Configure the 2.4.21-pre3 kernel with IDE and Highmem and when DMA is
attempted you get a BUG from asm-i386/pci.h line 155 called from
drives/ide/ide-dma.c line 282.
From the looks of it, the IDE driver has not been highmem enabled, but
does get a high-mem device queue.
This is easily reproduced on a dual proc P3 with 2 Gigs of ram.
Ross