ZFS Deadlock: 'Directory of Death'

[Ori Bernstein]

I've got a fun issue: There's a directory of death on my desktop running ZFS.
When installing ports, I Any program that tries to touch a directory in
/usr/ports hangs, deadlocked in the VFS cache lookup:

	$ sudo procstat -kk 94688
	PID    TID COMM             TDNAME           KSTACK                       
	94688 102697 fuser            -                mi_switch+0xe1 sleepq_wait+0x3a sleeplk+0x15d __lockmgr_args+0x91a vop_stdlock+0x3c VOP_LOCK1_APV+0xab _vn_lock+0x43 vget+0x73 cache_lookup+0x5d5 vfs_cache_lookup+0xac VOP_LOOKUP_APV+0xa1 lookup+0x5a1 namei+0x4d4 kern_statat_vnhook+0xae sys_stat+0x2d amd64_syscall+0x40f Xfast_syscall+0xfb 


The process that seems to have triggered this was a port install of NPM, which seems to have
deadlocked while renaming some files:

	$ ps a 93931
	93931 15- D      0:11.87 npm (node)

	$ sudo procstat -kk 93931
	PID    TID COMM             TDNAME           KSTACK                       
	93931 101449 node             -                mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d umtxq_sleep+0x125 do_sem_wait+0x4db __umtx_op_sem_wait+0x73 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 101977 node             -                mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d kern_kevent_fp+0x399 kern_kevent+0x9f sys_kevent+0x12a amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102252 node             V8 WorkerThread  mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d umtxq_sleep+0x125 do_sem_wait+0x4db __umtx_op_sem_wait+0x73 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102258 node             V8 WorkerThread  mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d umtxq_sleep+0x125 do_sem_wait+0x4db __umtx_op_sem_wait+0x73 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102262 node             V8 WorkerThread  mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d umtxq_sleep+0x125 do_sem_wait+0x4db __umtx_op_sem_wait+0x73 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102266 node             V8 WorkerThread  mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d umtxq_sleep+0x125 do_sem_wait+0x4db __umtx_op_sem_wait+0x73 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102279 node             -                mi_switch+0xe1 sleepq_catch_signals+0xab sleepq_wait_sig+0xf _sleep+0x27d umtxq_sleep+0x125 do_wait+0x387 __umtx_op_wait_uint_private+0x83 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102285 node             -                mi_switch+0xe1 sleepq_wait+0x3a sleeplk+0x15d __lockmgr_args+0xca0 vop_stdlock+0x3c VOP_LOCK1_APV+0xab _vn_lock+0x43 vputx+0x21f zfs_rename_unlock+0x3e zfs_freebsd_rename+0xe39 VOP_RENAME_APV+0xab kern_renameat+0x4a6 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102287 node             -                mi_switch+0xe1 sleepq_wait+0x3a sleeplk+0x15d __lockmgr_args+0x91a vop_stdlock+0x3c VOP_LOCK1_APV+0xab _vn_lock+0x43 zfs_lookup+0x45d zfs_freebsd_lookup+0x6d VOP_CACHEDLOOKUP_APV+0xa1 vfs_cache_lookup+0xd6 VOP_LOOKUP_APV+0xa1 lookup+0x5a1 namei+0x4d4 kern_renameat+0x1b7 amd64_syscall+0x40f Xfast_syscall+0xfb 
	93931 102294 node             -                mi_switch+0xe1 sleepq_wait+0x3a sleeplk+0x15d __lockmgr_args+0x91a vop_stdlock+0x3c VOP_LOCK1_APV+0xab _vn_lock+0x43 vget+0x73 cache_lookup+0x5d5 vfs_cache_lookup+0xac VOP_LOOKUP_APV+0xa1 lookup+0x5a1 namei+0x4d4 kern_renameat+0x1b7 amd64_syscall+0x40f Xfast_syscall+0xfb 

The specific directory that is causing this issue is:

	/usr/ports/www/npm/work/stage/usr/local/lib/node_modules/npm/node_modules/npmlog/node_modules/gauge

Right now I'm running on a stock FreeBSD 10.3 release.

	FreeBSD oneeye 10.3-RELEASE-p4 FreeBSD 10.3-RELEASE-p4 #0: Sat May 28 12:23:44 UTC 2016     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64

I'm going to guess that this deadlock will go away if I reboot this box, but
I haven't rebooted yet. Since this isn't really impacting anything important
that I'm doing, I can keep it up for a bit if someone wants me to gather some
extra information to track down the root cause.

-- 
    Ori Bernstein