linux-kernel - Re: kernel boot fail with efi earlyprintk (bisected)

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Date:	Mon, 25 Aug 2014 17:06:19 +0800
From:	Dave Young <dyoung@...hat.com>
To:	"Zheng, Lv" <lv.zheng@...el.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	"Fleming, Matt" <matt.fleming@...el.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...ica.org" <devel@...ica.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"Moore, Robert" <robert.moore@...el.com>
Subject: Re: kernel boot fail with efi earlyprintk (bisected)

On 08/25/14 at 06:34am, Zheng, Lv wrote:
> Hi,
> 
> > From: Dave Young [mailto:dyoung@...hat.com]
> > Sent: Monday, August 25, 2014 2:07 PM
> > To: Matt Fleming
> > Cc: Zheng, Lv; Fleming, Matt; linux-efi@...r.kernel.org; linux-acpi@...r.kernel.org; linux-kernel@...r.kernel.org; devel@...ica.org;
> > lenb@...nel.org; Wysocki, Rafael J; Moore, Robert
> > Subject: Re: kernel boot fail with efi earlyprintk (bisected)
> > 
> > On 08/22/14 at 06:02pm, Dave Young wrote:
> > > On 08/21/14 at 09:52pm, Matt Fleming wrote:
> > > > On Tue, 19 Aug, at 04:16:58PM, Dave Young wrote:
> > > > > Hi,
> > > > >
> > > > > 3.16 kernel boot fail with earlyprintk=efi on my laptop.
> > > > > It keeps scrolling at the bottom line of screen.
> > > > >
> > > > > Bisected, the first bad commit is below:
> > > > > commit 86dfc6f339886559d80ee0d4bd20fe5ee90450f0
> > > > > Author: Lv Zheng <lv.zheng@...el.com>
> > > > > Date:   Fri Apr 4 12:38:57 2014 +0800
> > > > >
> > > > >     ACPICA: Tables: Fix table checksums verification before installation.
> > > > >
> > > > >
> > > > > I did some debugging by enabling both serial and efi earlyprintk, below is
> > > > > some debug dmesg, seems early_ioremap fails in scroll up function due to
> > > > > no free slot, but I'm still not sure if the debug info is right or not.
> > > >
> > > > Thanks Dave, your callstack seems to make sense.
> > > >
> > > > Can you also enable early_ioremap_debug so that we can figure out where
> > > > all the FIXMAP slots are going?
> > >
> > > With early_ioremap_debug enabled, there will be a lot of "dropped printk", so
> > > I can not get any useful information.
> > >
> > > Will try to do more debug.
> > 
> > early_ioremap_debug does not work because we are debugging early_printk but
> > early_ioremap_debug itself will print warning message at the same time.
> > 
> > Tried what Lv mentioned, increasing the early ioremap slots does help.
> 
> Could you send a tested patch to linux-acpi@...r.kermel.org for this?
> I think the number of early mapping slots need to be increased by 1 because of this case.

Problem is I do not understand the implementation detail yet.

I did below changes:

Original values:
#define NR_FIX_BTMAPS           64
#define FIX_BTMAPS_SLOTS        4

-> new values tested:
#define NR_FIX_BTMAPS           32
#define FIX_BTMAPS_SLOTS        8


There's below comments
        /*
         * 256 temporary boot-time mappings, used by early_ioremap(),
         * before ioremap() is functional.
         *
         * If necessary we round it up to the next 256 pages boundary so
         * that we can have a single pgd entry and a single pte table:
         */

So seems increase it to 64 * 8 = 512 should be ok. If it's fine I can test again
and post a patch.


Thanks
Dave
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