linux-ext4 - ocfs2 inconsistent when updating journal superblock failed

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Date:	Tue, 2 Jun 2015 15:47:56 +0800
From:	Joseph Qi <joseph.qi@...wei.com>
To:	"ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>,
	<linux-ext4@...r.kernel.org>
Subject: ocfs2 inconsistent when updating journal superblock failed

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.

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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