TAKE - Fix migration of pagebuf I/O completion threads with the O(1) scheduler

[Christoph Hellwig <hch@xxxxxxxxxxxxxxxxxxxxxx>]

Fix from Andrea Arcangeli to not lockup the machine when XFS is combined with 
the
O(1) scheduler patch.  I had to add some ugly #ifdef magic to detect that case.


Date:  Thu Sep 12 02:54:15 PDT 2002
Workarea:  dhcp212.munich.sgi.com:/home/hch/repo/ptools/linux-2.4-xfs

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/slinx/2.4.x-xfs


Modid:  2.4.x-xfs:slinx:127220a
linux/fs/xfs/pagebuf/page_buf.c - 1.58
        - Fix migration of pagebuf I/O completion threads with the O(1) 
scheduler