[collectd] randomly getting dl_open_worker assertion

[Florian Forster]

Hi Robert,

On Wed, Feb 20, 2013 at 04:21:16PM +0000, Riches Jr, Robert M wrote:
> [2013-02-20 08:01:31] exec plugin: exec_read_one: error = Inconsistency detected by ld.so: dl-open.c: 221: dl_open_worker: Assertion `_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT' failed!

this appears to be an assertion within glibc's implementation of
dlopen(3). [0] It looks like this bug from 2007 could be related: [1]

> There doesn't seem to be any rhyme or reason as to whether I get the
> expected result or the assertion failure.  I've googled for answers
> until my keyboard is wearing out, but nothing has come up that shows
> promise of a solution.

From what you describe, it feels like a concurrency issue. collectd is
using dlopen() to load the plugins, including the exec plugin. This
happens at start-up only; later the mechanism is no longer used, but the
dlopen'ed shared object are never closed, so they are still open when
fork() is called.

> Regarding the behavior when I run the real script that doesn't send
> anything to stderr, […]

I don't think this is related to I/O. It sounds more like a problem
between dlopen() and fork().

How many processors does the machine have on which this problem occurs?
Which libc are you using? Approximately, how often does this happen?

Best regards,
—octo

[0] <http://code.woboq.org/userspace/glibc/elf/dl-open.c.html#259>
[1] <http://www.sourceware.org/bugzilla/show_bug.cgi?id=4578>
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