Date: Sat, 19 Jul 2008 15:41:11 -0700
From: Greg KH <gregkh@suse.de>
To: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Mariusz Kozlowski <m.kozlowski@tuxland.pl>,
       Dave Hansen <haveblue@us.ibm.com>,
       Stephen Rothwell <sfr@canb.auug.org.au>, kernel-testers@vger.kernel.org,
       linux-next@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
       Pekka Enberg <penberg@cs.helsinki.fi>
Subject: Re: linux-next: Tree for July 18: warning at kernel/lockdep.c:2068
	trace_hardirqs_on_caller
Message-ID: <20080719224111.GA6012@suse.de>
References: <20080718195352.e562a00f.sfr@canb.auug.org.au> <200807190928.33978.m.kozlowski@tuxland.pl> <19f34abd0807190255x304173d4wf2bfabb2d5bce511@mail.gmail.com> <19f34abd0807190559y2fe5ebf9h7095793e82de3122@mail.gmail.com> <20080719221723.GB5578@suse.de> <19f34abd0807191527u61c5ed61kffe2279c8d46915d@mail.gmail.com>
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On Sun, Jul 20, 2008 at 12:27:26AM +0200, Vegard Nossum wrote:
> On Sun, Jul 20, 2008 at 12:17 AM, Greg KH <gregkh@suse.de> wrote:
> > On Sat, Jul 19, 2008 at 02:59:12PM +0200, Vegard Nossum wrote:
> >> On Sat, Jul 19, 2008 at 11:55 AM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
> >> > What I don't get here is how SLUB can be used this early in the boot
> >> > process. Notice that this is still miles away from the
> >> >
> >> >    SLUB: Genslabs=12, HWalign=128, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> >> >
> >> > line, which comes much later. And that kobject_init() _is_ calling
> >> > kzalloc() via verify_dynamic_kobject_allocation(). Isn't this an
> >> > error?
> >> >
> >> > (Unfortunately, my "git log" doesn't turn up any recent changes for
> >> > any of the affected code paths here.)
> >>
> >> Ehe... and this is the reason why: The code was added by this patch:
> >>
> >> commit 0e3638d1e04040121af00195f7e4628078246489
> >> Author: Dave Hansen <haveblue@us.ibm.com>
> >> Date:   Thu Mar 16 17:30:16 2006 -0800
> >>
> >>     warn when statically-allocated kobjects are used
> >>
> >> ..which only exists in -next. Is that just a truly ancient patch, or
> >> did somebody forget to adjust their clock?
> >
> > It is truely a very old patch, that only lives in my tree, and currently
> > isn't planned to go to Linus any year soon.
> >
> > But it has a very long history of living in the -mm tree, and finding
> > real bugs, it's just not "safe" enough to go to Linus's tree.  Unless
> > you think it is?
> 
> Hm. In this case, the patch is not even reporting a problem, it is in
> fact in error itself.
> 
> The problem is that it calls kzalloc() before the slab caches have
> been set up. (Yes, it's a wonder that nothing crashed.) I can only
> suggest the addendum
> 
>     if (!slab_is_available())
>         return;

That's odd, what changed to cause this to become a problem?  Is a
kobject somehow now being created too early in the boot process than it
was in the past?  This code hasn't changed in a very long time, so I'm
loath to blame this code, odds are the root cause is somewhere else...

thanks,

greg k-h
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