LOR: "ata state lock" and "user map"

NOTE: CURRENT was run under qemu emulation, CDROM was emulated from iso
image on HDD.

Got this LOR today with CURRENT built 3 days ago while trying to execute
a linux program located on a CD. Several days ago trying to do the same
on 5.4-RELEASE (without any debug options in kernel) on real hardware
caused a hardlock.

System:
6.0-CURRENT i386
debug.mpsafevm=1

LOR message had this information:
1st 0xc0eb44e8 ATA state lock ata-all.c:297
2nd 0xc0c1f344 user map vm_map.c:2997

Sources:
ata-all.c 1.252
/vm_map.c 1.366

Interesting part of stack trace (not sure how useful it is):
#18 0x0000000c in ?? ()
#19 0x00000002 in ?? ()
#20 0xc0455a15 in ata_pio_read (request=0xc107b0c8, length=2048)
    at cpufunc.h:229
#21 0xc045646c in ata_end_transaction (request=0xc107b0c8)
    at /usr/src/sys/dev/ata/ata-lowlevel.c:393
#22 0xc0447659 in ata_interrupt (data=0xc0eb4400)
    at /usr/src/sys/dev/ata/ata-all.c:323
#23 0xc04b5360 in ithread_loop (arg=0xc0eb9600)
    at /usr/src/sys/kern/kern_intr.c:546
#24 0xc04b46fd in fork_exit (callout=0xc04b51bc <ithread_loop>,
    arg=0xc0eb9600, frame=0xc7b41d38) at /usr/src/sys/kern/kern_fork.c:789
#25 0xc05df18c in fork_trampoline () at
/usr/src/sys/i386/i386/exception.s:208

Please let me know what additional information I can provide.

-- 
Andriy Gapon