clang compiled kernel panic when mounting zfs root on i386

Hi,

Just checked out r243529, this only happens when the kernel is compiled
by clang, and only on i386, either recompiling the kernel with gcc or
booting from a UFS root works fine. Is it a known problem?

Thanks,

----------------------------------------------------------------------
WARNING: WITNESS option enabled, expect reduced performance.
Trying to mount root from zfs:zroot []...

Fatal double fault:
eip = 0xc0adc37d
esp = 0xc86bffc8
ebp = 0xc86c003c
cpuid = 1; apic id = 01
panic: double fault
cpuid = 1
KDB: enter: panic
[ thread pid 1 tid 100002 ]
Stopped at      kdb_enter+0x3d: movl    $0,kdb_why
db> bt
Tracing pid 1 tid 100002 td 0xc89efbc0
kdb_enter(c1064aa4,c1064aa4,c10b806f,c139e3b8,f5eacada,...) at kdb_enter+0x3d
panic(c10b806f,1,1,1,c86c003c,...) at panic+0x14b
dblfault_handler() at dblfault_handler+0xab
--- trap 0x17, eip = 0xc0adc37d, esp = 0xc86bffc8, ebp = 0xc86c003c ---
witness_checkorder(c1fd7508,9,c109df18,7fa,0,...) at witness_checkorder+0x37d
__mtx_lock_flags(c1fd7518,0,c109df18,7fa,c135d918,...) at __mtx_lock_flags+0x87
uma_zalloc_arg(c1fd66c0,0,1,4d3,c86c0110,...) at uma_zalloc_arg+0x605
vm_map_insert(c1fd508c,c13dfc10,bb1f000,0,cba1e000,...) at vm_map_insert+0x499
kmem_back(c1fd508c,cba1e000,1000,3,c86c01d4,...) at kmem_back+0x76
kmem_malloc(c1fd508c,1000,3) at kmem_malloc+0x250
page_alloc(c1fd1d80,1000,c86c020b,3,c1fd1d80,...) at page_alloc+0x27
keg_alloc_slab(103,4,c109df18,870,cb99ef6c,...) at keg_alloc_slab+0xc3
keg_fetch_slab(103,c1fd1d80,cb99ef6c,c1fc8230,c86c02c0,...) at keg_fetch_slab+0xe2
zone_fetch_slab(c1fd1d80,c1fd0480,103,826,0,...) at zone_fetch_slab+0x43
uma_zalloc_arg(c1fd1d80,0,102,3,2,...) at uma_zalloc_arg+0x3f2
malloc(4c,c1686100,102,c86c0388,c173d09a,...) at malloc+0xe9
zfs_kmem_alloc(4c,102,cb618820,c89efbc0,cb618820,...) at zfs_kmem_alloc+0x20
vdev_mirror_io_start(cb8218a0,10,cb8218a0,1,0,...) at vdev_mirror_io_start+0x14a
zio_vdev_io_start(cb8218a0,c89efbc0,0,cb8218a0,c86c0600,...) at zio_vdev_io_start+0x228
zio_execute(cb8218a0,cb618000,cba1b640,cb900000,400,...) at zio_execute+0x106
spa_load_verify_cb(cb618000,0,cba1b640,cb884b40,c86c0600,...) at spa_load_verify_cb+0x89
traverse_visitbp(cb884b40,cba1b640,c86c0600,c86c0ba0,0,...) at traverse_visitbp+0x29f
traverse_dnode(cb884b40,0,0,8b,0,...) at traverse_dnode+0x92
traverse_visitbp(cb884bb8,cba07200,c86c0890,cb884bf4,c16ce7e0,...) at traverse_visitbp+0xe47
traverse_visitbp(cb884bf4,cb9bf840,c86c0968,c86c0ba0,0,...) at traverse_visitbp+0xf32
traverse_dnode(cb884bf4,0,0,0,0,...) at traverse_dnode+0x92
traverse_visitbp(0,cb618398,c86c0b50,2,cb9f1c78,...) at traverse_visitbp+0x96d
traverse_impl(0,0,cb618398,3e1,0,...) at traverse_impl+0x268
traverse_pool(cb618000,3e1,0,d,c1727830,...) at traverse_pool+0x79
spa_load(0,1,c86c0ec4,1e,0,...) at spa_load+0x1dde
spa_load(0,0,c13d8c94,1,3,...) at spa_load+0x11a5
spa_load_best(0,ffffffff,ffffffff,1,c0adc395,...) at spa_load_best+0x71
spa_open_common(c17e0e1e,0,0,c86c1190,c16f5a1c,...) at spa_open_common+0x11a
spa_open(c86c1078,c86c1074,c17e0e1e,c135d918,c1fd7798,...) at spa_open+0x27
dsl_dir_open_spa(0,cb770030,c17e11b1,c86c11f8,c86c11f4,...) at dsl_dir_open_spa+0x6c
dsl_dataset_hold(cb770030,cb613800,c86c1240,cb613800,cb613800,...) at dsl_dataset_hold+0x3a
dsl_dataset_own(cb770030,0,cb613800,c86c1240,c1684e30,...) at dsl_dataset_own+0x21
dmu_objset_own(cb770030,2,1,cb613800,c86c1290,...) at dmu_objset_own+0x2a
zfsvfs_create(cb770030,c86c13ac,c17ee05d,681,0,...) at zfsvfs_create+0x4c
zfs_mount(cb78ed20,c17f411c,c9ff4600,c89cae80,0,...) at zfs_mount+0x42c
vfs_donmount(c89efbc0,4000,0,c86c1790,cb6c0800,...) at vfs_donmount+0xc6d
kernel_mount(cb7700b0,4000,0,0,1,...) at kernel_mount+0x6b
parse_mount(cb7700e0,c1194498,0,1,0,...) at parse_mount+0x606
vfs_mountroot(c13d95b0,4,c105c042,2bb,0,...) at vfs_mountroot+0x6cf
start_init(0,c86c1d08,c105e94c,3db,0,...) at start_init+0x6a
fork_exit(c0a42090,0,c86c1d08) at fork_exit+0x7f
fork_trampoline() at fork_trampoline+0x8
--- trap 0, eip = 0, esp = 0xc86c1d40, ebp = 0 ---
db>