On Thu, 2017-01-26 at 18:22 -0700, Jens Axboe wrote:

What's your boot device? I've been booting this on a variety of setups,
no problems observed. It's booting my laptop, and on SCSI and SATA as
well. What is your root drive? What is the queue depth of it?
Controller?

The boot device in my test setup is a SATA hard disk:

# cat /proc/cmdline  
BOOT_IMAGE=/boot/vmlinuz-4.10.0-rc5-dbg+ root=UUID=60a4b064-b3ef-4d28-96d3-3c13ecbec43e resume=/dev/sda2 showopts
# ls -l /dev/disk/by-uuid/60a4b064-b3ef-4d28-96d3-3c13ecbec43e
lrwxrwxrwx 1 root root 10 Jan 27 08:43 /dev/disk/by-uuid/60a4b064-b3ef-4d28-96d3-3c13ecbec43e -> ../../sda1
# cat /sys/block/sda/queue/nr_requests  
31
# lsscsi | grep sda
[0:0:0:0]    disk    ATA      ST1000NM0033-9ZM GA67  /dev/sda
# hdparm -i /dev/sda

/dev/sda:
 Model=ST1000NM0033-9ZM173, FwRev=GA67, SerialNo=Z1W2HM75
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=0
 BuffType=unknown, BuffSize=unknown, MaxMultSect=16, MultSect=off
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4  
 DMA modes:  mdma0 mdma1 mdma2  
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6  
 AdvancedPM=no WriteCache=disabled
 Drive conforms to: Unspecified:  ATA/ATAPI-4,5,6,7

 * signifies the current active mode

Bart.