panic: vm_thread_new: kstack allocation failed

Panic running stress2 with libthr on up-to-date 7.0:

panic: vm_thread_new: kstack allocation failed
cpuid = 2
KDB: enter: panic
[thread pid 47238 tid 100136 ]
Stopped at      kdb_enter+0x30: leave
db> wh
Tracing pid 47238 tid 100136 td 0xc6b2a510
kdb_enter(c0720bdf,2,c07375d0,ee266a48,c6b2a510) at kdb_enter+0x30
panic(c07375d0,3000,0,c106c888,0) at panic+0x13f
vm_thread_new(d0b51a20,0,6,ee266b2c,c0676f92) at vm_thread_new+0x7d
thread_init(d0b51a20,1b0,103,103,ee266b2c) at thread_init+0x1a
slab_zalloc(c105c1e0,103,c105c1e0,d0b50fc0,d0b50d80) at slab_zalloc+0x277
uma_zone_slab(c105c1e0,3,c105c1e0,c6b2e69c,ee266b88) at uma_zone_slab+0x15e
uma_zalloc_bucket(c105c1e0,3,c0736a7d,75d,246) at uma_zalloc_bucket+0x18f
uma_zalloc_arg(c105c1e0,0,2,ee266c0c,c053b31d) at uma_zalloc_arg+0x3df
thread_alloc(ee266c10,c053059d,c6b2e704,1,c0721027) at thread_alloc+0x28
create_thread(c6b2a510,0,2807e86f,8058e00,b6b72000) at create_thread+0x6c
thr_new(c6b2a510,ee266d04,8,445,d5362630) at thr_new+0x7f
syscall(c06c003b,3b,3b,0,8058e00) at syscall+0x2ea
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (455, FreeBSD ELF32, thr_new), eip = 0x280cc273, esp = 0xbfbfe13c, ebp = 0xbfbfe1e8 ---
db>

Core available.