[lttng-dev] epoll_wait reboot kernel? [or --disable-epoll causes lttng-sessiond assert]

[David OShea]

Hi all,

Apologies if I'm confusing things, but I think my issue may be related.  Please see below:

> -----Original Message-----
> From: zhenyu.ren [mailto:zhenyu.ren at aliyun.com]
> Sent: Tuesday, 25 February 2014 4:32 PM
> To: Mathieu Desnoyers
> Cc: lttng-dev
> Subject: Re: [lttng-dev] epoll_wait reboot kernel?
> 
> >Which gcc version do you use ?
> $gcc --version
> gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46)

I'm on CentOS 6, so my results ought to be relevant, but the above looks like the default GCC version for EL5, not EL6.  I'm using "gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4)".

[...]
> >  >  I am working on rhel6(2.6.32.220) and ust is working very
> well.But when I
> >  >  use lttng-modules (after "lttng start"),the kernel reboots
> immediately
> >  >  >without any message output to console.

I'm not using the kernel modules here, just lttng-ust.

[...]
> > > I want to use poll instead as epoll in lttng-tools ,I changed
> lttng-tools
> > > configure file to not use epoll(undef HAVE_EPOLL),

Note that 'configure' for lttng-tools has a --disable-epoll option.

> > > but "lttng enable-event
> > > -a -k >"failed :(Do I miss anything?)
> > >#lttng enable-event -a -k
> > >DEBUG1 [17837/18080]: Using run_as_clone (in run_as() at
> runas.c:293)
> > >lttng-sessiond: ht-cleanup.c:92: thread_ht_cleanup: Assertion
> `pollfd ==
> > >ht_cleanup_pipe[0]' failed.

I get similar issues when I run 'lttng enable-event -a -u' (i.e. UST instead of kernel tracing):

DEBUG1 [1292/1297]: Spawning consumerd (in spawn_consumerd() at main.c:2085)
lttng-sessiond: ht-cleanup.c:92: thread_ht_cleanup: Assertion `pollfd == ht_cleanup_pipe[0]' failed.
DEBUG1 [1329/1329]: Using 64-bit UST consumer at: /usr/lib64/lttng/libexec/lttng-consumerd (in spawn_consumerd() at main.c:2161)
Aborted (core dumped)

but only when I configure lttng-tools with --disable-epoll.  If I remove that option at build time, that particular lttng-sessiond assertion failure goes away and UST works fine.

I built with --disable-epoll because I was told that, at least in some previous LTTng version, this was necessary for building on CentOS 5.  I guess I can stop doing that now I'm using CentOS 6, but should this happen or is there a bug here?

> > >PS:.lttng(ust/module/tool) version is 2.3.0 and urcu version is 0.8

I'm using lttng-ust, lttng-tools 2.3.2 and userspace-rcu 0.8.3.

Thanks in advance,
David

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