Probably this bug happened to me before, yet I had no ideas how to file it. When drawing windows or doing updates like popping on Everything sometimes enlightenment hangs and remains hanged on 'uwait' signal.

After update to 0.19.13,2 things go worse. I also have problems with Firefox (https://bugzilla.mozilla.org/show_bug.cgi?id=1153650) and when Firefox crashed the window was zoomed out and then halfway through the zoom everything hanged. This time enlightenment is eating 100% CPU on 'usem'.

ktrace:

  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0
  7003 Eanimator-timer CALL  select(0x16,0x7fffdfdfce80,0x7fffdfdfce00,0x7fffdfdfcd80,0x7fffdfdfcd70)
  7003 Eanimator-timer RET   select 0

core (obtained with kill -5):

(gdb) bt full
#0  0x0000000804d34a08 in _umtx_op () from /lib/libc.so.7
No symbol table info available.
#1  0x0000000804d20fca in sem_timedwait () from /lib/libc.so.7
No symbol table info available.
#2  0x000000080176d768 in eina_thread_queue_wait () from /usr/local/lib/libeina.so.1
No symbol table info available.
#3  0x0000000801f226ef in evas_common_scale_sample_init () from /usr/local/lib/libevas.so.1
No symbol table info available.
#4  0x000000080176d2e2 in eina_thread_create () from /usr/local/lib/libeina.so.1
No symbol table info available.
#5  0x00000008019a4855 in pthread_create () from /lib/libthr.so.3
No symbol table info available.
#6  0x0000000000000000 in ?? ()
No symbol table info available.

uname -a:
FreeBSD limbo.b1t.name 10.2-STABLE FreeBSD 10.2-STABLE #143 r290942M: Mon Nov 16 21:35:12 EET 2015     arcade@limbo.b1t.name:/usr/obj/usr/src/sys/MINIMAL  amd64

Graphics: ATI, though previously I faced similar problems with nvidia.

PS: Happened twice already, would be easy to reproduce I think.