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[SCTP][patch] socket does not wake up

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Next thread: kill hangs with csh by Nathan Lay on Wednesday, October 3, 2007 - 10:50 am. (1 message)
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From: Martin Kulas
Subject: [SCTP][patch] socket does not wake up
Date: Wednesday, October 3, 2007 - 7:14 am

Hello!

I patched netcat to support 1to1-SCTP sockets.
Netcat uses the poll() system call to wait for new data
in the socket buffer.  The problem is that poll() does not
return when the kernel has closed the SCTP association.
Select() has the same problem.

I digged around in the SCTP sources and created a patched to remove=20
that bug.   The patch is a one-liner:

<patch>
--- sctp_pcb.c.orig	2007-10-03 13:27:12.000000000 +0200
+++ sctp_pcb.c	2007-10-03 15:51:55.286987000 +0200
@@ -4234,6 +4234,7 @@
 					    SS_ISCONFIRMING |
 					    SS_ISCONNECTED);
 				}
+				socantrcvmore(so);
 				SOCK_UNLOCK(so);
 				sctp_sowwakeup(inp, so);
 				sctp_sorwakeup(inp, so);
</patch>

Now I have no problems with the system calls select()/poll() anymore.
Is this patch OK or have I missed anything?


Regards,
Martin

--=20
PGP Key: http://www.stud.uni-hamburg.de/~kulas/mkulas_pubkey.asc

[ message continues ]
[view original message]
From: Randall Stewart
Subject: Re: [SCTP][patch] socket does not wake up
Date: Wednesday, October 3, 2007 - 3:51 pm

Martin:

Thanks for the patch.. note that I will submit it to
re for approval after a minor fix.

socantrcvmore(so);

assumes you do NOT hold a lock.  This code holds
the socket lock.. which is the recv sockbuf lock..

So if you turn witness on your kernel and run with this
you will have a double lock.. panic.

Note to fix this right you should have it be:
  				SOCK_UNLOCK(so);
+				socantrcvmore(so);

Which is what I will submit to release ops.. you may want
to change this in what you are working with so you don;t
have some other side-effect issue from the double lock.. like
leaking sockets.

R



-- 
Randall Stewart
NSSTG - Cisco Systems Inc.
803-345-0369 <or> 803-317-4952 (cell)
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From: Aryeh Friedman
Subject: Re: [SCTP][patch] socket does not wake up
Date: Wednesday, October 3, 2007 - 4:33 pm

Does this solve the many issues with warning messages and syn/ack
being received after close and such?  Also I think this might also be
related to the re(3) patch I mentioned in an other thread
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From: Randall Stewart
Subject: Re: [SCTP][patch] socket does not wake up
Date: Wednesday, October 3, 2007 - 4:41 pm

This is SCTP not TCP... so no I don't think it will help any
syn-ack problems.

R

-- 
Randall Stewart
NSSTG - Cisco Systems Inc.
803-345-0369 <or> 803-317-4952 (cell)
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[view original message]
From: Martin Kulas
Subject: Re: [SCTP][patch] socket does not wake up
Date: Thursday, October 4, 2007 - 1:51 pm

Oops, of course, that is the right fix.

Regards,
Martin

--=20
PGP Key: http://sosend.de/mk/coolaz_web_de.pub.asc

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