Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755759Ab2EETcH (ORCPT ); Sat, 5 May 2012 15:32:07 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:53689 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754933Ab2EETcF (ORCPT ); Sat, 5 May 2012 15:32:05 -0400 Date: Sat, 5 May 2012 23:32:01 +0400 From: Cyrill Gorcunov To: Vasiliy Kulikov Cc: Sasha Levin , khlebnikov@openvz.org, xemul@parallels.com, Dave Jones , "linux-kernel@vger.kernel.org" , Andrew Morton Subject: Re: c/r: broken locking when executing map_files Message-ID: <20120505193201.GA2500@moon> References: <1335979380.10666.6.camel@lappy> <20120502172756.GD2301@moon> <20120503173125.GF19347@moon> <20120505182051.GA16029@albatros> <20120505185306.GB28746@moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120505185306.GB28746@moon> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1510 Lines: 39 On Sat, May 05, 2012 at 10:53:06PM +0400, Cyrill Gorcunov wrote: > On Sat, May 05, 2012 at 10:20:51PM +0400, Vasiliy Kulikov wrote: > ... > > > --- > > > fs/proc/base.c | 8 +++----- > > > 1 file changed, 3 insertions(+), 5 deletions(-) > > > > > > Index: linux-2.6.git/fs/proc/base.c > > > =================================================================== > > > --- linux-2.6.git.orig/fs/proc/base.c > > > +++ linux-2.6.git/fs/proc/base.c > > > @@ -2226,16 +2226,16 @@ static struct dentry *proc_map_files_loo > > > goto out; > > > > > > result = ERR_PTR(-EACCES); > > > - if (lock_trace(task)) > > > + if (!ptrace_may_access(task, PTRACE_MODE_READ)) > > > > Probably it will be better to change mutex_lock_killable() to > > mutex_lock_killable_nested() inside of lock_trace() instead of this change? > > It would keep the race-free check. > > Yup, if I'm not missing something SINGLE_DEPTH_NESTING should do the trick > for us. I'll test and report. Hmm, this doesn't work well, the mutex remanins killable so when one does | [root@neptune ~]# /proc/self/map_files/400000-419000 it sleeps forever until killed, which is not good I think. Vasiliy, could you remind me what exactly is problem if we use unlocked ptrace_may_access here? Cyrill -- 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/