On 2019/1/5 上午7:04, Nazar Mokrynskyi wrote:
> 04.01.19 03:32, Qu Wenruo пише:
>> Please provide the dump of the following command:
>>
>> # btrfs ins dump-tree -t extent | grep 3114475520 -C 20
> root@nazarpc-Standard-PC-Q35-ICH9-2009:~# btrfs ins dump-tree -t extent 
> /dev/vdc | grep 3114475520 -C 20
[snip]
>     item 152 key (3114475520 EXTENT_ITEM 4096) itemoff 10193 itemsize 24
>         refs 2 gen 1701147 flags DATA
>     item 153 key (3114475520 EXTENT_ITEM 36864) itemoff 10169 itemsize 24
>         refs 1 gen 1712966 flags DATA

Two extent backref for one bytenr, this is definitely a problem.

>     item 154 key (3114475520 SHARED_DATA_REF 311408951296) itemoff 10165 
> itemsize 4
>         shared data backref count 1
>     item 155 key (3114475520 SHARED_DATA_REF 342561947648) itemoff 10161 
> itemsize 4
>         shared data backref count 1
>     item 156 key (3114475520 SHARED_DATA_REF 348547874816) itemoff 10157 
> itemsize 4
>         shared data backref count 1

And total of 3 refs, 1 or 2 of them are the cause.

I'd say either it's caused by kernel bug or corrupted space cache/block
group item.

Please don't mount the fs RW, and copy your data out.

In fact I don't have any idea how this happened, no clue to fix either.

Thanks,
Qu

> 
> Actually, I removed Docker's snapshots after making image, but most others 
> are not there anymore.
> 
<snip>
> I'm using qcow2 with snapshots, so I can do multiple experiments with image 
> at the same time if necessary. Also started `btrfs check --mode=lowmem`, will 
> report once it finishes.



> 
> 

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