Repeatable panic from 'camcontrol devlist'

I'm running a -CURRENT kernel built about a week ago, and on
'camcontrol devlist' I get the following repeatable panic:

#10 0xc063b1d5 in panic (fmt=0xc084458e "vmapbuf")
    at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/kern/kern_shutdown.c:534
#11 0xc0684d4e in vmapbuf (bp=0xc4659400) at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/kern/vfs_bio.c:3729
#12 0xc0444c81 in cam_periph_mapmem (ccb=0x0, mapinfo=0xcda8f8a8)
    at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/cam/cam_periph.c:652
#13 0xc0446eaa in xptioctl (dev=0x0, cmd=3255201792, addr=0xcda8f8a8 "", flag=3, td=0xc2204390)
    at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/cam/cam_xpt.c:1132
#14 0xc06009ec in spec_ioctl (ap=0xcda8fb7c) at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/fs/specfs/spec_vnops.c:351
#15 0xc0600108 in spec_vnoperate (ap=0x0) at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/fs/specfs/spec_vnops.c:122
#16 0xc069e0e1 in vn_ioctl (fp=0xc2117b6c, com=3261076738, data=0xc2067000, active_cred=0xc211c980, td=0xc2204390)
    at vnode_if.h:503
#17 0xc0660e35 in ioctl (td=0xc2204390, uap=0xcda8fd10) at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/sys/file.h:261

It doesn't happen on another machine running a kernel built
yesterday.  If anybody can confirm that this problem has been fixed,
I'll leave it; otherwise any pointers would be of use.  FWIW, it dies
here:

(kgdb) f 11
#11 0xc0684d4e in vmapbuf (bp=0xc4659400) at /src/FreeBSD/5-CURRENT-WANTADILLA/src/sys/kern/vfs_bio.c:3729
3729                    panic("vmapbuf: mapped more than MAXPHYS");
(kgdb) l
3724                    if (m == NULL)
3725                            goto retry;
3726                    bp->b_pages[pidx] = m;
3727            }
3728            if (pidx > btoc(MAXPHYS))
3729                    panic("vmapbuf: mapped more than MAXPHYS");
3730            pmap_qenter((vm_offset_t)bp->b_saveaddr, bp->b_pages, pidx);
3731
3732            kva = bp->b_saveaddr;
3733            bp->b_npages = pidx;
(kgdb) p pidx
$2 = 0xcda8f8a8

Greg
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