# trace -e waitid,wait4

   0.557 ( 0.557 ms): bash/27335 wait4(upid: -1, stat_addr: 0x7ffd02f449f0) = 27336
   1.250 ( 0.685 ms): bash/27335 wait4(upid: -1, stat_addr: 0x7ffd02f449f0) = 27337
   1.312 ( 0.002 ms): bash/27335 wait4(upid: -1, stat_addr: 0x7ffd02f44690, options: NOHANG) = -1 ECHILD No child processes
   1.550 ( 0.015 ms): bash/3856 wait4(upid: -1, stat_addr: 0x7ffd02f44990, options: NOHANG|UNTRACED|CONTINUED) = 27335
   1.552 ( 0.001 ms): bash/3856 wait4(upid: -1, stat_addr: 0x7ffd02f44990, options: NOHANG|UNTRACED|CONTINUED) = 0
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-i5vlo5n5jv0amt8bkyicmdxh@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>