linux-kernel - Re: S4 resume broken since 2.6.39 (3.1, too)

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Date:	Mon, 26 Sep 2011 19:34:33 -0700
From:	Yinghai Lu <yinghai.lu@...cle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Takashi Iwai <tiwai@...e.de>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, oneukum@...e.de, x86@...nel.org,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: S4 resume broken since 2.6.39 (3.1, too)

On 09/26/2011 03:24 PM, Rafael J. Wysocki wrote:

> On Thursday, September 22, 2011, Yinghai Lu wrote:
>> On Wed, Sep 21, 2011 at 11:48 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>>> It looks like init_memory_mapping() is sometimes called with "end"
>>> beyond the last mapped PFN and it explodes when we try to write stuff to
>>> that address during image restoration.
>>>
>>> IOW, the Yinghai's assumption that init_memory_mapping() would always be
>>> called with a "good end" on x86_64 was overomptimistic.
>>
>> for 64bit x86, kernel_physical_mapping_init() will use
>> map_low_page()/call early_memmap() to access ram for page_table that is above
>> rather last mapped PFN.
>>
>> the point is:
>> on system with 64g, usable ram will be [0,2048m), [4g, 64g)
>> init_memory_mapping will be called two times for them.
>> before putting page_table high,
>> page table will be two parts: one is just below 512M, and one below 2048m.
>> after putting page_table high,
>> page table will be two parts: one is just below 2048M, and one below 64G.
>>
>> one of the purposes is finding biggest continuous big range under
>> 1024m for kdump.
> 
> This is all fine so long as we can ensure that the "end" value we're
> passing to init_memory_mapping() will always be a valid address, which
> evidently is not the case sometimes.


I don't understand why end is not valid could happen.

end should be always valid address. one is max_low_pfn under 4g, and another one is max_pfn...


> 
> So, in my opinion we should simply apply the Takashi's patch at this
> point and revisit the kdump issue later, when we actually know how to do
> the right thing.


Takashi said: 2.6.37 with that commit is ok, only 2.6.39 somehow has the 1/20 chance has the reset problem.

so that commit should not the cause. could be some hidden assumption from restore code ? 

Yinghai
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