[Libevent-users] Valgrind, evmap_io_add Invalid write of size 4

[Robin <imer@xxxxxxx>]

Hey,

I was just debugging some crashes and memory leaks with valgrind and 
this came up:
[warn] Epoll MOD(4) on fd 61 failed.  Old events were 6; read change was 
2 (del); write change was 0 (none): Bad file descriptor
> ==10706== Invalid write of size 4
> ==10706==    at 0x5348FE6: evmap_io_add (in 
> /usr/lib/i386-linux-gnu/libevent-2.0.so.5.1.7)
> ==10706==    by 0x5337BAA: event_add (in 
> /usr/lib/i386-linux-gnu/libevent-2.0.so.5.1.7)
> ==10706==    by 0x5343A57: _bufferevent_add_event (in 
> /usr/lib/i386-linux-gnu/libevent-2.0.so.5.1.7)
> ==10706==    by 0x53441DC: be_socket_enable (in 
> /usr/lib/i386-linux-gnu/libevent-2.0.so.5.1.7)
> ==10706==    by 0x5343475: bufferevent_enable (in 
> /usr/lib/i386-linux-gnu/libevent-2.0.so.5.1.7)
> ==10706==    by 0x806974F: net::Socket::Setup(int, sockaddr_in) 
> (Socket.cpp:77)
> ==10706==    by 0x8068A96: 
> net::Listener<net::socket::Client>::Accept(int, sockaddr_in*) 
> (Listener.hpp:85)
> ==10706==    by 0x806885A: 
> net::Listener<net::socket::Client>::SOnAccept(evconnlistener*, int, 
> sockaddr*, int, void*) (Listener.hpp:112)
> ==10706==    by 0x53462E1: listener_read_cb (in 
> /usr/lib/i386-linux-gnu/libevent-2.0.so.5.1.7)
> ==10706==    by 0x78BBD23D: ???
> ==10706==  Address 0x61d44e80 is 176 bytes inside a block of size 
> 4,056 free'd
> [...] Non libevent related stuff, some free'd memory which has nothing 
> to do with libevent

net::Listener:
>         void Accept(evutil_socket_t fd, sockaddr_in * addr) {
>             sys_log(0, "New connection on %s:%d from %s", 
> m_bind_ip.c_str(), m_bind_port, inet_ntoa(addr->sin_addr));
>             SocketType* s = new SocketType();
>             s->SetID(m_socket_id++);
>             if (!s->Setup(fd, *addr)) {
>                 sys_err("Failed to set up socket %d", m_socket_id);
>                 delete s;
>                 return;
>             }
>             if (!OnAccept(s)) {
>                 delete s;
>                 return;
>             }
>             m_sockets.insert(std::pair<unsigned int, 
> SocketType*>(s->GetID(), s));
>         }
>         static void SOnAccept(evconnlistener *, evutil_socket_t fd, 
> struct sockaddr * addr, int socklen, void * arg) {
>             if (!arg) {
>                 sys_err("Recieved nullpointer as arg");
>                 return;
>             }
>             Listener<SocketType>* l = (Listener<SocketType>*) arg;
>             l->Accept(fd, (sockaddr_in*) addr);
>         }
The callback is registered like this:
m_listener = 
evconnlistener_new_bind(NetworkManager::instance().GetEventBase(), 
Listener::SOnAccept, this, LEV_OPT_REUSEABLE | LEV_OPT_CLOSE_ON_FREE, 
1024, (sockaddr*) & sa, sizeof (sa));

 Socket::Setup:
>     bool Socket::Setup(evutil_socket_t fd, sockaddr_in addr) {
>         if (m_event) {
>             sys_err("Socket already set up");
>             return false;
>         }
>         m_addr = addr;
>         m_event = 
> bufferevent_socket_new(NetworkManager::instance().GetEventBase(), fd, 
> _SOCKET_DEFAULT_FLAGS);
>         bufferevent_setcb(m_event, Socket::SOnRead, Socket::SOnWrite, 
> Socket::SOnEvent, this);
>         bufferevent_enable(m_event, EV_READ | EV_WRITE);
>         OnConnect();
>         return true;
>     }
Is this just a false positive or am I doing something wrong?
This doesn't happen every time there's a new connection, in fact, it 
only seems to happen once

I am running on Debian Wheezy & libevent 2.0.19

I am also getting a bunch of these type errors:
> [warn] Epoll MOD(4) on fd 68 failed.  Old events were 6; read change 
> was 2 (del); write change was 0 (none): Bad file descriptor

Usually after it hit a breakpoint or it couldn't keep up (running this 
in a single thread+valgrind, stuff gets sloow)
Am I right to assume I can just ignore it as it only seems to happen 
when running valgrind?


- imer
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