linux-kernel - Re: Boot problem on PPC with 4.4-git

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Message-ID: <569FFDC7.8020002@lwfinger.net>
Date:	Wed, 20 Jan 2016 15:36:07 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Boot problem on PPC with 4.4-git - Bisected to commit 21266be

On 01/20/2016 02:33 PM, Dan Williams wrote:
> On Wed, Jan 20, 2016 at 12:16 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>> On Wed, Jan 20, 2016 at 12:08 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>>> On Wed, Jan 20, 2016 at 12:01 PM, Larry Finger
>>> <Larry.Finger@...inger.net> wrote:
>>>> My PowerBook G4 Aluminum with a 32-bit PPC processor fails to boot for the
>>>> 4.4-git series. The problem was bisected to commit 21266be. It took a while
>>>> to figure out why a commit that only rearranges the Kconfig files could
>>>> cause the problem.
>>>>
>>>> The answer came when I read the commit message for 90a545e98126 and saw that
>>>> "Recompiling with CONFIG_IO_STRICT_DEVMEM=n" might be necessary. After I
>>>> made that change, the system boots.
>>>>
>>>> If it is the graphics hardware driver at fault, the VGA controller is listed
>>>> as an ATI RV350 [Mobility Radeon 9600 M10] with PCI ID 1002:4350. It uses
>>>> radeon as the driver.
>>>>
>>>> I'm not sure if this is a bug in the configuration, but I know that
>>>> selecting the default answer to all the new configuration parameters leaves
>>>> me with a machine that is unbootable.
>>>
>>> I agree that the default configuration should remain bootable.  I'll
>>> send a change that does not force that default.
>>>
>>> Thanks for the report and sorry for the inconvenience.
>>
>> Are you sure that the bisect is pointing to "21266be9ed54 arch:
>> consolidate CONFIG_STRICT_DEVM in lib/Kconfig.debug" and not
>> "90a545e98126 restrict /dev/mem to idle io memory ranges"?  The
>> default for CONFIG_STRICT_DEVM should be unchanged in 21266be9ed54,
>> it's not until 90a545e98126 that I would expect a behavior change.
>
> Sorry for the mail flurry... if you can verify that the following
> change resolves this problem I'll send it up:
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index f75a33f29f6e..7d0b49c536c5 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1919,7 +1919,6 @@ config STRICT_DEVMEM
> config IO_STRICT_DEVMEM
>         bool "Filter I/O access to /dev/mem"
>         depends on STRICT_DEVMEM
> -       default STRICT_DEVMEM
>         ---help---
>           If this option is disabled, you allow userspace (root) access to all
>           io-memory regardless of whether a driver is actively using that

That isn't quite right. I added that patch, and restored the 4.4.0 
configuration. That one has "CONFIG_STRICT_DEVM=y". After I ran "make 
oldconfig", CONFIG_STRICT_DEVM was still set, which kills rebooting.

When I repeated the process, but removed the CONFIG_STRICT_DEVM line from 
.config before I ran "make oldconfig", then I got a bootable configuration. It 
seems that once STRICT_DEVM is yes, only a "make menuconfig", or equivalent, 
will let you turn it off.

Larry