Here is the info I've grabbed from a Woodcrest Xeon machine that deadlocked under our stress test this morning. Oddly, even though it is built as an SMP kernel, it's only running one CPU of the four available cores - is that a result of having to set hint.apic.0.disabled="1" to avoid an interrupt problem? Anyway, our stress test has a lot of process churn (fork/exec) that has already exposed one race in procfs for which Kostik Belousov just commited a fix. What follows is a by-hand copy of what appears to be most relevant. I have a (large - 4GB) core dump that I can refer back to if necessary. Thanks in advance for any help! Guy db> show allpcpu Current CPU: 0 cpuid = 0 curthread = 0xffffff0x12f46b720: pid 17 "swi6: Giant taskq" curpcb = 0xffffffffb395ad10 fpcurthread = none idlethread = 0xffffff012f46a720: pid 10 "idle: cpu0" spin locks held: db> show alllocks Process 87741 (perform_ca) thread 0xffffff00acd90260 (100350) exclusive sx allproc r = 0 (0xffffffffff8070dd60) locked @ kern/kern_exit.c:674 exclusive sx proctree r = 0 (0xffffffffff8070dde0) locked @ kern/kern_exit.c:602 Process 83677 (ph) thread 0xffffff0065f15000 (100076) exclusive sx user map r = 0 (0xffffff00af53d6d0) locked @ vm/vm_map.c:3074 Process 813 (sendmail) thread 0xffffff012efa3000 (1000036) exclusive sx sysctl lock r = 0 (0xffffffff8070e580) locked @ kern/kern_sysctl.c:1375 Process 17 (swi6: Giant taskq) thread 0xffffff012f46b720 (1000012) exclusive sleep mutex Giant r = 0 (0xffffffff8070d300) locked @ kern/kern_intr.c:681 db> show sleepchain 87741 thread 100350 (pid 87741, perform_ca) is on a run queue db> show sleepchain 83677 thread 100299 (pid 83677, ph) sleeping on 0xffffff0065f15720 "umtx" db> show sleepchain 813 thread 1000036 (pid 813, sendmail) blocked on lk "allproc" EXCL (count 0) db> where 87741 Tracing pid 87741 tid 100350 td 0xffffff00acd90260 sched_switch() at sched_switch+0x13a mi_switch() at mi_switch_0x1d2 maybe_preempt() at maybe_preempt+0x132 sched_add() at sched_add+x17e intr_event_schedule_thread() at intr_event_schedule_thread+0xbc atpic_handle_intr() at atpic_handle_intr+0x5b Xatpic_intr10() at Xatpic_intr10+0x6b --- interrupt, rip = 0xffffffff80325b88, rsp = 0xffffffffb63469d0, rbp = 0xffffffffb646a00 --- _mtx_lock_flags() at _mtx_lock_flags+0x8 _sx_asset() at _sx_assert+0x8f _sx_xunlock() at _sx_xunlock+0x33 kern_wait() at kern_wait+0x597 wait4() at wait4+0x38 syscall() at syscall+0x4d1 Xfast_syscall() at Xfast_syscall+0xa8 --- syscall (7, FreeBSD ELF64, wait4), rip = 0x4114fc, rsp = 0x7fffffffb9c8, rbp = 0x156c4 --- db> where 83677 Tracing pid 83677 tid 100299 td 0xffffff0065f15720 sched_switch() at sched_switch+0x13a mi_switch() at mi_switch+0x1d2 sleepq_switch() at sleepq_switch+0xc2 sleepq_wait_sig() at sleepq_wait_sig+0x28 msleep() at msleep+0x2d8 _do_lock() at _do_lock+0x598 _umtx_op() at _umtx_op+0x4d1 syscall() at syscall+0x4d1 Xfast_syscall() at Xfast_syscall+0xa8 --- syscall (454, FreeBSD ELF64, _umtx_op), rip = 0x800da0e3c, rsp = 0x7ffffedf63c8, rbp = 0xfa0180 --- db> where 813 Tracing pid 813 tid 1000036 td 0xffffff012efa3000 sched_switch() at sched_switch+0x13a mi_switch() at mi_switch+0x1d2 sleepq_switch() at sleepq_switch+0xc2 sleepq_wait() at sleepq_wait+0x40 cv_wait() at cv_wait+0x16f _sx_slock() at _sx_slock+0xb8 pfind() at pfind+0x22 sysctl_kern_proc_args() at sysctl_kern_proc_args+0x2f sysctl_root() at sysctl_root+0xa0 userland_sysctl() at userland_sysctl+0x11c __sysctl() at __sysctl+0xcd syscall() at syscall+0x4d1 Xfast_syscall() at Xfast_syscall+0xa8 --- syscall (202, FreeBSD ELF64, __sysctl), rip = 0x800d16afc, rsp = 0x7fffffffb048, rbp = 0x483d47 --- db> where 17 Tracing pid 17 tid 100012 td 0xffffff012f46b720 kdb_enter() at kdb_enter+0x2f scgetc() at scgetc+0x43e sckbdevent() at sckbdevent+0x83 kbdmux_intr() at kbdmux_intr+0x4d kbdmux_kbd_intr() at kbdmux_kbd_intr+0x20 taskqueue_run() at taskqueue_run+0x135 ithread_loop() at ithread_loop+0x14c fork_exit() at fork_exit+0xbb fork_trampoline() at fork_trampoline+0xe --- trap 0, rip = 0, rsp = 0xfffffffffb395ad00, rbp = 0 --- db> allt .... db> where 87429 Tracing command perform_ca pid 87429 tid 100145 0xffffff00b5861000 sched_switch() at sched_switch+0x13a mi_switch() at mi_switch+0x1d2 sleepq_switch() at sleepq_switch+0xc2 sleepq_wait() at sleepq_wait+0x40 cv_wait() at cv_wait+0x16f _sx_unlock() at _sx_unlock+0x71 _vm_map_lock() at _vm_map_lock+0x3e vm_map_remove() at vm_map_remove+0x2e pipe_free_kmem() at pipe_free_kmem+0x72 pipeclose() at pipeclose+0x272 pipe_close() at pipe_close+0x31 fdrop_locked() at fdrop_locked+0xa1 closef() at closef+0x35f close() at close+0x172 syscall() at syscall+0x4d1 Xfast_syscall() at Xfast_syscall+0xa8 --- syscall (6, FreeBSD ELF64, close), rip = 0x42425c, rsp = 0x7fffffffb9a8, rbp = 0 --- db> show sleepchain 819 thread 100055 (pid 819, sendmail) blocked on sx "sysctl lock" XLOCK thread 100036 (pid 813, sendmail) blocked on lk "allproc" EXCL (count 0) db> where 819 Tracing pid 819 tid 100055 td 0xffffff012efa3980 sched_switch() at sched_switch+0x13a mi_switch() at mi_switch+0x1d2 sleepq_switch() at sleepq_switch+0xc2 sleepq_wait() at sleepq_wait+0x40 cv_wait() at cv_wait+0x16f _sx_xlock() at _sx_xlock+0x71 userland_sysctl() at userland_sysctl+0xf5 __sysctl() at __sysctl+0xcd syscall() at syscall+0x4d1 Xfast_syscall() at Xfast_syscall+0xa8 --- syscall (202, FreeBSD ELF64, __sysctl), rip = 0x800d16afc, rsp = 0x7fffffffcde8, rbp = 0x3 --- db>