clang compiled kernel panic when mounting zfs root on i386

[sig6247]

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>