I just tried a top of tree i386 kernel under KVM, and found that it 
fails to boot with a hang during initialization, right after:

console [netcon0] enabled 

netconsole: network logging started 

Uniform Multi-Platform E-IDE driver 

ide-floppy driver 1.00 

Driver 'sd' needs updating - please use bus_type methods 

scsi0 : ata_piix 

scsi1 : ata_piix 

ata1: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc000 irq 14 

ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc008 irq 15 

ata1.00: ATA-7: QEMU HARDDISK, 0.9.1, max UDMA/100 

ata1.00: 16777216 sectors, multi 16: LBA48 

ata1.00: configured for MWDMA2 

ata2.00: ATAPI: QEMU DVD-ROM, 0.9.1, max UDMA/100 

ata2.00: configured for MWDMA2 

scsi 0:0:0:0: Direct-Access     ATA      QEMU HARDDISK    0.9. PQ: 0 
ANSI: 5

Bisection fingered the following commit:

7404ad3b6d04efbd918e9e2e776bf560fbedf47d is first bad commit 

commit 7404ad3b6d04efbd918e9e2e776bf560fbedf47d 

Author: James Bottomley <James.Bottomley@HansenPartnership.com> 

Date:   Sun Aug 31 10:41:52 2008 -0500 


     [SCSI] sd: use generic helper to print capacities in both binary and SI

     Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

:040000 040000 98fc7ae95211b8d16e2e8ca46997be660ad9ba93 
2d35d0a2b6232411b840a9ccf6a52b946172566e M      drivers

However, simply reverting this commit caused a panic on boot (not 
entirely surprising.)

Config attached (applied with yes '' | make oldconfig).

	-hpa