linux-kernel - Re: linux-next: Tree for Jan 20 -- Kernel panic

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Message-ID: <54BFAA5D.4040108@roeck-us.net>
Date:	Wed, 21 Jan 2015 05:32:13 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Sabrina Dubroca <sd@...asysnail.net>,
	Al Viro <viro@...IV.linux.org.uk>
CC:	Paul Moore <pmoore@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-audit@...hat.com,
	Richard Guy Briggs <rgb@...hat.com>
Subject: Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount
 root fs

On 01/21/2015 03:05 AM, Sabrina Dubroca wrote:
> 2015-01-21, 04:36:38 +0000, Al Viro wrote:
>> On Tue, Jan 20, 2015 at 08:01:26PM -0800, Guenter Roeck wrote:
>>> With this patch:
>>>
>>> sys_mkdir .:40775 returned -17
>>> sys_mkdir usr:40775 returned 0
>>> sys_mkdir usr/lib:40775 returned 0
>>> sys_mkdir usr/share:40755 returned 0
>>> sys_mkdir usr/share/udhcpc:40755 returned 0
>>> sys_mkdir usr/bin:40775 returned 0
>>> sys_mkdir usr/sbin:40775 returned 0
>>> sys_mkdir mnt:40775 returned 0
>>> sys_mkdir proc:40775 returned 0
>>> sys_mkdir root:40775 returned 0
>>> sys_mkdir lib:40775 returned 0
>>> sys_mkdir lib/modules:40775 returned 0
>>> ...
>>>
>>> and the problem is fixed.
>
> This patch also works for me.
>
>
>> ... except that it simply confirms that something's fishy with getname_kernel()
>> of ->name of struct filename returned by getname().  IOW, I still do not
>> understand the mechanism of breakage there.
>
> I'm not so sure about that.  I tried to copy name to a new string in
> do_path_lookup and that didn't help.
>
> Now, I've removed the
>
>          putname(filename);
>
> line from do_path_lookup and I don't get the panic.
>
>
> And BTW, I added Guenter's debugging to init/initramfs.c and got:
> sys_mkdir dev:40755 returned 0
> sys_mkdir root:40700 returned 0
>
> even if it ends up panic'ing.
>
Another data point (though I have no idea if it is useful or what it means):

In the working case, path_init sets nd->flags to 0x50 or 0x51.
In the non-working case (ie for all files with a '/' in the name),
it sets nd->flags to 0x10 or 0x11, even though it is always called
with the LOOKUP_RCU bit set in flags.

Guenter

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