[Bug 214927] New: re-mount read-write (mount -oremount,rw) of read-only filesystem rejected with EROFS, but block device is nor read-only

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https://bugzilla.kernel.org/show_bug.cgi?id=214927

            Bug ID: 214927
           Summary: re-mount read-write (mount -oremount,rw) of read-only
                    filesystem rejected with EROFS, but block device is
                    nor read-only
           Product: File System
           Version: 2.5
    Kernel Version: 4.12.14-122.91-default (SLES12 SP5)
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext3
          Assignee: fs_ext3@kernel-bugs.osdl.org
          Reporter: Ulrich.Windl@rz.uni-regensburg.de
        Regression: No

I think there's a kernel or filesystem bug related to ext3:
We run a SLES12 SP5 Xen PVM that gets its system disk from a sparse file
located on a SLES15 SP2 Xen host using OCFS2 (the host is a node in a pacemaker
cluster).

The OCFS2 filesystem became full or almost full, and thus the ext3
filesystem(s) experienced write errors, remounting to read-only.
So far, so good, but:
The errors behavior of ext 3 was set to "continue", so I wonder why it had been
set to read-only at all.
Next, after having extended the OCFS2 filesystem size, any remount-attempt
fails with:

mount: /: cannot remount /dev/... read-write, is write-protected.

I strace-d the mount command and the mount syscall is returning EROFS
(Read-only filesystem).
However in the VM configuration on the host the disk is marked read-write, the
disk in the VM is flagged read-write, also the VG, LVs, etc. I checked the
/sys/block/*/ro, too: It's all "0".

I also did an fsck (which succeeded), but still after that the error is the
same.
Interestingly I noticed that after a *failed* remount attempt, the filesystem
(that is mounted read-only) got the error flag being set again.

The only conclusion I have is that there is at least one kernel bug regarding
the read-only status of the block device.

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