Here are stack traces of all the frozen processes (with a few newlines inserted manually):
Crash version 8.1_STABLE, image version 8.1_STABLE. Output from a running system is unreliable. crash> trace/t 0t16306 trace: pid 16306 lid 1 at 0xffff8001578daa20 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_root() at nfs_root+0x2b VFS_ROOT() at VFS_ROOT+0x35 lookup_once() at lookup_once+0x250 namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 fd_nameiat.isra.2() at fd_nameiat.isra.2+0x54 do_sys_statat() at do_sys_statat+0x77 sys___stat50() at sys___stat50+0x28 syscall() at syscall+0x1ec --- syscall (number 439) --- 787fc74f98ca: crash> trace/t 0t16685 trace: pid 16685 lid 1 at 0xffff80015791aae0 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_root() at nfs_root+0x2b VFS_ROOT() at VFS_ROOT+0x35 lookup_once() at lookup_once+0x250 namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 chdir_lookup() at chdir_lookup+0x70 sys_chdir() at sys_chdir+0x26 syscall() at syscall+0x1ec --- syscall (number 12) --- 758c3b8820ca: crash> trace/t 0t19979 trace: pid 19979 lid 1 at 0xffff80013ed7ea20 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_root() at nfs_root+0x2b VFS_ROOT() at VFS_ROOT+0x35 lookup_once() at lookup_once+0x250 namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 fd_nameiat.isra.2() at fd_nameiat.isra.2+0x54 do_sys_statat() at do_sys_statat+0x77 sys___lstat50() at sys___lstat50+0x25 syscall() at syscall+0x1ec --- syscall (number 441) --- 7c0a9c4a1a7a: crash> trace/t 0t25025 trace: pid 25025 lid 1 at 0xffff8001576628a0 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_lookup() at nfs_lookup+0xf84 VOP_LOOKUP() at VOP_LOOKUP+0x85 lookup_once() at lookup_once+0x18d namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 fd_nameiat.isra.2() at fd_nameiat.isra.2+0x54 do_sys_statat() at do_sys_statat+0x77 sys___stat50() at sys___stat50+0x28 syscall() at syscall+0x1ec --- syscall (number 439) --- 6fd53d4f98ca: crash> trace/t 0t28321 trace: pid 28321 lid 1 at 0xffff80013f8768a0 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_lookup() at nfs_lookup+0xf84 VOP_LOOKUP() at VOP_LOOKUP+0x85 lookup_once() at lookup_once+0x18d namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 fd_nameiat.isra.2() at fd_nameiat.isra.2+0x54 do_sys_statat() at do_sys_statat+0x77 sys___stat50() at sys___stat50+0x28 syscall() at syscall+0x1ec --- syscall (number 439) --- 7656ab6f98ca: crash> trace/t 0t18618 trace: pid 18618 lid 1 at 0xffff80013f9b2a20 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_root() at nfs_root+0x2b VFS_ROOT() at VFS_ROOT+0x35 lookup_once() at lookup_once+0x250 namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 fd_nameiat.isra.2() at fd_nameiat.isra.2+0x54 do_sys_statat() at do_sys_statat+0x77 sys___lstat50() at sys___lstat50+0x25 syscall() at syscall+0x1ec --- syscall (number 441) --- 7cbc7f0a1a7a: crash> trace/t 0t22881 trace: pid 22881 lid 1 at 0xffff80013eef6a20 sleepq_block() at sleepq_block+0x97 turnstile_block() at turnstile_block+0x24f rw_vector_enter() at rw_vector_enter+0x120 genfs_lock() at genfs_lock+0x47 VOP_LOCK() at VOP_LOCK+0x80 vn_lock() at vn_lock+0x11 nfs_root() at nfs_root+0x2b VFS_ROOT() at VFS_ROOT+0x35 lookup_once() at lookup_once+0x250 namei_tryemulroot.constprop.9() at namei_tryemulroot.constprop.9+0x3b1 namei() at namei+0x43 fd_nameiat.isra.2() at fd_nameiat.isra.2+0x54 do_sys_statat() at do_sys_statat+0x77 sys___stat50() at sys___stat50+0x28 syscall() at syscall+0x1ec --- syscall (number 439) --- 792b4e4f98ca: