[lttng-dev] lttng create freezes sometimes

[Sébastien Barthélémy]

Hello Mathieu,

2012/1/25 Mathieu Desnoyers <compudj at krystal.dyndns.org>:
> Please try with commit:
>
> commit 5a532b6873b6d619381c0188b91e48106e639808
> Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> Date:   Wed Jan 25 09:39:28 2012 -0500
>
>    Fix lttng sessiond spawn wait race
>
>    If the child is scheduled before the parent, using "pause()" in the
>    parent could be executed after the signal has been handled: that's
>    entirely racy. Use a proper signal handler and flag to handle this
>    racelessly.
>
>    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
>
> Let me know how it works,

It works, thanks! I can run the following without any failure:

$ for i in {1..100}; do killall lttng-sessiond; sleep 1; echo "$i";
lttng create;done

However, if I remove the sleep, I get 7 other failures.
Likely race conditions between the kill and the subsequent start,
which is an unlikely use pattern.

Here they are anyway:

17
==> like 60

31
Spawning a session daemon
chmod: No such file or directory
Error: Session daemon died (exit status 0)

33
==> like 89

60
Spawning a session daemon
rm: cannot remove `/home/nao/.lttng': Directory not empty
Session auto-20120126-122706 created.
Traces will be written in /home/nao/lttng-traces/auto-20120126-122706

75
Spawning a session daemon
LTTng Trace Control 2.0-pre18

usage: lttng [options] <command>

Options:
  -h, --help             Show this help
  -g, --group NAME       Unix tracing group name. (default: tracing)
  -v, --verbose          Verbose mode
  -q, --quiet            Quiet mode
  -n, --no-sessiond      Don't spawn a session daemon
      --sessiond-path    Session daemon full path
      --list-options     Simple listing of lttng options
      --list-commands    Simple listing of lttng commands

Commands:
    add-context     Add context to event or/and channel
    calibrate       Quantify LTTng overhead
    create          Create tracing session
    destroy         Teardown tracing session
    enable-channel  Enable tracing channel
    enable-event    Enable tracing event
    disable-channel Disable tracing channel
    disable-event   Disable tracing event
    list            List possible tracing options
    set-session     Set current session name
    start           Start tracing
    stop            Stop tracing
    version         Show version information

Please see the lttng(1) man page for full documentation.
See http://lttng.org for updates, bug reports and news.


85
Spawning a session daemon
rm: cannot remove `/home/nao/.lttng': Is a directory
Session auto-20120126-122708 created.
Traces will be written in /home/nao/lttng-traces/auto-20120126-122708

89
epoll_wait: Bad file descriptor
Spawning a session daemon
Session auto-20120126-122709 created.
Traces will be written in /home/nao/lttng-traces/auto-20120126-122709

I also got some

$ killall lttng-sessiond ; lttng create
Spawning a session daemon
bind: No such file or directory
Error: Session daemon died (exit status 0)

Regards,

-- Sébastien