[Ocfs2-devel] ocfs2 inconsistent when updating journal superblock failed

[Junxiao Bi]

Hi Joseph,

On 06/02/2015 03:47 PM, Joseph Qi wrote:
> Hi all,
> If jbd2 has failed to update superblock because of iscsi link down, it
> may cause ocfs2 inconsistent.
> 
> kernel version: 3.0.93
> dmesg:
> JBD2: I/O error detected when updating journal superblock for
> dm-41-36.
> 
> Case description:
> Node 1 was doing the checkpoint of global bitmap.
> ocfs2_commit_thread
>   ocfs2_commit_cache
>     jbd2_journal_flush
>       jbd2_cleanup_journal_tail
>         jbd2_journal_update_superblock
>           sync_dirty_buffer
>             submit_bh  *failed*
> Since the error was ignored, jbd2_journal_flush would return 0.
> Then ocfs2_commit_cache thought it normal, incremented trans id and woke
> downconvert thread.
> So node 2 could get the lock because the checkpoint had been done
> successfully (in fact, bitmap on disk had been updated but journal
> superblock not). Then node 2 did the update to global bitmap as normal.
> After a while, node 2 found node 1 down and began the journal recovery.
> As a result, the new update by node 2 would be overwritten and filesystem
> became inconsistent.
If this is the case, this seemed a generic issue. Assume a two node
cluster, node 1 updated global bitmap, and the transaction for this
update have been written into node 1's journal. Then node 2 updated
global bitmap, after that, node 1 crash and node 2 replay node 1's
journal and will overwrite global bitmap to old one. Do i miss some point?

Thanks,
Junxiao.

> 
> I'm not sure if ext4 has the same case (can it be deployed on LUN?).
> But for ocfs2, I don't think the error can be omitted.
> Any ideas about this?
> 
> Thanks,
> Joseph
> 
> 
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