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: <5DFCC3F5.7040702@huawei.com>
Date:   Fri, 20 Dec 2019 20:52:05 +0800
From:   Jiangyiwen <jiangyiwen@...wei.com>
To:     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>,
        "chge@...ux.alibaba.com" <chge@...ux.alibaba.com>
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 2019/12/20 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() 
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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