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

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Message-ID: <0910DD04CBD6DE4193FCF86B9C00BE971BF592@BPXM01GP.gisp.nec.co.jp>
Date:	Mon, 18 Nov 2013 00:51:39 +0000
From:	Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
To:	"vgoyal@...hat.com" <vgoyal@...hat.com>
CC:	"d.hatayama@...fujitsu.com" <d.hatayama@...fujitsu.com>,
	"bhe@...hat.com" <bhe@...hat.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"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

(2013/11/15 23:26), Vivek Goyal wrote:
> On Fri, Nov 15, 2013 at 06:41:52PM +0900, HATAYAMA Daisuke wrote:
>
> [..]
>>> Given the fact that hpa does not like fixing it in kernel. We are left
>>> with option of fixing it in following places.
>>>
>>> - Drop partial pages in kexec-tools
>>> - Drop partial pages in makeudmpfile.
>>> - Read partial pages using read() interface in makedumpfile
>>> - Modify /proc/vmcore to copy partial pages in second kernel's memory.
>>>
>>> It is not clear to me that partial pages are really useful.  So I want
>>> to avoid modifying /proc/vmcore to deal with partial pages and increase
>>> complexity.
>>>
>>> So fixing makedumpfile (either option2 or option 3) seems least risky
>>> to me. In fact I would say let us keep it simple and truncate partial
>>> pages in makedumpfile to keep it simple. And look at option 3 once we
>>> have a strong use case for partial pages.
>>>
>>> What do you think?
>>>
>>
>> As you say, it's not clear that partial pages are really useful, but on
>> the other hand, it seems to me not clear that they are really useless.
>> I think we should get them as long as we have access to them.
>>
>> It seems best to me the option 3). Switching between read and mmap would
>> be not so complex and also it's by far flexible in makedumpfile than in
>> kernel.
>
> Ok, I am fine with option 3. It is more complicated option but safe
> option.

It sounds reasonable also to me.

> 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 Kumagai
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