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Subject: Re: Ext4 corruption with VM images as 3 > drop_caches
To:     Jan Kara <jack@suse.cz>
Cc:     linux-ext4@vger.kernel.org, "Theodore Y. Ts'o" <tytso@mit.edu>,
        Ritesh Harjani <riteshh@linux.ibm.com>
References: <87pndagw7s.fsf@linux.ibm.com>
 <20200319163613.GA3339@quack2.suse.cz>
From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Date:   Fri, 20 Mar 2020 09:37:27 +0530
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On 3/19/20 10:06 PM, Jan Kara wrote:
> Hi!
> 
> On Wed 18-03-20 09:17:51, Aneesh Kumar K.V wrote:
>> With new vm install I am finding corruption with the vm image if I
>> follow up the install with echo 3 > /proc/sys/vm/drop_caches
>>
>> The file system reports below error.
>>
>> Begin: Running /scripts/local-bottom ... done.
>> Begin: Running /scripts/init-bottom ...
>> [    4.916017] EXT4-fs error (device vda2): ext4_lookup:1700: inode #787185: comm sh: iget: checksum invalid
>> done.
>> [    5.244312] EXT4-fs error (device vda2): ext4_lookup:1700: inode #917954: comm init: iget: checksum invalid
>> [    5.257246] EXT4-fs error (device vda2): ext4_lookup:1700: inode #917954: comm init: iget: checksum invalid
>> /sbin/init: error while loading shared libraries: libc.so.6: cannot open shared object file: Error 74
>> [    5.271207] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
>>
>> And debugfs reports
>>
>> debugfs:  stat <917954>
>> Inode: 917954   Type: bad type    Mode:  0000   Flags: 0x0
>> Generation: 0    Version: 0x00000000
>> User:     0   Group:     0   Size: 0
>> File ACL: 0
>> Links: 0   Blockcount: 0
>> Fragment:  Address: 0    Number: 0    Size: 0
>> ctime: 0x00000000 -- Wed Dec 31 18:00:00 1969
>> atime: 0x00000000 -- Wed Dec 31 18:00:00 1969
>> mtime: 0x00000000 -- Wed Dec 31 18:00:00 1969
>> Size of extra inode fields: 0
>> Inode checksum: 0x00000000
>> BLOCKS:
>> debugfs:
>>
>> Bisecting this finds
>> Commit 244adf6426ee31a83f397b700d964cff12a247d3("ext4: make
>> dioread_nolock the default") as bad. If I revert the same on top of linus
>> upstream(fb33c6510d5595144d585aa194d377cf74d31911) I don't hit the
>> corrupttion anymore.
> 
> Thanks for report and the bisection! Is this guest or host kernel that you
> were bisecting? I presume host but I want to make sure.
> 

host kernel. W.r.t guest kernel, it is not dependent on guest kernel 
version. I was able to recreate with different guest kernel versions 
(ubuntu 5.3.0-42-generic kernel and also with upstream)

-aneesh