freebsd stable - May 2007 - UNIX domain sockets MFC's

Dear all,

I have just completed the merge of a significant number of UNIX domain socket 
bug fixes and cleanups from HEAD to RELENG_6.  While my hope is that these are 
generally low-risk, and should improve UNIX domain socket stability and 
performance under load, there were quite a few changes involved.  As such, 
please keep an eye out for any new problems with UNIX domain sockets, and drop 
me an e-mail if you run into any.  The changes in the recent MFC spree 
include:

- Additional MAC check for UNIX domain socket connect().

- Cleanup of structure, comments, white space, and consolidation of
   uipc_proto.c into uipc_usrreq.c.  Removal of redundant code.

- Fixed races involving simultaneous bind() and connect() between two threads
   or processes on the same UNIX domain socket.

- Reduced period of overlapped acquisition of socket buffer mutexes during
   send/receive, which should lower lock contention under load.

Right now I am tracking two known issues with UNIX domain sockets in RELENG_6:

- Reported NULL point derference in unp_connect(), which occurs due to the
   dropping of locks around sonewconn().  This is fixed in HEAD, and I am
   preparing an MFC of this patch.

- Reported UNIX domain socket connection leak.  This is not yet fully
   diagnosed.

Robert N M Watson
Computer Laboratory
University of Cambridge

On Tue, 8 May 2007, Robert Watson wrote:
> Right now I am tracking two known issues with UNIX domain sockets in 
> RELENG_6:
>
> - Reported NULL point derference in unp_connect(), which occurs due to the
>  dropping of locks around sonewconn().  This is fixed in HEAD, and I am
>  preparing an MFC of this patch.
The fix for this has now been merged as 1.155.2.22.  As there have been no new 
reports of UNIX domain socket problems in the last couple of days, it sounds 
like the MFC of the last batch of fixes and cleanups has not lead to problems.

Robert N M Watson
Computer Laboratory
University of Cambridge

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- --On Monday, May 14, 2007 11:29:12 +0100 Robert Watson
<rwatson@FreeBSD.org>
wrote:
>
> On Sat, 12 May 2007, Marc G. Fournier wrote:
>
>>> The fix for this has now been merged as 1.155.2.22.  As there have
been no
>>> new reports of UNIX domain socket problems in the last couple of
days, it
>>> sounds like the MFC of the last batch of fixes and cleanups has not
lead to
>>> problems.
>>
>> I've just upgraded my kernel to the latest, to include the
MFC'd code above
>> ...
>
> Yes -- I was very specific in my e-mail regarding the MFC's that they
were
> not believed to address the problem you are reporting.  I think we have a
> leak in the way some edge case is handled with regard to UNIX domain socket
> shutdown. What would be really nice to know is if that persists in
7-CURRENT,
> in which we've redone the way the socket life cycle works.  However, I
don't
> know if you are able to tolerate booting a 7-CURRENT kernel in your
> environment...?
On that server, that could be very difficult ... if this was happening on any 
of my HP servers, I would in a minute ...
> Did we determine whether backing out to before the unpcb socket reference
> count change made any difference for you?
The problem appeared to persist after backing it out ...

I'm curious about something ... way back, when I was using unionfs, I had a 
major problem with vnode leakage ... as I mentioned before, this server is the 
only one I have that uses geom/gmirror on its drives, the rest all use hardware 
RAID ... is there *any* possibility that I'm seeing some sort of interaction
issue?  It really bothers me that the only server that I'm seeing this one
is
the one that I'm using software RAID on ...

Would it be useful to add some DEBUG statements to the socket code, to trace 
open/close/flush/etc?  Maybe to see where flush's are being started, but
never
completed?  That sort of thing?


- ----
Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email . scrappy@hub.org                              MSN . scrappy@hub.org
Yahoo . yscrappy               Skype: hub.org        ICQ . 7615664
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