linux-ext4 - Ext4 corruption with VM images as 3 > drop

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Date:   Wed, 18 Mar 2020 09:17:51 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org, "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Ext4 corruption with VM images as 3 > drop_caches

Hi,

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.

-aneesh