This was observed in two server nodes.

#0  0xfed9a0b7 in _lwp_kill () from /lib/libc.so.1
(gdb) bt
#0  0xfed9a0b7 in _lwp_kill () from /lib/libc.so.1
#1  0xfed95814 in thr_kill () from /lib/libc.so.1
#2  0xfed41df3 in raise () from /lib/libc.so.1
#3  0xfee57065 in gf_print_trace (signum=11) at common-utils.c:439
#4  0xfed9742f in __sighndlr () from /lib/libc.so.1
#5  0xfed8d141 in call_user_handler () from /lib/libc.so.1
#6  <signal handler called>
#7  0xfee5b13f in inode_ref (inode=0x0) at inode.c:391
#8  0xfe3ca2b3 in server_stub_resume (stub=0xa256808, op_ret=-1, op_errno=2, inode=0x0, parent=0x0) at server-protocol.c:2584
#9  0xfe3d8977 in __do_path_resolve_cbk (frame=0xa160ec8, cookie=0xa1915b0, this=0x80b2f28, op_ret=-1, op_errno=2, 
    inode=0xa8230f8, stbuf=0xfe07de70, dict=0x0) at server-dentry.c:236
#10 0xfee52254 in default_lookup_cbk (frame=0xa1915b0, cookie=0xa2634a8, this=0x80b2e20, op_ret=-1, op_errno=2, 
    inode=0xa8230f8, buf=0xfe07de70, dict=0x0) at defaults.c:46
#11 0xfec337ab in iot_lookup_cbk (frame=0xa2634a8, cookie=0xa19a358, this=0x80b2d50, op_ret=-1, op_errno=2, inode=0xa8230f8, 
    buf=0xfe07de70, xattr=0x0) at io-threads.c:222
#12 0xfee52254 in default_lookup_cbk (frame=0xa19a358, cookie=0xa172c18, this=0x80b2cb8, op_ret=-1, op_errno=2, 
    inode=0xa8230f8, buf=0xfe07de70, dict=0x0) at defaults.c:46
#13 0xfec732a8 in posix_lookup (frame=0xa172c18, this=0x80b1fd8, loc=0xa25c9d8, xattr_req=0x0) at posix.c:308
#14 0xfee5234b in default_lookup (frame=0xa19a358, this=0x80b2cb8, loc=0xa25c9d8, xattr_req=0x0) at defaults.c:61
#15 0xfec338a2 in iot_lookup_wrapper (frame=0xa2634a8, this=0x80b2d50, loc=0xa25c9d8, xattr_req=0x0) at io-threads.c:231
#16 0xfee63a49 in call_resume_wind (stub=0xa25c9c0) at call-stub.c:2633
#17 0xfee66612 in call_resume (stub=0xa25c9c0) at call-stub.c:4169
#18 0xfec39180 in iot_worker_unordered (arg=0x80b31d0) at io-threads.c:2058
#19 0xfed97045 in _thr_setup () from /lib/libc.so.1
#20 0xfed97330 in L3_doit () from /lib/libc.so.1
#21 0xfeca1a00 in ?? ()
#22 0x00000000 in ?? ()
(gdb)