Date:   Mon, 23 Dec 2019 09:54:44 +0800
From:   Jiangyiwen <jiangyiwen@...wei.com>
To:     Changwei Ge <chge@...ux.alibaba.com>, Likai <li.kai4@....com>,
        piaojun <piaojun@...wei.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        "mark@...heh.com" <mark@...heh.com>,
        "jlbec@...lplan.org" <jlbec@...lplan.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ocfs2-devel@....oracle.com" <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 2019/12/21 15:24, Changwei Ge wrote:
>
>
> On 12/20/19 8:52 PM, Jiangyiwen wrote:
>> On 2019/12/20 17:33, Likai wrote:
>>> On 2019/12/20 17:14, piaojun wrote:
>>>> On 2019/12/20 9:11, Joseph Qi wrote:
>>>>> 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
>>
>> Hi,
>>
>> I wonder that in this step, does the function 
>> jbd2_journal_commit_transaction() return?
>> I understand only jbd2_journal_commit_transaction() return it means 
>> the transaction
>> is committed completely, and the s_seq can be updated in
>> jbd2_journal_commit_transaction()->jbd2_update_log_tail(), so I don't 
>> know how
>> this scenario happened.
>>
>> If emergency restart happens in before jbd2_journal_commit_transaction() 
>
> The trick is that jbd2 kernel thread even doesn't have a chance to to 
> update tail. Assuming that a timepoint sits between *mount completion* 
> and the *first iteration* of committing work that jbd2 thread.
>

Hi Changwei,

So I think if *first iteration* of committing work in jbd2 kernel thread 
is not
completed, and then the transaction should not be considered a valid
transaction.

In addition, since we use ordered mode in jbd2, filesystem only ensure
metadata consistency not data consistency. In above scenario, the filesystem
is still normal without any damage.

Thanks,
Yiwen.

>     -Changwei
>
>> return,
>> I think this transaction shouldn't be a valid transaction.
>>
>> Can you explain where the specific function is executed?
>>
>> Thanks,
>> Yiwen.
>>
>>>>>>> 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 for your reply and I have another question about this issue. 
>>>> IMO
>>>> the second trans is not complete as jbd2 sb has not been updated, 
>>>> so we
>>>> do not need to replay it when mount again.
>>>>
>>>> Jun
>>>>
>>>>
>>> I don't think so. The problem is that jbd2 sb should be updated to mark
>>> a new start after mount rather than whether trans committed later is
>>> complete or not.
>>>
>>> In fact , the trans is complete too as the commit log described.
>>>
>>> Thanks
>>>
>>>
>>> _______________________________________________
>>> Ocfs2-devel mailing list
>>> Ocfs2-devel@....oracle.com
>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>>>
>>> .
>>>
>>
>
> .
>

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