Re: [uml-devel] Integer overflows in new AIO ubd driver

[Gerd S. <in...@ge...>]

Am Montag, den 27.03.2006, 10:38 -0500 schrieb Jeff Dike:
> On Sun, Mar 26, 2006 at 08:49:25PM +0200, Gerd Stolpmann wrote:
> > I recently tried to benchmark the new AIO-based ubd driver (including
> > O_DIRECT), and ran into serious problems with filesystems > 4GB. I think
> > I found the problem; two overflows in ubd_kern.c (see patch).
> 
> The first bit looks reasonable.  I would change start to an unsigned
> long long instead of casting, though.
> 
> > I also experienced (hard) lockups when doing lots of I/O. But this seems
> > to be unrelated to this problem (but who knows).
> 
> What was your workload?

I used iozone in various ways. The simplest workload leading to problems
was:

- Write a 5GB file
- Write it again
- Read it back
- Read it back

This benchmark ran fine the first time I started it. When I started it
again, UML locked up in the middle. This is reproducible.

Gerd
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