On Wed, 2012-06-27 at 15:28 -0400, Jeff Layton wrote:
> On Wed, 27 Jun 2012 18:43:56 +0000
> "Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> wrote:
> > The reason why we close these sockets is that if the attempt at aborting
> > the connection fails, then they typically end up in a TIME_WAIT state.
> >
>
> I'm still trying to wade through the xprtsock.c socket handling code,
> but it looks like we currently tear down the connection in 3 different
> ways:
>
> xs_close: which basically calls sock_release and gets rid of our
> reference to an existing socket. Most of the places where we disconnect
> the socket use this. After this, we end up with srcport == 0 which
> makes it pick a new port.
>
> xs_tcp_shutdown: which calls ->shutdown on it, but doesn't free
> anything. This also preserves the existing srcport.
>
> xs_abort_connection: calls kernel_connect to reconnect the socket to
> AF_UNSPEC address (effectively disconnecting it?). This also preserves
> the srcport. I guess we use this just before reconnecting when the
> remote end drops the connection, since we don't need to be graceful
> about tearing anything down at that point.
>
> The last one actually does reuse the same socket, so my thinking was
> that we could extend that scheme to the other cases. If we called
> ->shutdown on it and then reconnected it to AF_UNSPEC, would that
> "reset" it back to a usable state?
Not that I'm aware of. The problem is that most of this stuff is
undocumented. For instance, the AF_UNSPEC reconnect is documented only
for UDP connections. While Linux implements it for TCP too, there is no
spec (that I'm aware of) that explains how that should work.
> If there really is no alternative to freeing the socket, then the only
> real fix I can see is to set PF_MEMALLOC when we go to create it and
> then reset it afterward. That's a pretty ugly fix though...
Agreed...
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
��.n��������+%������w��{.n�����{��w��� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
