netdev - Re: virt-manager broken by bind(0) in net-next.

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Message-ID: <20090130215008.GB12210@ioremap.net>
Date:	Sat, 31 Jan 2009 00:50:08 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, berrange@...hat.com,
	et-mgmt-tools@...hat.com, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: virt-manager broken by bind(0) in net-next.

On Fri, Jan 30, 2009 at 07:41:59PM +0100, Eric Dumazet (dada1@...mosbay.com) wrote:
> Reviewing commit a9d8f9110d7e953c2f2b521087a4179677843c2a
> 
> I see use of a hashinfo->bsockets field that :
> 
> - lacks proper lock/synchronization

It should contain rough number of sockets, there is no need to be very
precise because of this hueristic.

> - suffers from cache line ping pongs on SMP

I used free alignment slot so that socket structure would not be
icreased.

> Also there might be a problem at line 175
> 
> if (sk->sk_reuse && sk->sk_state != TCP_LISTEN && --attempts >= 0) { 
> 	spin_unlock(&head->lock);
> 	goto again;
> 
> If we entered inet_csk_get_port() with a non null snum, we can "goto again"
> while it was not expected.
> 
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index df8e72f..752c6b2 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -172,7 +172,8 @@ tb_found:
>  		} else {
>  			ret = 1;
>  			if (inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb)) {
> -				if (sk->sk_reuse && sk->sk_state != TCP_LISTEN && --attempts >= 0) {
> +				if (sk->sk_reuse && sk->sk_state != TCP_LISTEN &&
> +					smallest_size == -1 &&  --attempts >= 0) {

I think it should be smallest_size != -1, since we really want to goto
to the again label when hueristic is used, which in turn changes
smallest_size.

-- 
	Evgeniy Polyakov
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