Message-ID: <4BC42FE0.4040601@redhat.com>
Date: Tue, 13 Apr 2010 16:48:32 +0800
From: Cong Wang <amwang@redhat.com>
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To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
CC: opurdila@ixiacom.com, eric.dumazet@gmail.com, netdev@vger.kernel.org,
       nhorman@tuxdriver.com, davem@davemloft.net, ebiederm@xmission.com,
       linux-kernel@vger.kernel.org
Subject: Re: [Patch 3/3] net: reserve ports for applications using fixed port
 numbers
References: <20100412100744.5302.92442.sendpatchset@localhost.localdomain> <20100412100816.5302.74919.sendpatchset@localhost.localdomain> <201004130121.o3D1Lhh7099571@www262.sakura.ne.jp> <4BC41994.7030707@redhat.com>
In-Reply-To: <4BC41994.7030707@redhat.com>
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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?
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