Re: [2.6.30 and later] file corruption on ext3 filesystem.

From: Tetsuo Handa
Date: Fri Jan 08 2010 - 08:15:31 EST


Dave Chinner wrote:
> On Fri, Jan 08, 2010 at 11:54:24AM +0900, Tetsuo Handa wrote:
> > I'm experiencing file corruption problem.
> > Can somebody reproduce below result?
> >
> > My environment:
> > VMware Workstation 6.5.3 with 2CPUs / 512MB RAM.
> > ext3 filesystem ( /dev/sda1 ) mounted on / .
> >
> > 2.6.33-rc3 ( )
> > ( )
> > ( )
> >
> >
> > So far, I haven't succeeded to reproduce this problem for 2.6.29 and earlier.
> > Maybe this problem exists in only 2.6.30 and later.
> Isn't that when the default mount options changed from data=ordered to
> data=writeback?
Ah, indeed. 2.6.31 mounts data=writeback whereas 2.6.29 mounts data=ordered.

In my Ubuntu 9.10 environment, it is using data=writeback mode, and therefore
I got garbage data taken from other deleted files.

> You didn't fsync() it, so there is no reason for the kernel
> to have ever written it to disk. Therefore the result after powerfail
> is completely undefined - you data may be there, it may not...

I didn't call fsync(). Thus, I don't mind if the data I wrote is not written
to disk.

However, I feel something is very wrong because the file got data which I
didn't write. The file gets data from deleted files. Imagine that unprivileged
user can get the content of /etc/shadow if power failure occurred when the user
was running ./a.out .

The file should not get data from deleted files, but I can read the data from
deleted files by "cat /testfile". I feel something is very wrong.

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