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

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Date:	Tue, 27 Sep 2011 19:03:14 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Yinghai Lu <yinghai.lu@...cle.com>
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 Tuesday, September 27, 2011, Yinghai Lu wrote:
> 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 ? 

Quite frankly, I doubt it.  The only remotely related change between 2.6.37
and 2.6.37 seems to be commit d1ee433 (x86, trampoline: Use the unified
trampoline setup for ACPI wakeup).

Thanks,
Rafael
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