Re: [BUG REPORT] ext4: “errors=remount-ro” has become “errors=shutdown”?

Baokun Li
2025-01-04T02:41:32Z

Hi Ted,

On 2025/1/3 23:54, Theodore Ts'o wrote:
> On Fri, Jan 03, 2025 at 10:35:17AM -0500, Theodore Ts'o wrote:
>> I don't see how setting the shutdown flag causes reads to fail. That
>> was true in an early version of the ext4 patch which implemented
>> shutdown support, but one of the XFS developers (I don't remember if
>> it was Dave or Cristoph) objected because XFS did not cause the
>> read_pages function to fail. Are you seeing this with an upstream
>> kernel, or with a patched kernel? The upstream kernel does *not* have
>> the check in ext4_readpages() or ext4_read_folio() (post folio
>> conversion).
> OK, that's weird. Testing on 6.13-rc4, I don't see the problem simulating an ext4 error:
>
> root@kvm-xfstests:~# mke2fs -t ext4 -Fq /dev/vdc
> /dev/vdc contains a ext4 file system
> last mounted on /vdc on Fri Jan 3 10:38:21 2025
> root@kvm-xfstests:~# mount -t ext4 -o errors=continue /dev/vdc /vdc
We are discussing "errors=remount-ro," as the title states, not the
continue mode. The key code leading to the behavior change is as follows,
therefore the continue mode is not affected.

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -657,7 +657,7 @@ static void ext4_handle_error(struct super_block
*sb, bool force_ro, int error,
WARN_ON_ONCE(1);

if (!continue_fs && !sb_rdonly(sb)) {
-               ext4_set_mount_flag(sb, EXT4_MF_FS_ABORTED);
+               set_bit(EXT4_FLAGS_SHUTDOWN, &EXT4_SB(sb)->s_ext4_flags);
if (journal)
jbd2_journal_abort(journal, -EIO);
}

See the end for problem reproduction.

> [ 24.780982] EXT4-fs (vdc): mounted filesystem f8595206-fe57-486c-80dd-48b03d41ebdb r/w with ordered data mode. Quota mode: none.
> root@kvm-xfstests:~# cp /etc/motd /vdc/motd
> root@kvm-xfstests:~# echo testing > /sys/fs/ext4/vdc/trigger_fs_error
> [ 42.943141] EXT4-fs error (device vdc): trigger_test_error:129: comm bash: testing
> root@kvm-xfstests:~# cat /vdc/motd
>
> The programs included with the Debian GNU/Linux system are free software;
> the exact distribution terms for each program are described in the
> individual files in /usr/share/doc/*/copyright.
>
> Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
> permitted by applicable law.
> root@kvm-xfstests:~#
>
>
> HOWEVER, testing with shutdown ioctl, both ext4 and xfs are failing with EIO:
Yes, this is as expected.
> root@kvm-xfstests:~# mount /dev/vdc /vdc
> [ 7.969168] XFS (vdc): Mounting V5 Filesystem 7834ea96-eab0-46c5-9b18-c8f054fa9cf4
> [ 7.978539] XFS (vdc): Ending clean mount
> root@kvm-xfstests:~# cp /etc/motd /vdc
> root@kvm-xfstests:~# /root/xfstests/src/godown -v /vdc
> Opening "/vdc"
> Calling XFS_IOC_GOINGDOWN
> [ 29.354609] XFS (vdc): User initiated shutdown received.
> [ 29.356123] XFS (vdc): Log I/O Error (0x6) detected at xfs_fs_goingdown+0x55/0xb0 (fs/xfs/xfs_fsops.c:452). Shutting down filesystem.
> [ 29.357092] XFS (vdc): Please unmount the filesystem and rectify the problem(s)
> root@kvm-xfstests:~# cat /vdc/motd
> cat: /vdc/motd: Input/output error
> root@kvm-xfstests:~#
>
> So I take back what I said earlier, but I am a bit confused why it
> worked after simulating an file system error using "echo testing >
> /sys/fs/ext4/vdc/trigger_fs_error".
>
It's because "errors=remount-ro" wasn't used when mounting...

Here's a replication:

root@kvm-xfstests:~# mount -o errors=remount-ro /dev/vdc /mnt/test
[  115.731007] EXT4-fs (vdc): mounted filesystem
0838f08f-c04e-440c-a9a5-417677efb03e r/w with ordered data mode. Quota
mode: none.
root@kvm-xfstests:~# echo test > /mnt/test/file
root@kvm-xfstests:~# cat /mnt/test/file
test
root@kvm-xfstests:~# echo 1 > /sys/fs/ext4/vdc/trigger_fs_error
[  131.537649] EXT4-fs error (device vdc): trigger_test_error:129: comm
bash: 1
[  131.538226] Aborting journal on device vdc-8.
[  131.538844] EXT4-fs (vdc): Remounting filesystem read-only
root@kvm-xfstests:~# cat /mnt/test/file
cat: /mnt/test/file: Input/output error
root@kvm-xfstests:~# uname -a
Linux kvm-xfstests 6.13.0-rc4-xfstests-g6cfe3548f8f5-dirty #284 SMP
PREEMPT_DYNAMIC Fri Dec 27 10:39:02 CST 2024 x86_64 GNU/Linux

Regards,
Baokun