panic: ruleset 0 already running

Up-to-date 6.0 SMP machine.  Devfs mounts are coming and going, but
there should be no transient devices (which are known to cause panics
when racing with umount), and I am not using any explicit rulesets.

Tracing pid 46736 tid 100131 td 0xc6b1aa80
kdb_enter(c07400fa,1,c07397b9,ee25ab60,c6b1aa80) at kdb_enter+0x30
panic(c07397b9,0,c6740d00,3,c7352980) at panic+0x13e
devfs_ruleset_applyde(c66ee160,c7352980,ee25abc8,c0515fdf,c9345100) at devfs_ruleset_applyde+0x2a
devfs_rules_apply(c9345100,c7352980,0,c6b1aa80,c0739625) at devfs_rules_apply+0x37
devfs_populate(c9345100,1,0,c6b1aa80,c0739625) at devfs_populate+0x2f3
devfs_readdir(ee25ac88,0,0,cada7e70,ee25acd4) at devfs_readdir+0x96
VOP_READDIR_APV(c07751a0,ee25ac88,c6b1aa80,c074824c,e4d) at VOP_READDIR_APV+0x9d
getdirentries(c6b1aa80,ee25ad04,10,421,4) at getdirentries+0x171
syscall(806003b,806003b,bfbf003b,8056200,1) at syscall+0x295
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (196, FreeBSD ELF32, getdirentries), eip = 0x280d020f, esp = 0xbfbfe7ac, ebp = 0xbfbfe7d8 ---

I am not able to dump core on this machine, so I will leave it in DDB
for now.

Kris