Pthread_cond_broadcast broken with dlsym?

I am trying to insert calls to pthread_cond_broadcast using the LD_PRELOAD mechanism. My built-in pthread_cond_broadcast function simply calls the original pthread_cond_broadcast. However, for very simple pthread code that calls both pthread_cond_wait and pthread_cond_broadcast, I either end segfault in glibc (for glibc 2.11.1) or the program freezes (for glibc 2.15). Any tips on this going on?

Interposition code (which compiles as a shared library):

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <dlfcn.h>

static int (*orig_pthread_cond_broadcast)(pthread_cond_t *cond) = NULL;

__attribute__((constructor))
static void start() {
    orig_pthread_cond_broadcast =
        (int (*)()) dlsym(RTLD_NEXT, "pthread_cond_broadcast");
    if (orig_pthread_cond_broadcast == NULL) {
        printf("pthread_cond_broadcast not found!!!\n");
        exit(1);
    }
}

__attribute__((__visibility__("default")))
int pthread_cond_broadcast(pthread_cond_t *cond) {
    return orig_pthread_cond_broadcast(cond);
}

Simple pthread program:

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

pthread_mutex_t cond_mutex;
pthread_cond_t cond_var;
int condition;

void *thread0_work(void *arg) {
    pthread_mutex_lock(&cond_mutex);
    printf("Signal\n");
    condition = 1;
    pthread_cond_broadcast(&cond_var);
    pthread_mutex_unlock(&cond_mutex);
    return NULL;
}

void *thread1_work(void *arg) {
    pthread_mutex_lock(&cond_mutex);
    while (condition == 0) {
        printf("Wait\n");
        pthread_cond_wait(&cond_var, &cond_mutex);
        printf("Done waiting\n");
    }
    pthread_mutex_unlock(&cond_mutex);
    return NULL;
}

int main() {
    pthread_t thread1;

    pthread_mutex_init(&cond_mutex, NULL);
    pthread_cond_init(&cond_var, NULL);

    pthread_create(&thread1, NULL, thread1_work, NULL);

    // Slowdown this thread, so the thread 1 does pthread_cond_wait.
    usleep(1000);

    thread0_work(NULL);

    pthread_join(thread1, NULL);

    return 0;
}

EDIT:

For glibc 2.11.1 gdb bt gives:

(gdb) set environment LD_PRELOAD=./libintercept.so
(gdb) run
Starting program: /home/seguljac/intercept/main 
[Thread debugging using libthread_db enabled]
[New Thread 0x7ffff7436700 (LWP 19165)]
Wait
Signal
Before pthread_cond_broadcast

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff79ca0e7 in pthread_cond_broadcast@@GLIBC_2.3.2 () from /lib/libpthread.so.0
(gdb) bt
#0  0x00007ffff79ca0e7 in pthread_cond_broadcast@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007ffff7bdb769 in pthread_cond_broadcast () from ./libintercept.so
#2  0x00000000004008e8 in thread0_work ()
#3  0x00000000004009a4 in main ()

EDIT 2:

() R.. (!), , pthread_cond_broadcast , dlsym - . : http://blog.fesnel.com/blog/2009/08/25/preloading-with-multiple-symbol-versions/