Possible regression after NFS eof page pollution fix (ext4 checksum errors)

[Mark Bloch <mbloch@nvidia.com>]

Hi Trond,

We’ve recently started seeing filesystem issues in our internal
regression runs, and we were able to bisect the problem down to
the following commit:

commit b1817b18ff20e69f5accdccefaf78bf5454bede2
Author: Trond Myklebust <trond.myklebust@hammerspace.com>
Date:   Thu Sep 4 18:46:16 2025 -0400

    NFS: Protect against 'eof page pollution'

    This commit fixes the failing xfstest 'generic/363'.

    When the user mmaps() an area that extends beyond the end of file, and
    proceeds to write data into the folio that straddles that eof, we're
    required to discard that folio data if the user calls some function that
    extends the file length.

    Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>


After this change, we intermittently see EXT4 checksum-related errors during boot.
A representative dmesg excerpt is below:

 [ 1908.365537] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #263414: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1908.375449] EXT4-fs error (device vda2): __ext4_find_entry:1624: inode #263414: comm updatedb: checksumming directory block 0
 [ 1908.382985] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #263414: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1908.389289] EXT4-fs error (device vda2): __ext4_find_entry:1624: inode #263414: comm updatedb: checksumming directory block 0
 [ 1909.598811] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #423753: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1909.604308] EXT4-fs error (device vda2): htree_dirblock_to_tree:1051: inode #423753: comm updatedb: Directory block failed checksum
 [ 1909.958470] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #423759: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1909.963825] EXT4-fs error (device vda2): htree_dirblock_to_tree:1051: inode #423759: comm updatedb: Directory block failed checksum
 [ 1909.985956] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #303617: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1909.991371] EXT4-fs error (device vda2): __ext4_find_entry:1624: inode #303617: comm updatedb: checksumming directory block 0
 [ 1910.156415] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #423761: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1910.161959] EXT4-fs error (device vda2): htree_dirblock_to_tree:1051: inode #423761: comm updatedb: Directory block failed checksum
 [ 1910.171364] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #423735: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1910.177292] EXT4-fs error (device vda2): htree_dirblock_to_tree:1051: inode #423735: comm updatedb: Directory block failed checksum
 [ 1910.267721] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #423744: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1910.281838] EXT4-fs error (device vda2): htree_dirblock_to_tree:1051: inode #423744: comm updatedb: Directory block failed checksum
 [ 1910.476906] EXT4-fs warning (device vda2): ext4_dirblock_csum_verify:375: inode #423751: comm updatedb: No space for directory leaf checksum. Please run e2fsck -D.
 [ 1910.482403] EXT4-fs error (device vda2): htree_dirblock_to_tree:1051: inode #423751: comm updatedb: Directory block failed checksum

The issue has so far only been observed in tests that use a nested VM setup.
It does not reproduce deterministically, roughly half of the nested
VM boots trigger the problem.

Would you mind taking a look or pointing us in the right direction?
Please let us know if additional information, testing,
or instrumentation would be helpful.

Thanks,
Mark