg Nesterov , Pavel Machek , "Eric W. Biederman" Subject: Re: [PATCH 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way Message-Id: <20070511123959.190adfaf.akpm@linux-foundation.org> In-Reply-To: <200705110036.26617.rjw@sisk.pl> References: <200705110035.32229.rjw@sisk.pl> <200705110036.26617.rjw@sisk.pl> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1718 Lines: 50 On Fri, 11 May 2007 00:36:25 +0200 "Rafael J. Wysocki" wrote: > The reading of PF_BORROWED_MM in is_user_space() without task_lock() is racy. > Fix it. > > Signed-off-by: Rafael J. Wysocki > Acked-by: Pavel Machek > --- > kernel/power/process.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > Index: linux-2.6/kernel/power/process.c > =================================================================== > --- linux-2.6.orig/kernel/power/process.c 2007-05-10 21:44:23.000000000 +0200 > +++ linux-2.6/kernel/power/process.c 2007-05-10 21:44:28.000000000 +0200 > @@ -8,6 +8,7 @@ > > #undef DEBUG > > +#include > #include > #include > #include > @@ -88,7 +89,12 @@ static void cancel_freezing(struct task_ > > static inline int is_user_space(struct task_struct *p) > { > - return p->mm && !(p->flags & PF_BORROWED_MM); > + int ret; > + > + task_lock(p); > + ret = p->mm && !(p->flags & PF_BORROWED_MM); > + task_unlock(p); > + return ret; > } The whole function is racy, isn't it? I mean, the condition which it is testing can go from true->false or false->true at any instant after this function returns its now-wrong value. iow, callers of this function need to to something to prevent the expression `p->mm && !(p->flags & PF_BORROWED_MM);' from changing value _anyway_. In which case the new locking is not needed? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/