linux-kernel - Re: [PATCH] [v4] PM / hibernate: Fix hibernation panic caused by inconsistent e820 map

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Message-ID: <20151004151540.GB12607@xo-6d-61-c0.localdomain>
Date:	Sun, 4 Oct 2015 17:15:41 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Chen, Yu C" <yu.c.chen@...el.com>
Cc:	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"Brown, Len" <len.brown@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	"jlee@...e.com" <jlee@...e.com>,
	"joeyli.kernel@...il.com" <joeyli.kernel@...il.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] [v4] PM / hibernate: Fix hibernation panic caused by
 inconsistent e820 map

Hi!
> > > > 3) I'm not sure I understand the changelog correctly. What happens
> > > > when BIOS reports less memory on hibernation? Will you magically
> > > > remove memory from kernel at runtime? Will /proc/meminfo be invalid
> > after resume?
> > > > Will all the memory management tuning need fixing?
> > > >
> > > Oh, I did not notice it before. So deleting the logic of '
> > > info->num_physpages != get_num_physpages()' is not suitable.
> > > The subset relationship should not be considered in this patch.
> > 
> > Ok. So... if you really want, you can add some messages like "hey, this is bios
> > bug, maybe updating bios is a good idea".. but please lets keep the original
> > logic.
> > 
> OK. I see, I'll not change its original code.
> So can I add a function here that checks if current BIOS  e820 map is 
> strictly the same as it was before S4?  If it is not the same, we will print some warnnings
> , and if we panic later, we will print that , the panic reason might be due to broken BIOS.
> I think I can archive this by putting  the e820_saved array  into struct swsusp_info, 
>  and pass it to second kernel: 
> struct swsusp_info will always occupy one page size, and has a lot of extra space left,
> meanwhile the total size of e820 map will not exceed the PAGE_SIZE currently, it's safe 
> to put it in struct swsusp_info.
> 
> And this does not need much changing of current code. What do you think? Thanks.

Can we simply add explanation printk() before the panic(), without any other changes?
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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