Subject: Re: [Patch 3/3] net: reserve ports for applications using fixed port numbers

From: Cong Wang <[email-masked]>
Date: Tue, 13 Apr 2010 16:48:32 +0800

Cong Wang wrote:
> Tetsuo Handa wrote:
>> Hello.
>>
>>> --- linux-2.6.orig/drivers/infiniband/core/cma.c
>>> +++ linux-2.6/drivers/infiniband/core/cma.c
>>> @@ -1980,6 +1980,8 @@ retry:
>>>  	/* FIXME: add proper port randomization per like inet_csk_get_port */
>>>  	do {
>>>  		ret = idr_get_new_above(ps, bind_list, next_port, &port);
>>> +		if (!ret && inet_is_reserved_local_port(port))
>>> +			ret = -EAGAIN;
>>>  	} while ((ret == -EAGAIN) && idr_pre_get(ps, GFP_KERNEL));
>>>  
>>>  	if (ret)
>>>
>> I think above part is wrong. Below program
> ...
>> This result suggests that above loop will continue until idr_pre_get() fails
>> due to out of memory if all ports were reserved.
>>
>> Also, if idr_get_new_above() returned 0, bind_list (which is a kmalloc()ed
>> pointer) is already installed into a free slot (see comment on
>> idr_get_new_above_int()). Thus, simply calling idr_get_new_above() again will
>> install the same pointer into multiple slots. I guess it will malfunction later.
> 
> Thanks for testing!
> 
> How about:
> 
> +		if (!ret && inet_is_reserved_local_port(port))
> +			ret = -EBUSY;
> 
> ? So that it will break the loop and return error.
> 

Or use the similar trick:

 int tries = 10;
...

 if(!ret && inet_is_reserved_local_port(port)) {
   if (tries--)
     ret = -EAGAIN;
   else
     ret = -EBUSY;
 }

Any comments?