netdev - Re: [Oops] fib_trie with ip route add throw since 2.6.25

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Date:	Mon, 7 Jul 2008 13:12:12 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	William Boughton <bill@...ghton.de>, netdev@...r.kernel.org,
	stephen.hemminger@...tta.com
Subject: Re: [Oops] fib_trie with ip route add throw since 2.6.25

On Mon, 7 Jul 2008 20:57:45 +0100
Ben Hutchings <bhutchings@...arflare.com> wrote:

> William Boughton wrote:
> > 
> > Hello,
> 
> Hello again!
> 
> > ip route add throw 192.168.0.1
> > 
> > ping 192.168.0.1
> > 
> > Oppses when CONFIG_IP_FIB_TRIE=y
> > 
> > Reproduced on both x86_64 and 32 on Xen and a normal
> > kernel running in qemu/kvm.
> > 
> > It seems this problem was introduced in 2.6.25
> > 
> > git bisect reports that it may have been caused by:
> > 
> > a07f5f508a4d9728c8e57d7f66294bf5b254ff7f is first bad commit                    
> > commit a07f5f508a4d9728c8e57d7f66294bf5b254ff7f                                 
> > Author: Stephen Hemminger <stephen.hemminger@...tta.com>                        
> > Date:   Tue Jan 22 21:53:36 2008 -0800                                          
> >                                                                                 
> >     [IPV4] fib_trie: style cleanup                                              
> >                                                                                 
> >     Style cleanups:                                                             
> >           * make check_leaf return -1 or plen, rather than by reference         
> [...]
> 
> The changes to check_leaf() and fn_trie_lookup() seem to be wrong - where
> fn_trie_lookup() would previously return a negative error value from
> check_leaf(), it now returns 0.
> 
> Now fn_trie_lookup() doesn't appear to care about plen, so we could revert
> check_leaf() to returning the error value.  How does this work?
> 
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 394db9c..43ed894 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -1357,17 +1357,17 @@ static int check_leaf(struct trie *t, struct leaf *l,
>  			t->stats.semantic_match_miss++;
>  #endif
>  		if (err <= 0)
> -			return plen;
> +			return err;
>  	}
>  
> -	return -1;
> +	return 1;
>  }
>  
>  static int fn_trie_lookup(struct fib_table *tb, const struct flowi *flp,
>  			  struct fib_result *res)
>  {
>  	struct trie *t = (struct trie *) tb->tb_data;
> -	int plen, ret = 0;
> +	int ret;
>  	struct node *n;
>  	struct tnode *pn;
>  	int pos, bits;
> @@ -1391,10 +1391,7 @@ static int fn_trie_lookup(struct fib_table *tb, const struct flowi *flp,
>  
>  	/* Just a leaf? */
>  	if (IS_LEAF(n)) {
> -		plen = check_leaf(t, (struct leaf *)n, key, flp, res);
> -		if (plen < 0)
> -			goto failed;
> -		ret = 0;
> +		ret = check_leaf(t, (struct leaf *)n, key, flp, res);
>  		goto found;
>  	}
>  
> @@ -1419,11 +1416,9 @@ static int fn_trie_lookup(struct fib_table *tb, const struct flowi *flp,
>  		}
>  
>  		if (IS_LEAF(n)) {
> -			plen = check_leaf(t, (struct leaf *)n, key, flp, res);
> -			if (plen < 0)
> +			ret = check_leaf(t, (struct leaf *)n, key, flp, res);
> +			if (ret > 0)
>  				goto backtrace;
> -
> -			ret = 0;
>  			goto found;
>  		}
> --- END ---
> 
> Ben.
> 

Agreed, a little more explanation would be good
   * return values?? fn_trie_lookup is same as fn_hash_lookup
   * check_leaf use return value of fn_trie_lookup so it can warpout without conditional
   * this needs some comments.

Note: in future since the route table is either hash or trie decided
at compile time, it would be worth getting rid of the indirection through
fib table functions. Looks like infrastructure was created but never used here.

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