linux-ext4 - Question about JBD2 transactions

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Message-ID: <loom.20160321T031409-338@post.gmane.org>
Date:	Mon, 21 Mar 2016 02:23:55 +0000 (UTC)
From:	Abraham Choi <north.choi@...il.com>
To:	linux-ext4@...r.kernel.org
Subject: Question about JBD2 transactions

Hi all,

Frist of all, thank you for Ext4's developer.

I have encounterd a crash problem of ext4 file system on Kernel 3.18.20 
with mounting 
rw,seclabel,nosuid,nodev,relatime,discard,noauto_da_alloc,data=ordered 0 0.
[   22.361511] EXT4-fs error (device sda8): ext4_mb_generate_buddy:757: 
group 0, block bitmap and bg descriptor inconsistent: 21208 vs 21219 free 
clusters
I think, the reason is that recovered transactions has not recovered over 
39809 during booting.
Booting N-2
	[   16.416979] (jbd2_journal_recover, 279): JBD2: recovery, exit 
status 0, recovered transactions 39665 to 39728
	Last commit_sequence=39796
Booting N-1
	[   16.626582] (jbd2_journal_recover, 279): JBD2: recovery, exit 
status 0, recovered transactions 39730 to 39797
	Last commit_sequence=39866
Booting N
	[   14.118542] (jbd2_journal_recover, 279): JBD2: recovery, exit 
status 0, recovered transactions 39799 to 39809
	
The root casue will be explained the more detail in the follwing.
Jounral Blocks
... <Descriptor block #39808> <Data blocks> <Commit block #39808> 
<All zero block> <Descriptor block #39809> <Data blocks> <Commit block 
#39809> ... 
I'm wondering that journal has all zero data, only 1 block.
How it can be possible?
Any tips or help would be appreciated.

Regards,
Abraham Choi

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