[lvm-devel] lvresize in test mode sends BLKDISCARD to SSD block devices, this will result in the file system corruption

[Gang He]

Hello Zdenek,

Thank for your quick response.
I opened a bug in redhat bugzilla for this issue.
The bug link is https://bugzilla.redhat.com/show_bug.cgi?id=1595500

Thanks
Gang


>>> On 6/22/2018 at  9:34 pm, in message
<87afa0a1-c256-60a9-2603-57e7be9a00d3 at redhat.com>, Zdenek Kabelac
<zkabelac at redhat.com> wrote:
> Dne 22.6.2018 v 11:31 Gang He napsal(a):
>> Hello List,
>> 
>> I found a bug for lvresize command, this issue can be reproduced by 
> lvm2-2.02.178 code base.
>> The reproduce steps are as below,
> 
> 
> Hi
> 
> Good catch - yep - it seem in this case  ioctl operation are flowing to 
> device 
> even in test mode.
> 
> Please create BZ for lvm2 on this issue.
> 
> 
> Zdenek
> 
> 
>> 1) create a LV on a SSD based partition, then format this LV with ext4 file 
> system, and mount this LV.
>> e.g.
>> linux-cy2k:/ # lsblk
>> ...
>> sdc                               8:32   0  37.3G  0 disk
>> ├─sdc1                            8:33   0     2G  0 part [SWAP]
>> ├─sdc2                            8:34   0  14.7G  0 part
>> │ └─cluster--vg1-test--lv       254:20   0    14G  0 lvm  /mnt/ext4  <<= this 
> LV
>> └─sdc3                            8:35   0  20.6G  0 part
>> 
>> 2) enable issue discards to a logical volumes's underlying physical volume 
> via edit "/etc/lvm/lvm.conf" file.
>> e.g.
>> linux-cy2k:/ # vi /etc/lvm/lvm.conf
>> set "issue_discards = 1"
>> 
>> 3) run lvresize command in test mode.
>> e.g.
>> inux-cy2k:/ # lvresize -v -n -L -10GB /dev/cluster-vg1/test-lv --test
>> 
>> 4) unmount this LV, then mount this LV again.
>> You will probably encounter the file system on this LV is corrupted.
>> e.g.
>> linux-cy2k:~ # mount /dev/cluster-vg1/test-lv /mnt/ext4/
>> mount: wrong fs type, bad option, bad superblock on 
> /dev/mapper/cluster--vg1-test--lv,
>>         missing codepage or helper program, or other error
>> 
>>         In some cases useful info is found in syslog - try
>>         dmesg | tail or so.
>> 
>> linux-cy2k:~ # dmesg
>> [3711112.342424] JBD2: no valid journal superblock found
>> [3711112.342429] EXT4-fs (dm-20): error loading journal
>> 
>> To summarize, I think this behavior is a bug and is very dangerous,
>> the command in test mode should not send BLKDISCARD to the underlying block 
> device,
>> the BLKDISCARD command will make the related sectors on the block device be 
> trimmed (lost data).
>> 
>> 
>> Thanks
>> Gang
>>   
>> 
>> --
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>>