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 S1752870Ab3BUAUS (ORCPT <rfc822;w@1wt.eu>);
	Wed, 20 Feb 2013 19:20:18 -0500
Received: from mail.linuxfoundation.org ([140.211.169.12]:41868 "EHLO
	mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751943Ab3BUAUR (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 20 Feb 2013 19:20:17 -0500
Date: Wed, 20 Feb 2013 16:20:15 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Mandeep Singh Baines <msb@chromium.org>
Cc: linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>,
        Tejun Heo <tj@kernel.org>, "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [PATCH v4] lockdep: check that no locks held at freeze time
Message-Id: <20130220162015.545ebb6b.akpm@linux-foundation.org>
In-Reply-To: <CACBanvr+1VEM6UqfNVx+KiuehZejwqpGp6djPN5kTgYD-umP2g@mail.gmail.com>
References: <20130220223013.GA15760@redhat.com>
	<1361402236-28644-1-git-send-email-msb@chromium.org>
	<20130220152446.a65ff84f.akpm@linux-foundation.org>
	<CACBanvr+1VEM6UqfNVx+KiuehZejwqpGp6djPN5kTgYD-umP2g@mail.gmail.com>
X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-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
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 20 Feb 2013 16:17:39 -0800
Mandeep Singh Baines <msb@chromium.org> wrote:

> On Wed, Feb 20, 2013 at 3:24 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Wed, 20 Feb 2013 15:17:16 -0800
> > Mandeep Singh Baines <msb@chromium.org> wrote:
> >
> >> We shouldn't try_to_freeze if locks are held.
> >>
> >> ...
> >>
> >> @@ -43,6 +44,9 @@ extern void thaw_kernel_threads(void);
> >>
> >> +     if (!(current->flags & PF_NOFREEZE))
> >> +             debug_check_no_locks_held(current,
> >> +
> >>                                         "lock held while trying to freeze");
> >> ...
> >>
> >> +     debug_check_no_locks_held(tsk, "lock held at task exit time");
> >
> > There doesn't seem much point in adding the `msg' to
> > debug_check_no_locks_held() - the dump_stack() in
> > print_held_locks_bug() will tell us the same thing.  Maybe just change
> 
> dump_stack() can be confusing when there is inlining. On occasion I've
> looked at the wrong mutex_lock, for example, when there was another
> mutex_lock that was inlined. Of course, you can start objdump and
> verify the offsets. But that requires that you have the object file.
> You could have a try_to_freeze added to do_exit. I was thinking of
> adding another locks_held in the return from syscall path.

Backtraces aren't *that* bad.  We'll easily be able to tell which of
the two callsites triggered the trace.