From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755608AbbICNso (ORCPT <rfc822;w@1wt.eu>);
	Thu, 3 Sep 2015 09:48:44 -0400
Received: from h2.hallyn.com ([78.46.35.8]:51799 "EHLO h2.hallyn.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1755487AbbICNsl (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 3 Sep 2015 09:48:41 -0400
Date: Thu, 3 Sep 2015 08:48:39 -0500
From: "Serge E. Hallyn" <serge@hallyn.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>, Felipe Balbi <balbi@ti.com>,
        James Morris <james.l.morris@oracle.com>, serge@hallyn.com,
        linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linux OMAP Mailing List <linux-omap@vger.kernel.org>
Subject: Re: [PATCH v2] security: device_cgroup: fix RCU lockdep splat
Message-ID: <20150903134839.GB8834@mail.hallyn.com>
References: <20150902125608.GA8299@saruman.tx.rr.com>
 <1441199548-29633-1-git-send-email-balbi@ti.com>
 <20150902162450.GJ22326@mtj.duckdns.org>
 <20150903001433.GB4029@linux.vnet.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150903001433.GB4029@linux.vnet.ibm.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Sep 02, 2015 at 05:14:33PM -0700, Paul E. McKenney wrote:
> On Wed, Sep 02, 2015 at 12:24:50PM -0400, Tejun Heo wrote:
> > cc'ing Paul.
> > 
> > On Wed, Sep 02, 2015 at 08:12:28AM -0500, Felipe Balbi wrote:
> > > while booting AM437x device, the following splat
> > > triggered:
> > > 
> > > [   12.005238] ===============================
> > > [   12.009749] [ INFO: suspicious RCU usage. ]
> > > [   12.014116] 4.2.0-next-20150831 #1154 Not tainted
> > > [   12.019050] -------------------------------
> > > [   12.023408] security/device_cgroup.c:405 device_cgroup:verify_new_ex called without proper synchronization!
> > ...
> > > [   12.128326] [<c0317a04>] (verify_new_ex) from [<c0317f50>] (devcgroup_access_write+0x374/0x658)
> > > [   12.137426] [<c0317f50>] (devcgroup_access_write) from [<c00d2800>] (cgroup_file_write+0x28/0x1bc)
> > > [   12.146796] [<c00d2800>] (cgroup_file_write) from [<c01f1670>] (kernfs_fop_write+0xc0/0x1b8)
> > > [   12.155620] [<c01f1670>] (kernfs_fop_write) from [<c0177c94>] (__vfs_write+0x1c/0xd8)
> > > [   12.163783] [<c0177c94>] (__vfs_write) from [<c0178594>] (vfs_write+0x90/0x16c)
> > > [   12.171426] [<c0178594>] (vfs_write) from [<c0178db4>] (SyS_write+0x44/0x9c)
> > > [   12.178806] [<c0178db4>] (SyS_write) from [<c000f680>] (ret_fast_syscall+0x0/0x1c)
> > 
> > This shouldn't be happening because devcgroup_access_write() always
> > grabs devcgroup_mutex.  Looking at the log, the culprit seems to be
> > f78f5b90c4ff ("rcu: Rename rcu_lockdep_assert() to
> > RCU_LOCKDEP_WARN()").  It missed the bang for the second test while
> > inverting it, so adding rcu_read_lock() isn't the right fix here.
> > 
> > Paul, can you please fix it?
> 
> Gah!  Please see below.
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> security/device_cgroup: Fix RCU_LOCKDEP_WARN() condition
> 
> f78f5b90c4ff ("rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()")
> introduced a bug by incorrectly inverting the condition when moving from
> rcu_lockdep_assert() to RCU_LOCKDEP_WARN().  This commit therefore fixes
> the inversion.
> 
> Reported-by: Felipe Balbi <balbi@ti.com>
> Reported-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Serge Hallyn <serge@hallyn.com>

Oh, makes sense :)  (didn't see the original patch when it came by, sorry)

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 73455089feef..03c1652c9a1f 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -401,7 +401,7 @@ static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
>  	bool match = false;
>  
>  	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
> -			 lockdep_is_held(&devcgroup_mutex),
> +			 !lockdep_is_held(&devcgroup_mutex),
>  			 "device_cgroup:verify_new_ex called without proper synchronization");
>  
>  	if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {