linux-ext4 - Re: EXT4 ENOSPC Bug

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Date:	Tue, 17 Feb 2009 14:08:21 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>, Andres Freund <andres@...razel.de>,
	Alex Buell <alex.buell@...ted.org.uk>, adilger@....com,
	LKML <linux-kernel@...r.kernel.org>, linux-ext4@...r.kernel.org,
	Jonathan Bastien-Filiatrault <joe@....org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: EXT4 ENOSPC Bug

Eric Sandeen wrote:
> Theodore Tso wrote:
>> On Mon, Feb 16, 2009 at 04:27:03PM +0100, Andres Freund wrote:
>>> So, yes, seems to be an inode allocation problem.
>>>
>> Andres, Alex, others,
>>
>> I'm pretty sure the ENOSPC problem which you both found is an inode
>> allocation problem.  Some of you seem to have an easier time
>> reproducing it than others; could you try this patch, and periodically
>> scan your system logs for the message "ext4: find_group_flex failed,
>> fallback succeeded"?  If the problem goes away for you, and you find
>> the occasional aforemention message in your system log, that will
>> confirm what I suspect, which is the bug is in fs/ext4/inode.c's
>> find_group_flex() function.  (If I'm wrong, the fallback code will
>> activate only when the filesystem is genuinely out of inodes, which
>> should be very rare.)
>>
>> More comments are in the patch header.  My current long-term plan for
>> dealing with this is to enhance find_group_orlov() to and
>> find_group_other() to understand about flex_bg's.
> 
> Ok, I finally got to where I can reliably hit this.  Just as I was about
> to install an ext4 with this patch in place, and the bug was preventing
> the new initrd creation ;)  But worked around that, and:
> 
> ext4: find_group_flex failed, fallback succeeded dir 258402
> ext4: find_group_flex failed, fallback succeeded dir 258402
> ext4: find_group_flex failed, fallback succeeded dir 258402
> ext4: find_group_flex failed, fallback succeeded dir 258402
> ....
> 
> I'll see if I can dig a bit more as to why the find_group_flex failed,
> if you think it's worth it, Ted.

FWIW my problem seems to be different than others have encountered; mine
persists past reboot, while other reporters have said that a reboot
(remount) makes the problem go away.

I seem to be encountering some silliness in find_group_flex when 2 out
of 3 groups are full (I "only" have 55k inodes left, all in the last group).

-Eric
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