linux-kernel - Re: [NFS] [patch] sunrpc: make closing of old temporary sockets work (was: problems with lockd in 2.6.22.6)

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Message-ID: <20070912133729.GA24998@fieldses.org>
Date:	Wed, 12 Sep 2007 09:37:29 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Wolfgang Walter <wolfgang.walter@...dentenwerk.mhn.de>
Cc:	trond.myklebust@....uio.no, netdev@...r.kernel.org,
	nfs@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [NFS] [patch] sunrpc: make closing of old temporary sockets
	work (was: problems with lockd in 2.6.22.6)

On Wed, Sep 12, 2007 at 02:07:10PM +0200, Wolfgang Walter wrote:
> as already described old temporary sockets (client is gone) of lockd aren't
> closed after some time. So, with enough clients and some time gone, there
> are 80 open dangling sockets and you start getting messages of the form:
> 
> lockd: too many open TCP sockets, consider increasing the number of nfsd threads.

Thanks for working on this problem!

> If I understand the code then the intention was that the server closes
> temporary sockets after about 6 to 12 minutes:
> 
> 	a timer is started which calls svc_age_temp_sockets every 6 minutes.
> 
> 	svc_age_temp_sockets:
> 		if a socket is marked OLD it gets closed.
> 		sockets which are not marked as OLD are marked OLD
> 
> 	every time the sockets receives something OLD is cleared.
> 
> But svc_age_temp_sockets never closes any socket though because it only
> closes sockets with svsk->sk_inuse == 0. This seems to be a bug.
> 
> Here is a patch against 2.6.22.6 which changes the test to
> svsk->sk_inuse <= 0 which was probably meant. The patched kernel runs fine
> here. Unused sockets get closed (after 6 to 12 minutes)

So the fact that this changes the behavior means that sk_inuse is taking
on negative values.  This can't be right--how can something like
svc_sock_put() (which does an atomic_dec_and_test) work in that case?

I wish I had time today to figure out what's going on in this case.  But
from a quick through svsock.c for sk_inuse, it looks odd; I'm suspicious
of anything without the stereotyped behavior--initializing to one,
atomic_inc()ing whenever someone takes a reference, and
atomic_dec_and_test()ing whenever someone drops it....

--b.
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