linux-kernel - Re: kdump broken on 2.6.37-rc4

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Date:	Fri, 17 Dec 2010 18:51:28 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On Fri, Dec 17, 2010 at 03:34:05PM -0500, Vivek Goyal wrote:
> On Fri, Dec 17, 2010 at 12:06:23PM -0800, Yinghai Lu wrote:
> > On 12/17/2010 12:01 PM, Vivek Goyal wrote:
> > > On Fri, Dec 17, 2010 at 11:52:11AM -0800, Yinghai Lu wrote:
> > >> On 12/17/2010 11:50 AM, Vivek Goyal wrote:
> > >>> On Fri, Dec 17, 2010 at 11:46:08AM -0800, Yinghai Lu wrote:
> > >>>> On 12/17/2010 11:39 AM, H. Peter Anvin wrote:
> > >>>>> On 12/17/2010 10:21 AM, Yinghai Lu wrote:
> > >>>>>>>>
> > >>>>>>>> Do we have actual testing for how high the 64-bit kernel will load?
> > >>>>>>>
> > >>>>>>> I will do some experiments on my box today and let you know.
> > >>>>>>
> > >>>>>> if bzImage is used, it is 896M.
> > >>>>>>
> > >>>>>
> > >>>>> Why?  896 MiB is a 32-bit kernel limitation which doesn't have anything
> > >>>>> to do with the bzImage format.
> > >>>>>
> > >>>>> So unless there is something going on here, I suspect you're just plain
> > >>>>> flat wrong.
> > >>>>
> > >>>> kexec-tools have some checking when it loads bzImage.
> > >>>>
> > >>>
> > >>> Yinghai,
> > >>>
> > >>> I think x86_64 might have just inherited the settings of 32bit without
> > >>> giving it too much of thought. At that point of time nobody bothered
> > >>> to load the kernel from high addresses. So these might be artificial
> > >>> limits.
> > >>
> > >> good point.  will check that.
> > > 
> > > Yinghai,
> > > 
> > > On x86_64, I am not seeing "Crash kernel" entry in /proc/iomem.
> > > 
> > > I see following in dmesg.
> > > 
> > > "[    0.000000] Reserving 128MB of memory at 64MB for crashkernel (System
> > > RAM: 5120MB)"
> > > 
> > > Following is my /proc/iomem.
> > > 
> > > # cat /proc/iomem 
> > > 00000100-0000ffff : reserved
> > > 00010000-00096fff : System RAM
> > > 00097000-0009ffff : reserved
> > > 000c0000-000e7fff : pnp 00:0f
> > > 000e8000-000fffff : reserved
> > > 00100000-bffc283f : System RAM
> > >   01000000-015d1378 : Kernel code
> > >   015d1379-01aee00f : Kernel data
> > >   01bc8000-024b4c4f : Kernel bss
> > > bffc2840-bfffffff : reserved
> > > 
> > > So there is RAM available at the requested address still no entry for
> > > "Crash Kernel". This is both with 2.6.36 as well as 37-rc6 kernel. I am 
> > > wondering if insert_resource() is failing here?
> > > 
> > 
> > also could be memblock_x86_reserve() fail ...
> > 
> > Please check attached debug patch...
> > 
> 
> looks like memblock_x86_reserve() is fine. Following is dmesg output with
> your debug patches applied.

Hi Yinghai,

Please ignore this. The problem was with my setup with some user space
script setting kexec_crash_size = 0 hence freeing up the memory. I think
it is time to put a kernel message when memory is freed/shrinked. I wasted
a lot of time debugging it.

Sorry for the noise here.

thanks
Vivek
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