linux-kernel - Re: linux-next: Tree for July 18: warning at kernel/lockdep.c:2068 trace_hardirqs_on

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Date:	Sat, 19 Jul 2008 15:41:11 -0700
From:	Greg KH <gregkh@...e.de>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Mariusz Kozlowski <m.kozlowski@...land.pl>,
	Dave Hansen <haveblue@...ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	kernel-testers@...r.kernel.org, linux-next@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: linux-next: Tree for July 18: warning at kernel/lockdep.c:2068
	trace_hardirqs_on_caller

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@...e.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@...il.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@...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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