Access to tape drive caused following backtrace

Hi,

I was just doung a tar -tf /dev/sa0 when I got (hand transcribed):

uma_zalloc_arg: zone "32" with the following non-sleepable locks held:
exclusive sleep mutex ahc_lock r = 0 (0xc3cb2eb0) locked _at_ /usr/src/sys/cam/cam_
periph.h:182
KDB: stack backtrace:
db_trace_self_wrapper(c01afca0,df502850,c076fcfd,c0a20063,df502864,...) at db_tr
ace_self_wrapper+0x26
kdb_backtrace(c0a20063,df502864,4,1,0,...) at kdb_backtrace+0x29
witness_warn(5,0,c0a3a76f,c0a408e1,c3b76000,...) at witness_warn+0x41cd
uma_zalloc_arg(c1472b40,0,102,2,c3ef6400,...) at uma_zalloc_arg+0x34
malloc(1c,c0a564e0,102,df502900,c09d8343,...) at malloc+0xd2
sagetparams(c3ef6484,c3ef6480,c3ef6488,df50299f,c3ef6485,...) at sagetparams+0x4
2c
samount(c3e81a80,14c,c09d88343,b6,6,...) at samount+0x6df
saopen(c3de8900,1,2000,c4080600,c0a56760,...) at sa_open+0x124
giant_open(c3de8900,1,2000,c4080600,c3f08200,...) at giant_open+0x4f
devfs_open(df502a8c,c4080600,df502b80,df502b1c,...) at devfs_open+0x230
VOP_OPEN_APV(c0ac19e0,df502a8c,df502a78,246,c424a000,...) at VOP_OPEN_APV+0xa5
vn_open_cred(df502b80,df502c78,0,c4233180,c4064e58,...) at vn_open_cred+0x44b
vn_open(df502b80,df502c78,0,c4064e58,246,...) at vn_open+0x33
kern_open(c4080600,df502cfc,c,c,c0ac4918,...) at kern_open+0xc3
open(c4080600,df502cfc,c,c,c0ac4918,...) at open+0x30
syscall(df502d38) at syscall+0x288
Xint0x80_syscall() at Xint0x80_syscall+0x20
--- syscall (5, FreeBSD ELF32, open), eip = 0x28194a7b, esp = 0xbfbfe9fc, ebp =
0xbfbfea88 ---

The machine did not panic, seemed to still be responsive. Maybe the
problem has been fixed since the CURRENT I am running, but I thought I
should post this anyway.

Cheers, Alex J Burke.