netdev - Re: [PATCH] fix NULL pointer + success return in route lookup path

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Date:	Sat, 20 Jun 2009 18:39:25 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	netdev@...r.kernel.org, mbizon@...ebox.fr, dada1@...mosbay.com,
	kuznet@....inr.ac.ru, davem@...emloft.net, pekkas@...core.fi,
	jmorris@...ei.org, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH] fix NULL pointer + success return in route lookup path

Jarek Poplawski wrote, On 06/20/2009 02:37 PM:

> Neil Horman wrote, On 06/19/2009 07:18 PM:
> 
>> Don't drop route if we're not caching	

...

>>  route.c |   14 ++++++++++++--
>>  1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
>> index cd76b3c..65b3a8b 100644
>> --- a/net/ipv4/route.c
>> +++ b/net/ipv4/route.c
>> @@ -1085,8 +1085,16 @@ restart:
>>  	now = jiffies;
>>  
>>  	if (!rt_caching(dev_net(rt->u.dst.dev))) {
>> -		rt_drop(rt);


One more question: if this rt is assigned to an skb, there is only
skb_dst_drop() in kfree_skb(), but it seems we skip rt_free() part,
or I miss something?

Jarek P.

>> -		return 0;
>> +		/*
>> +		 * If we're not caching, just tell the caller we
>> +		 * were successful and don't touch the route.  The
>> +		 * caller hold the sole reference to the cache entry, and
>> +		 * it will be released when the caller is done with it.
>> +		 * If we drop it here, the callers have no way to resolve routes
>> +		 * when we're not caching.  Instead, just point *rp at rt, so
>> +		 * the caller gets a single use out of the route
>> +		 */
>> +		goto report_and_exit;
>>  	}
>>  
>>  	rthp = &rt_hash_table[hash].chain;
>> @@ -1217,6 +1225,8 @@ restart:
>>  	rcu_assign_pointer(rt_hash_table[hash].chain, rt);
>>  
>>  	spin_unlock_bh(rt_hash_lock_addr(hash));
>> +
>> +report_and_exit:
>>  	if (rp)
>>  		*rp = rt;
>>  	else


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