linux-kernel - Re: /proc/vmcore mmap() failure issue

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Date:	Wed, 20 Nov 2013 09:59:01 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
Cc:	"bhe@...hat.com" <bhe@...hat.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"d.hatayama@...fujitsu.com" <d.hatayama@...fujitsu.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"dyoung@...hat.com" <dyoung@...hat.com>,
	"chaowang@...hat.com" <chaowang@...hat.com>
Subject: Re: /proc/vmcore mmap() failure issue

On Wed, Nov 20, 2013 at 05:29:16AM +0000, Atsushi Kumagai wrote:
> On 2013/11/18 22:56:10, kexec <kexec-bounces@...ts.infradead.org> wrote:
> > On Mon, Nov 18, 2013 at 12:51:39AM +0000, Atsushi Kumagai wrote:
> > 
> > [..]
> > > > Is there any chance that you could look into fixing this. I have no 
> > > > experience writing code for makedumpfile.
> > > 
> > > I'll send a patch to fix this soon.
> > 
> > Thanks Atsushi.
> > 
> > Vivek
> 
> Vivek, could you test this patch ?
> 
> Thanks
> Atsushi Kumagai
> 
> 
> From: Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
> Date: Wed, 20 Nov 2013 10:05:03 +0900
> Subject: [PATCH] Disable mmap() for reading fractional pages.
> 
> Since mmap() was introduced on /proc/vmcore, it fails
> for fractional pages which don't start or end at page boundary
> due to kernel issue.
> This patch disables mmap() temporarily for fractional pages
> to avoid this issue, so mmap() will be used only for aligned pages.
> 
> Signed-off-by: Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>

Hi Atsushi,

Even with this patch applied I see mmap() failure.

mem_map (39)
  mem_map    : ffffea0004e00000
  pfn_start  : 138000
  pfn_end    : 140000
read /proc/vmcore with mmap()
Excluding unnecessary pages        : [100.0 %] |STEP [Excluding
unnecessary pages] : 0.035925 seconds
Excluding unnecessary pages        : [100.0 %] \STEP [Excluding
unnecessary pages] : 0.035774 seconds
Excluding unnecessary pages        : [100.0 %] -STEP [Excluding
unnecessary pages] : 0.035229 seconds
Copying data                       : [ 40.9 %] -Can't map
[b98fd000-b9cfd000] with mmap()
read_from_vmcore: Can't read the dump memory(/proc/vmcore) with mmap().
readpage_elf: Can't read the dump memory(/proc/vmcore).
readmem: type_addr: 1, addr:bffba000, size:4096
read_pfn: Can't get the page data.
 Resource temporarily unavailable
makedumpfile Failed.
kdump: saving vmcore failed

Following is part of /proc/iomem on my system.

00100000-bffc283f : System RAM
  01000000-018c551d : Kernel code
  018c551e-01ef3f3f : Kernel data
  0204a000-02984fff : Kernel bss
  2e000000-35ffffff : Crash kernel
bffc2840-bfffffff : reserved

This is a different system than what I used last time. So I am not sure
if this is same error or something else. But one thing is clear that
System RAM last page is partial and we should face mmap() failure.

Thanks
Vivek
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