[Bug libc/16524] New: eventfd_write() doesn't work when 2nd argument is zero

["structurechart at yahoo dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16524

            Bug ID: 16524
           Summary: eventfd_write() doesn't work when 2nd argument is zero
           Product: glibc
           Version: 2.12
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: structurechart at yahoo dot com
                CC: drepper.fsp at gmail dot com

Hi,

I searched for eventfd_write in bugzilla here but I don't see any bug.

Hope that I don't file a bug that has been fixed.

The problem is that when eventfd() is called with 2nd argument=0, epoll_wait()
never returns, but when the argument is set to 1.  epoll_wait() returns.

Here is how I reproduce:
./bug 0

It never returns.

./bug 1

It returns.

Here is the code:
#include <sys/epoll.h>
#include <sys/eventfd.h>
#include <assert.h>
#include <cstdlib>
#include <iostream>

int value = 0;
int efd = 0;

void* start(void* p) {
    std::cout << __PRETTY_FUNCTION__ << ": going to sleep for 5 sec" <<
std::endl;
    sleep(5);
    std::cout << __PRETTY_FUNCTION__ << ": going to call eventfd_write() with
value=" << value << std::endl;
    const int rc = eventfd_write(efd, value);
    assert(0 == rc);
    return NULL;
}

int main(int argc, char** argv) {
    const int epFD = epoll_create1(0);
    assert(-1 != epFD);

    efd = eventfd(0, 0);
    assert(-1 != efd);

    struct epoll_event event;
    event.data.fd = efd;
    event.events = EPOLLIN;
    epoll_ctl(epFD, EPOLL_CTL_ADD, efd, &event);

    value = strtoul(argv[1], NULL, 10);

    const uint32_t nEvents = 2;
    struct epoll_event events[nEvents];

    pthread_t threadID;
    const int rc = pthread_create(&threadID, NULL, &start, NULL);
    assert(0 == rc);

    sleep(1);

    std::cout << __PRETTY_FUNCTION__ << ": going to wait for event" <<
std::endl;

    int n = epoll_wait(epFD, events, nEvents, -1);
    assert(n > 0);

    std::cout << "okay" << std::endl;

    return 0;
}

Here is how I compiled:
g++ -Wall bug.cpp -o bug -O3 -lpthread

Here is my glibc version:
$ rpm -qa | grep glibc
glibc-devel-2.12-1.132.el6.x86_64
glibc-common-2.12-1.132.el6.x86_64
glibc-2.12-1.132.el6.x86_64
glibc-2.12-1.132.el6.i686
glibc-headers-2.12-1.132.el6.x86_64

Here is my g++ version:
$ g++ --version
g++ (GCC) 4.4.7 20120313 (Red Hat 4.4.7-3)
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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