Re: JFYI: ext4 bug triggerable by kvm

Anthony Liguori
2010-08-16T14:43:16Z

On 08/16/2010 09:00 AM, Michael Tokarev wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=16165
>
> When a (raw) guest image is placed on an ext4 filesystem,
> it is possible to get data corruption, now due to ext4
> bug, not kvm bug.
>

Yeah, there appears to be a few O_DIRECT related issues with ext4.
AFAIK, a preallocated raw image should be safe though which is probably
the only time you should use O_DIRECT.

> Also, ext4 is _very_ slow on O_SYNC writes (which is
> used in kvm with default cache).
>

Yeah, we probably need to switch to sync_file_range() to avoid the
journal commit on every write.

Regards,

Anthony Liguori

> JFYI.
>
> /mjt
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