[lustre-devel] LDISKFS-fs error: osd_iget: special inode unallocated, Remounting filesystem read-only

Hello,
 
I have recently started seeing sanity-lfsck failures in tests 18g, 23b, and 23c on Ubuntu 20.04 5.15.0-1051-azure due to the MDT filesystem going readonly preventing either the start of LFSCK or LFSCK operations. In all cases logs on the MDS show the following:
 
Nov 20 20:06:59 e72f0907-59ba-4ffd-9528-2e3ad47050e4-mdsmgs-a0-vm kernel: LDISKFS-fs error (device dm-0): osd_iget:500: inode #195: comm mdt03_003: iget: special inode unallocated Nov 20 20:06:59 e72f0907-59ba-4ffd-9528-2e3ad47050e4-mdsmgs-a0-vm kernel: Aborting journal on device dm-0-8.
Nov 20 20:06:59 e72f0907-59ba-4ffd-9528-2e3ad47050e4-mdsmgs-a0-vm kernel: LustreError: 29024:0:(osd_handler.c:1787:osd_trans_commit_cb()) transaction @0x00000000a2d278af commit error: 2 Nov 20 20:06:59 e72f0907-59ba-4ffd-9528-2e3ad47050e4-mdsmgs-a0-vm kernel: LDISKFS-fs (dm-0): Remounting filesystem read-only
 
LFSCK operations if they start will fail with error code 117 (EFSCORRUPTED):
 
00000020:00000001:8.0:1700166322.660540:0:43212:0:(lu_object.c:908:lu_object_find_at()) Process leaving (rc=18446744073709551499 : -117 : ffffffffffffff8b)
00100000:00000001:8.0:1700166322.660541:0:43212:0:(lfsck_layout.c:3241:lfsck_layout_scan_orphan_one()) Process leaving via out (rc=18446744073709551499 : -117 : 0xffffffffffffff8b)
 
In both cases, the error comes from an ldiskfs_iget operation which passes the LDISKFS_IGET_SPECIAL flag to __ext4_iget. A recent ext4 patch started checking for this flag and will return EFSCORRUPTED if the inode is unallocated (https://lkml.kernel.org/stable/[email protected]/ ).
 
Adding LDISKFS_IGET_SPECIAL always to ldiskfs_iget was done as part of LU-13166 (https://review.whamcloud.com/c/fs/lustre-release/+/37421 ) and feels broad to me in the context of the upstream ext4 change. At the moment I am investigating removing the LDISKFS_IGET_SPECIAL flag from ldiskfs_iget to see how it impacts the LFSCK tests and to determine if a more targeted change can be made to satisfy the intent of LU-13166.
 
Any suggestions or thoughts on how to approach this problem would be greatly appreciated. Additional logs or debugging information can be provided if needed.
 
Thank you and best,
Cyrus Ramavarapu
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