[lttng-dev] lttng create freezes sometimes

[Sébastien Barthélémy]

Hello,

2012/1/27 David Goulet <dgoulet at efficios.com>:
> On 12-01-26 08:19 AM, Sébastien Barthélémy wrote:
>> 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.
>
> Hmmmm... yes looks like a race. I can't get any errors on my side... I even bump
> it up to 1000 and still nothing...
>
> It seems your system is quite a challenge for us! :)

It is a 500MHz AMD Geode processor. I'm pretty sure your workstation has more
horsepower ;)


> This is most irregular since chmod() is *always* done after a mkdir, a socket
> creation or shm open....

I imagine the scheduler might not agree with our definition of after ;).

Wouldn't the following be possible?

lttng-sessiond1 is running. .lttng exists
lttng-sessiond2 creates .lttng (as it already exists, this is a no-op)
lttng-sessiond1 get killed. It deletes .lttng
lttng-sessiond2 tries to chmod .lttng, which does not exist anymore

>> 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
>
> Again here, we use "rm -rf" for now ... how can you get this kind of error
> message with "-rf" ....?

I dunno...

> Looking at the rest, you have a bind() error, Bad file descriptor and more "no
> such file or dir...". Is your open files limit is very low? Maybe there is a
> couple of place where we don't handle well the maximum open files error.

The limit is 1024. Quite usual no?