reproducible xfs/vmap oops

[Christoph Hellwig]

On Wed, Feb 04, 2009 at 08:42:45AM +1100, Dave Chinner wrote:
> On Tue, Feb 03, 2009 at 04:04:23PM -0500, Christoph Hellwig wrote:
> > [ 3138.799436] XFS mounting filesystem vde
> > [ 3138.813184] va->va_start = 4290777088, va->va_end = 4096
> > [ 3138.834754] tmp->va_start = 4195352576, tmp->va_end = 4196401152
> > [ 3138.846352] ------------[ cut here ]------------
> > [ 3138.850332] kernel BUG at mm/vmalloc.c:298!
> > [ 3138.850332] invalid opcode: 0000 [#1] SMP 
> > 
> > The first va_end looks suspicious to me..
> 
> That is on i386, Christoph? If so, I'd suspect a 32 bit overflow
> as 4290777088 = 0xFFC01000 and va_start/va_end are unsigned longs.
> If we tried to map exactly 4MB the with va_start at 0xFFC01000 we'd
> end up with va_end at 0x100001000 which would wrap to 0x1000 = 4096.

Yeah, this is 32-bit x86.  Exactly my thoughts, but just to make sure
the overflow is in vmap and not in XFS I'm running with your checking
patch included now.