Hi,
some of our customers (Proxmox VE) are seeing issues with file
corruptions when accessing contents located on CephFS via the in-kernel
Ceph client [0,1], we managed to reproduce this regression on kernels up
to the latest 6.11-rc6.
Accessing the same content on the CephFS using the FUSE client or the
in-kernel ceph client with older kernels (Ubuntu kernel on v6.5) does
not show file corruptions.
Unfortunately the corruption is hard to reproduce, seemingly only a
small subset of files is affected. However, once a file is affected, the
issue is persistent and can easily be reproduced.
Bisection with the reproducer points to this commit:
"92b6cc5d: netfs: Add iov_iters to (sub)requests to describe various
buffers"
Description of the issue:
A file was copied from local filesystem to cephfs via:
```
cp /tmp/proxmox-backup-server_3.2-1.iso
/mnt/pve/cephfs/proxmox-backup-server_3.2-1.iso
```
* sha256sum on local
filesystem:`1d19698e8f7e769cf0a0dcc7ba0018ef5416c5ec495d5e61313f9c84a4237607
/tmp/proxmox-backup-server_3.2-1.iso`
* sha256sum on cephfs with kernel up to above commit:
`1d19698e8f7e769cf0a0dcc7ba0018ef5416c5ec495d5e61313f9c84a4237607
/mnt/pve/cephfs/proxmox-backup-server_3.2-1.iso`
* sha256sum on cephfs with kernel after above commit:
`89ad3620bf7b1e0913b534516cfbe48580efbaec944b79951e2c14e5e551f736
/mnt/pve/cephfs/proxmox-backup-server_3.2-1.iso`
* removing and/or recopying the file does not change the issue, the
corrupt checksum remains the same.
* accessing the same file from different clients results in the same
output: the one with above patch applied do show the incorrect checksum,
ones without the patch show the correct checksum.
* the issue persists even across reboot of the ceph cluster and/or clients.
* the file is indeed corrupt after reading, as verified by a `cmp -b`.
Interestingly, the first 4M contain the correct data, the following 4M
are read as all zeros, which differs from the original data.
* the issue is related to the readahead size: mounting the cephfs with a
`rasize=0` makes the issue disappear, same is true for sizes up to 128k
(please note that the ranges as initially reported on the mailing list
[3] are not correct for rasize [0..128k] the file is not corrupted).
In the bugtracker issue [4] I attached a ftrace with "*ceph*" as filter
while performing a read on the latest kernel 6.11-rc6 while performing
```
dd if=/mnt/pve/cephfs/proxmox-backup-server_3.2-1.iso of=/tmp/test.out
bs=8M count=1
```
the relevant part shown by task `dd-26192`.
Please let me know if I can provide further information or debug outputs
in order to narrow down the issue.
[0] https://forum.proxmox.com/threads/78340/post-676129
[1] https://forum.proxmox.com/threads/149249/
[2] https://forum.proxmox.com/threads/151291/
[3]
https://lore.kernel.org/lkml/db686d0c-2f27-47c8-8c14-26969433b13b@xxxxxxxxxxx/
[4] https://bugzilla.kernel.org/show_bug.cgi?id=219237
#regzbot introduced: 92b6cc5d
Regards,
Christian Ebner
