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

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Date:	Sun, 20 Jul 2008 15:03:41 +0200
From:	Bernhard Walle <bwalle@...e.de>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Vegard Nossum <vegard.nossum@...il.com>, Greg KH <gregkh@...e.de>,
	Mariusz Kozlowski <m.kozlowski@...land.pl>,
	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>,
	Ingo Molnar <mingo@...e.hu>, Vivek Goyal <vgoyal@...hat.com>,
	kexec <kexec@...ts.infradead.org>
Subject: Re: linux-next: Tree for July 18: warning at kernel/lockdep.c:2068
 trace_hardirqs_on_caller

* Dave Hansen <dave@...ux.vnet.ibm.com> [2008-07-20 02:01]:
>
> It is possible that it could run later.  But, I do know that there are
> at least a couple of these tables (on various arches) that we toss out
> of memory or become unavailable later in boot.  
> 
> I do this this:
> 
>     sysfs: add /sys/firmware/memmap
> 
> is really being done at the wrong level.

I posted that patches multiple times. They were reviewed by the kdump
maintainer and by the kexec maintainer. Why didn't you mention it
*there* that this is the wrong way?

> I don't, for instance, see
> *any* reference to memory hotplug in these patches.

Right. The idea was to add memory hotplugging later. I decided to
create the patch series, get some review, and then fix the rest of the
systems that use memory hot-plugging. So, do you see a problem (in
theory) to add memory and remove memory in that sysfs interface? Of
course the code must be extended to handle modifications in the linked
list afterwards. Yes, I should have made that extension just after the
patch went into tip. Unfortunately, I didn't have time so far.

> Secondly, why don't we just modify the existing /sys/devices/system/memory

Because I didn't know that interface. And because I don't see that
interface on my two systems that I just checked. i386 and x86-64. What
do I have to do to enable that interface?

Does that interface export the *used* memory or just export the memory
that is available? Because exactly that was the reason why I made that
modification -- because kexec needs to know the *available* memory even
if that memory is disabled via 'memmap' or 'mem' command line
parameters.

Bernhard
-- 
Bernhard Walle, SUSE LINUX Products GmbH, Architecture Development
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