Re: [NFS] [PATCH 2/7] SUNRPC: Fix TCP rebinding logic

[Chuck Lever <chuck.lever@oracle.com>]

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Trond Myklebust wrote:
> On Wed, 2007-11-07 at 17:48 -0500, Chuck Lever wrote:
>> Trond Myklebust wrote:
>>>  static int xs_bind4(struct sock_xprt *transport, struct socket *sock)
>>>  {
>>>  	struct sockaddr_in myaddr = {
>>>  		.sin_family = AF_INET,
>>>  	};
>>>  	struct sockaddr_in *sa;
>>> -	int err;
>>> -	unsigned short port = transport->port;
>>> +	int err, nloop = 0;
>>> +	unsigned short port = xs_get_srcport(transport, sock);
>>> +	unsigned short last;
>>>  
>>> -	if (!transport->xprt.resvport)
>>> -		port = 0;
>>>  	sa = (struct sockaddr_in *)&transport->addr;
>>>  	myaddr.sin_addr = sa->sin_addr;
>>>  	do {
>>>  		myaddr.sin_port = htons(port);
>>>  		err = kernel_bind(sock, (struct sockaddr *) &myaddr,
>>>  						sizeof(myaddr));
>>> -		if (!transport->xprt.resvport)
>>> +		if (port == 0)
>>>  			break;
>>>  		if (err == 0) {
>>>  			transport->port = port;
>>>  			break;
>>>  		}
>>> -		if (port <= xprt_min_resvport)
>>> -			port = xprt_max_resvport;
>>> -		else
>>> -			port--;
>>> -	} while (err == -EADDRINUSE && port != transport->port);
>>> +		last = port;
>>> +		port = xs_next_srcport(transport, sock, port);
>>> +		if (port > last)
>>> +			nloop++;
>> It seems like there are cases where a user can adjust the port range and 
>> it would defeat this check.  For example, if the port range is 30 to 40, 
>> and the user changes it to 10 to 20, we keep looping.
> 
> Yes, but once we hit 10, then the nloop gets bumped. It is guaranteed to
> get bumped if we hit 0, or if the administrator increases the minimum
> port number past the current one.
> 
>> Doesn't breaking out of the loop break "Hard" NFS requests?
> 
> We've always had to deal with breaking out of the loops. If we don't, we
> will deadlock the computer.

In that case it might make sense to allow some scheduling between each 
socket bind attempt, and do only a single pass over the port range 
before breaking out.  Then you could forget about whether the range 
changes -- you will use the new range the next time a connection is 
attempted.

> If this is a hard mount, then the only result should normally be that we
> abort the connection,  time out, and then try again. This has been the
> behaviour for quite some while.

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