Date: Sun, 09 Dec 2012 00:50:05 +0100 From: Andre Oppermann <andre@freebsd.org> To: Richard Sharpe <rsharpe@richardsharpe.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Possible obscure socket leak when system under load and listener is slow to accept Message-ID: <50C3D22D.3060008@freebsd.org>
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> Hi folks,
>
> Our QA group (at xxx) using Samba and smbtorture has been seeing a
> lot of cases where accept returns ECONNABORTED because the system load
> is high and Samba has a large listen backlog.
>
> Every now and then we get a crash in smbd or in winbindd and winbindd
> complains of too many open files in the system.
>
> In looking at kern_accept, it seems to me that FreeBSD can leak a socket
> when kern_accept calls soaccept on it but gets ECONNABORTED. This error
> is the only error returned from tcp_usr_accept.
>
> It seems like the socket taken off so_comp is never freed in this case
> and that there has been a call on soref on it as well, so that something
> like the following is needed in the error path:
>
> ==== //some-path/freebsd/sys/kern/uipc_syscalls.c#1
> - /home/rsharpe/dev-src/packages/freebsd/sys/kern/uipc_syscalls.c ====
> @@ -433,6 +433,14 @@
> */
> if (name)
> *namelen = 0;
> + /*
> + * We need to close the socket we unlinked
> + * so we do not leak it.
> + */
> + ACCEPT_LOCK();
> + SOCK_LOCK(so);
> + soclose(so);
> goto noconnection;
> }
> if (sa == NULL) {
>
> I think an soclose is needed at this point because soisconnected has
> been called on the socket.
>
> Do you think this analysis is reasonable?
>
> We are using FreeBSD 8.0 but it seems the same is true for 9.0. However,
> maybe I am wrong since I am not sure if the fdclose call would free the
> socket, but a quick look suggested that it doesn't.
The fdclose should properly tear down the file descriptor. The call
graph is: fdclose() -> fdrop() -> _fdrop() -> fo_close()/soo_close() ->
soclose() -> sorele() -> sofree() -> sodealloc().
A socket leak would not count against "kern.maxfiles" unless the file
descriptor leaks as well. So it is unlikely that this is the problem.
Samba may open a large number of files (real files and sockets) and
you may run into the maxfiles limit. You can check the limit with
"sysctl kern.maxfiles" and increase it at boot time in boot/loader.conf
with "kern.maxfiles=100000" for example.
--
Andre
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