IO memory read from /proc/vmcore leads to hang.

Daniel Walker danielwa at
Thu Jul 21 08:19:43 PDT 2016

  There appears to be no code which checks what is or is not System ram, 
there is nothing that checks the device tree to see what is IO memory, 
and nothing reads /proc/iomem .. So AFAIK nothing cares if it's IO 
memory, or system ram, and there's no method to config things to skip 
any memory in the system, except in makedumpfile which can skip symbols 
not IO memory.

On 07/21/2016 12:34 AM, Maxim Uvarov wrote:
> Second kernel should already know that it's not system ram of the
> first kernel and in that case makedumpfile will not dump that memory.
> Simple way is to pass additional kernel argument to kexec is when you
> load the kernel. If it works than you can think how it's better to
> pass this parameter.  Variants might be request_resource() in first
> kernel or add some logic to kexec tools.
> Best regards,
> Maxim.
> 2016-07-20 22:18 GMT+03:00 Daniel Walker <danielwa at>:
>> Mahesh, I didn't get your email for some reason . I saw it in the Archives.
>> makedumpfile doesn't appear to have a way to drop free form memory areas. So
>> I need to drop 00800000 to 00807fff , but I don't see a way to do that. Any
>> other suggestions on how to prevent this hang ?
>> On 07/11/2016 02:46 PM, Daniel Walker wrote:
>>> Hi,
>>> I found found that on my Powerpc machine there is some IO memory which
>>> will cause the box to hang if I read it. It's a custom device that was added
>>> to the board for a special purpose.
>>> I was looking for a way to exclude this memory from the dump, and while
>>> doing that I found that kexec makes a list of memory segments that go into
>>> the core file. I was wondering why most of the kexec architecture don't
>>> appear to exclude device memory like what's listed in /proc/iomem.
>>> Is there a good reason why that's not the case?
>>> Daniel
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