Re: Reported regression against commit a05d2ad

Tim Gardner [off-list ref] writes:

On 06/21/2011 02:15 PM, Herton Ronaldo Krzesinski wrote:

quoted

Hi,

after update to one of the latest 2.6.32.x stable kernels for Ubuntu, we
got a regression report about timeout in tcp connections
(https://launchpad.net/bugs/791512).

We tried help reporter with a bisect process, but it was taking some
time, so we reverted some suspect commits, until we isolated it to
commit "af_unix: Only allow recv on connected seqpacket sockets."

With only commit a05d2ad reverted, testing results so far indicate the
issue doesn't happen.

I'm unfamiliar with unix sockets code, so can't see at first why this
commit in particular is causing problems, for now I can only say may be
something at application level using unix sockets regressed with it (?).
I'm just reporting it right now, and we plan to revert it for that kernel
until more info is found about it.

I'm adding reporter to CC (Lamont), in case more details are necessary
etc.

I believe we're also homing in on the same regression in 2.6.38.6 ('af_unix:
Only allow recv on connected seqpacket sockets.'). The functional part of the
patch is:

+
+       if (sk->sk_state != TCP_ESTABLISHED)
+               return -ENOTCONN;
+
+       return unix_dgram_recvmsg(iocb, sock, msg, size, flags);

What happens with out of order receives? Would fragmentation have an
impact?

That code path has absolutely nothing to do with packets that come in
over the wire.  Zilch, zero, nada.  Fragments don't matter because
fragments can not possibly hit that code path.  IP packets can not
possibly hit that code path.

Eric