linux-ext4 - Re: Filesystem corruption after unreachable storage

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Date:   Fri, 28 Feb 2020 12:06:17 +0100
From:   Jean-Louis Dupond <jean-louis@...ond.be>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: Filesystem corruption after unreachable storage

On 25/02/2020 18:23, Theodore Y. Ts'o wrote:
> On Tue, Feb 25, 2020 at 02:19:09PM +0100, Jean-Louis Dupond wrote:
>> FYI,
>>
>> Just did same test with e2fsprogs 1.45.5 (from buster backports) and kernel
>> 5.4.13-1~bpo10+1.
>> And having exactly the same issue.
>> The VM needs a manual fsck after storage outage.
>>
>> Don't know if its useful to test with 5.5 or 5.6?
>> But it seems like the issue still exists.
> This is going to be a long shot, but if you could try testing with
> 5.6-rc3, or with this commit cherry-picked into a 5.4 or later kernel:
>
>     commit 8eedabfd66b68a4623beec0789eac54b8c9d0fb6
>     Author: wangyan <wangyan122@...wei.com>
>     Date:   Thu Feb 20 21:46:14 2020 +0800
>
>         jbd2: fix ocfs2 corrupt when clearing block group bits
>         
>         I found a NULL pointer dereference in ocfs2_block_group_clear_bits().
>         The running environment:
>                 kernel version: 4.19
>                 A cluster with two nodes, 5 luns mounted on two nodes, and do some
>                 file operations like dd/fallocate/truncate/rm on every lun with storage
>                 network disconnection.
>         
>         The fallocate operation on dm-23-45 caused an null pointer dereference.
>         ...
>
> ... it would be interesting to see if fixes things for you.  I can't
> guarantee that it will, but the trigger of the failure which wangyan
> found is very similar indeed.
>
> Thanks,
>
> 						- Ted
Unfortunately it was a too long shot :)

Tested with a 5.4 kernel with that patch included, and also with 5.6-rc3.
But both had the same issue.

- Filesystem goes read-only when the storage comes back
- Manual fsck needed on bootup to recover from it.

It would be great if we could make it not corrupt the filesystem on 
storage recovery.
I'm happy to test some patches if they are available :)

Thanks
Jean-Louis