Mild filesystem corruption on ext4 (no journal)

Alan Jenkins
2009-06-05T10:48:28Z

Hi,

I run ext4 without a journal on my cheap netbook with a 4 gig SSD. I
suspect "without a journal" is significant, I don't think I'm doing
anything else strange.

When I upgrade libc from 2.7 (debian stable) to 2.9 (debian unstable),
the locale breaks every reboot, and I have to repair it by running
locale-gen. This happened now when I only upgraded libc, in order to
play with signalfd(). It also happened before, when I upgraded the
entire machine to debian unstable (which I later reverted).

The problem is that /usr/lib/locale/locale-archive gets corrupted when I
reboot. The exact corruption differs with each reboot (i.e. the md5sum
differs). Last time, the first ~70K was overwritten with data from
xorg.log and my web browsing history. I have copies of the original and
corrupted state which I can send, the full file is 1.3 megs, but I can
limit it to the first 70K, since that's all that was corrupted.

To try and rule out a faulty userspace program, I marked the file as
read-only (chmod a-w) and immutable (chattr +i). After a reboot, the
file was still read-only and immutable, yet it still became corrupted.

Also, I ran md5sum in the shutdown scripts, after mounting the root
filesystem read-only (which is also preceeded by a sync in a different
script). This showed that the file did not appear corrupted at this
point. (Though maybe it was ok in page-cache, but corrupted on-disk).

The locale-archive file is read by the libc locale routines using
mmap(). The mapping is read only and is not modified. It seems likely
that some process has it mapped when the kernel shuts down.

I tried reproducing this by writting a minimal daemon which maps a copy
of the locale-archive file, and starting it just before the filesystem
is remounted read-only. It didn't work though; this copy of the
locale-archive file remained uncorrupted.

I forced a fsck on boot, and the filesystem was reported to be clean. I
am currently running with e2fsprogs v1.41.6 (from debian unstable), and
a custom-built kernel, 2.6.30-rc7.

Thanks in advance!
Alan