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Subject: Re: [PATCH] ocfs2: call journal flush to mark journal as empty after
 journal recovery when mount
To:     Kai Li <li.kai4@h3c.com>, mark@fasheh.com, jlbec@evilplan.org,
        joseph.qi@linux.alibaba.com
Cc:     ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20191211100338.510-1-li.kai4@h3c.com>
From:   Changwei Ge <chge@linux.alibaba.com>
Message-ID: <d4bb15d0-55fa-2a8e-a975-4c65eed3bae3@linux.alibaba.com>
Date:   Wed, 11 Dec 2019 20:47:48 +0800
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Hi Kai,

Now the problem is more clear to me.

Just a few comments inline.

On 12/11/19 6:03 PM, Kai Li wrote:
> If journal is dirty when mount, it will be replayed but jbd2 sb
> log tail cannot be updated to mark a new start because
> journal->j_flag has already been set with JBD2_ABORT first
> in journal_init_common. When a new transaction is committed, it
> will be recored in block 1 first(journal->j_tail is set to 1 in
> journal_reset).
> 
> If emergency restart happens again before journal super block is
> updated unfortunately, the new recorded trans will not be replayed
> in the next mount.

So this issue happens before the first committing log iteration  comes 
(running in jbd2 kernel thread), right?
This leads jbd2 losing the chance to update *on-disk* journal super 
block but the dynamic status of journal is still remaining in memory.

Yes, I agree. We should update on-disk journal super block after journal 
recovery since that procedure doesn't involve journal status in memory 
which is just reset to the very beginning(tail and head pointing to the 
first block) of journal region.

Moreover, during journal recovery running by peer nodes, ocfs2 already 
does that like what this patch does.

ocfs2_recover_node() -> ocfs2_replay_journal().

Very good job to catch such an exception. :-)


> 
> This exception happens when this lun is used by only one node. If it
> is used by multi-nodes, other node will replay its journal and its
> journal sb block will be updated after recovery.
> 
> To fix this problem, use jbd2_journal_flush to mark journal as empty as
> ocfs2_replay_journal has done.
> 
> The following jbd2 journal can be generated by touching a new file after
> journal is replayed, and seq 15 is the first valid commit, but first seq
> is 13 in journal super block.
> logdump:
> Block 0: Journal Superblock
> Seq: 0   Type: 4 (JBD2_SUPERBLOCK_V2)
> Blocksize: 4096   Total Blocks: 32768   First Block: 1
> First Commit ID: 13   Start Log Blknum: 1
> Error: 0
> Feature Compat: 0
> Feature Incompat: 2 block64
> Feature RO compat: 0
> Journal UUID: 4ED3822C54294467A4F8E87D2BA4BC36
> FS Share Cnt: 1   Dynamic Superblk Blknum: 0
> Per Txn Block Limit    Journal: 0    Data: 0
> 
> Block 1: Journal Commit Block
> Seq: 14   Type: 2 (JBD2_COMMIT_BLOCK)
> 
> Block 2: Journal Descriptor
> Seq: 15   Type: 1 (JBD2_DESCRIPTOR_BLOCK)
> No. Blocknum        Flags
>   0. 587             none
> UUID: 00000000000000000000000000000000
>   1. 8257792         JBD2_FLAG_SAME_UUID
>   2. 619             JBD2_FLAG_SAME_UUID
>   3. 24772864        JBD2_FLAG_SAME_UUID
>   4. 8257802         JBD2_FLAG_SAME_UUID
>   5. 513             JBD2_FLAG_SAME_UUID JBD2_FLAG_LAST_TAG
> ...
> Block 7: Inode
> Inode: 8257802   Mode: 0640   Generation: 57157641 (0x3682809)
> FS Generation: 2839773110 (0xa9437fb6)
> CRC32: 00000000   ECC: 0000
> Type: Regular   Attr: 0x0   Flags: Valid
> Dynamic Features: (0x1) InlineData
> User: 0 (root)   Group: 0 (root)   Size: 7
> Links: 1   Clusters: 0
> ctime: 0x5de5d870 0x11104c61 -- Tue Dec  3 11:37:20.286280801 2019
> atime: 0x5de5d870 0x113181a1 -- Tue Dec  3 11:37:20.288457121 2019
> mtime: 0x5de5d870 0x11104c61 -- Tue Dec  3 11:37:20.286280801 2019
> dtime: 0x0 -- Thu Jan  1 08:00:00 1970
> ...
> Block 9: Journal Commit Block
> Seq: 15   Type: 2 (JBD2_COMMIT_BLOCK)
> 
> The following is jouranl recovery log when recovering the upper jbd2
> journal when mount again.
> syslog:
> [ 2265.648622] ocfs2: File system on device (252,1) was not unmounted cleanly, recovering it.
> [ 2265.649695] fs/jbd2/recovery.c:(do_one_pass, 449): Starting recovery pass 0
> [ 2265.650407] fs/jbd2/recovery.c:(do_one_pass, 449): Starting recovery pass 1
> [ 2265.650409] fs/jbd2/recovery.c:(do_one_pass, 449): Starting recovery pass 2
> [ 2265.650410] fs/jbd2/recovery.c:(jbd2_journal_recover, 278): JBD2: recovery, exit status 0, recovered transactions 13 to 13
> 
> Due to first commit seq 13 recorded in journal super is not consistent
> with the value recorded in block 1(seq is 14), journal recovery will be
> terminated before seq 15 even though it is an unbroken commit, inode
> 8257802 is a new file and it will be lost.
> 
> Signed-off-by: Kai Li <li.kai4@h3c.com>
> ---
>   fs/ocfs2/journal.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
> index 1afe57f425a0..b8b9d26fa731 100644
> --- a/fs/ocfs2/journal.c
> +++ b/fs/ocfs2/journal.c
> @@ -1066,6 +1066,14 @@ int ocfs2_journal_load(struct ocfs2_journal *journal, int local, int replayed)
>   
>   	ocfs2_clear_journal_error(osb->sb, journal->j_journal, osb->slot_num);
>   
> +	if (replayed) {
> +		/* wipe the journal */
> +		jbd2_journal_lock_updates(journal->j_journal);
> +		status = jbd2_journal_flush(journal->j_journal);
> +		jbd2_journal_unlock_updates(journal->j_journal);
> +		mlog(ML_NOTICE, "journal recovery complete, status=%d", status);

Is the above mlog line necessary?
Can we just log a warning only jbd2_journal_flush() fails and let the 
mount continue? IMO, the mlog line can't help much.

Otherwise, this patch looks good to me.


Thanks,
Changwei


> +	}
> +
>   	status = ocfs2_journal_toggle_dirty(osb, 1, replayed);
>   	if (status < 0) {
>   		mlog_errno(status);
>