Re: [PATCH 00/23] per device dirty throttling -v8

[Andrew Morton]

On Sat, 04 Aug 2007 21:16:35 +0200 Florian Weimer <fw@xxxxxxxxxxxxx> wrote:

> * Andrew Morton:
> 
> > The easy preventive is to mount with data=writeback.  Maybe that should
> > have been the default.
> 
> The documentation I could find suggests that this may lead to a
> security weakness (old data in blocks of a file that was grown just
> before the crash leaks to a different user).

yup.  This problem also exists in ext2, reiserfs (unless using
ordered-mode), JFS, others.

>  XFS overwrites that data
> with zeros upon reboot, which tends to irritate users when it happens.

yup.

> >From this point of view, data=ordered doesn't seem too bad.

If your computer is used by multiple users who don't trust each other,
sure.  That covers, what?  About 2% of machines?

I was using data=writeback for a while on my most-thrashed disk.  The
results were a bit disappointing - not much difference.  ext2 is a lot
quicker.

(I don't use anything which is fsync-happy, btw).  (I used to have a patch
which sysctl-tunably turned fsync, msync, fdatasync into "return 0" for use
on the laptop but I seem to have lost it)



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