linux-kernel - Re: 2.6.25 md oops during boot.

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Message-ID: <18503.8514.710121.995152@notabene.brown>
Date:	Thu, 5 Jun 2008 09:12:02 +1000
From:	Neil Brown <neilb@...e.de>
To:	Dave Jones <davej@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.25 md oops during boot.

On Wednesday June 4, davej@...hat.com wrote:
> Hi Neil,
>  Here's an odd one.
> https://bugzilla.redhat.com/show_bug.cgi?id=442204
> 
> Slightly old (.25-rc8-git7), but I don't recall anything changing between
> then and .25 final that could explain this.
> 
> 	Dave

Hi Dave.

Yes, Odd.

It appear that sysfs_addrm_start is being called with parent_sd == NULL.

That implies that sysfs_create_dir is being given a kobj where
->parent is non-NULL, and ->parent->sd is NULL.

So kobject_add is being given a parent with a NULL ->sd.

So in bind_rdev_to_array,  mddev->kobj.sd is NULL.

So in md_probe, either kobject_init_and_add is failing
to set up ->sd properly (which should result in an error message
   "md: cannot register md0/md - name in use"
) or alloc_disk is failing.

The most likely scenario is that alloc_disk is failing, so the
md_probe call in autorun_devices (line 3804 of md.c) fails.
The following mddev_find creates a new mddev which is not properly
initialised and gets used.

I wouldn't say this is a likely scenario as it requires (I think)
kmalloc failure very early in boot.  But I cannot see any other
possible cause.

I'll see about getting the error paths handled better.

NeilBrown
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