linux-kernel - Re: [Ocfs2-devel] [PATCH v3] ocfs2: call journal flush to mark journal as empty after journal recovery when mount

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Message-ID: <05cf7457-31f2-0698-14ae-21a9e7b659cb@linux.alibaba.com>
Date:   Fri, 20 Dec 2019 09:11:50 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     piaojun <piaojun@...wei.com>, Kai Li <li.kai4@....com>,
        mark@...heh.com, jlbec@...lplan.org, chge@...ux.alibaba.com
Cc:     linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v3] ocfs2: call journal flush to mark
 journal as empty after journal recovery when mount



On 19/12/19 22:15, piaojun wrote:
> 
> 
> On 2019/12/17 10:01, 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.
>>
>> The following steps describe this procedure in detail.
>> 1. mount and touch some files
>> 2. these transactions are committed to journal area but not checkpointed
>> 3. emergency restart
>> 4. mount again and its journals are replayed
>> 5. journal super block's first s_start is 1, but its s_seq is not updated
>> 6. touch a new file and its trans is committed but not checkpointed
>> 7. emergency restart again
>> 8. mount and journal is dirty, but trans committed in 6 will not be
>> replayed.
>>
>> This exception happens easily 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 super block will be updated after recovery like what this patch
>> does.
>>
>> ocfs2_recover_node->ocfs2_replay_journal.
>>
>> 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@....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..68ba354cf361 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) {
>> +		jbd2_journal_lock_updates(journal->j_journal);
>> +		status = jbd2_journal_flush(journal->j_journal);
> 
> What if jbd2_journal_flush gets failed? The 's_sequence' and 's_start'
> won't be reset, and I wonder if the problem still remains.
> 

Yes, but we don't want this to fail the mount process, instead we just log
an error and system administrator should know the result.

Thanks,
Joseph