Date: Thu, 14 Dec 2000 06:17:40 -0800 From: Julian Elischer <julian@elischer.org> To: Alfred Perlstein <bright@wintelcom.net> Cc: Matt Dillon <dillon@earth.backplane.com>, Kirk McKusick <mckusick@mckusick.com>, arch@FreeBSD.ORG, net@FreeBSD.ORG Subject: Re: patch to cleanup inflight desciptor handling. Message-ID: <3A38D684.F241D6B9@elischer.org> References: <200012131852.KAA17423@beastie.mckusick.com> <200012132106.eBDL6Sg86570@earth.backplane.com> <20001213141917.Q16205@fw.wintelcom.net> <20001213145341.S16205@fw.wintelcom.net>
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Alfred Perlstein wrote:
>
> * Alfred Perlstein <bright@wintelcom.net> [001213 14:20] wrote:
> > * Matt Dillon <dillon@earth.backplane.com> [001213 13:07] wrote:
> > > :I believe that your changes have been sorely needed for many
> > > :years. While I would like to see regular mbufs given a callback
> > > :mechanism, your present approach of using an mbuf cluster
> > > :solves 90% of the problem.
> > > :
> > > : Kirk McKusick
> > >
> > > ... Aflred, be careful that you don't break things we only just fixed
> > > last year. The descriptor passing code has been broken for many years.
> > >
> > > I think the reason we have to scan the descriptor list is related to
> > > locating isolated self-referential 'loops' with descriptor passing and
> > > unix domain sockets and closing them. e.g. when you pass a descriptor
> > > for a unix-domain socket through a unix-domain socket, it is possible
> > > for the socket descriptors to reference each other and thus never have
> > > their ref count drop to 0 even when all associated processes have
> > > close()'d. This happens all the time. Be sure you don't break the
> > > fix that solves that particular problem.
> >
> > Ok, I'll see if that can happen. Basically since the reference
> > never goes to zero on the socket, the buffers are never forced to
> > be flushed/cleared and the mbuf will then never be free'd resulting
> > it it leaking itself. Basically a socket hanging there with an
> > mbuf referencing itself.
> >
> > I wonder if Linux fixed/has this problem.
>
> Ok, my patch has this problem:
>
> void
> parent(int con)
> {
> int fd;
>
> fd = open("/tmp/wank", O_RDONLY);
> send_fd_withdata(con, con, "wank", 4);
> sleep (5);
> exit(1);
>
> }
>
> void
> child(int con)
> {
> int fd, error;
> char buf[100];
>
> sleep(5);
> get_fd_withdata(con, &fd, buf, sizeof(buf));
> send_fd_withdata(con, fd, "foo", 3);
> exit(1);
> buf[4] = '\0';
> printf("%s\n", buf);
> if ((error = read(fd, buf, sizeof(buf))) < 0)
> perror("read");
> buf[sizeof(buf)-1] = '\0';
> printf("%s\n", buf);
>
>
> }
>
> This causes a leak, I think the trick is to just always call sorflush()
> when the pcb is free'd.
that's what I was trying to point out to you....
It get's more complicate when you have 2 pipes, and each has the
filedescriptors for the other one in it.
>
> Looking at linux they still are using gc. I'll give this a lot
> more thought before resubmitting this idea.
>
> sorry,
> --
> -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
> "I have the heart of a child; I keep it in a jar on my desk."
>
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--
__--_|\ Julian Elischer
/ \ julian@elischer.org
( OZ ) World tour 2000
---> X_.---._/ presently in: Budapest
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