netdev - Re: nfs broken in net-next? -- now in mainline -- bisected: d9f5950f90292f7cc42834338dfd5f44dc4cc4ca

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Date:	Sun, 13 Dec 2009 14:28:14 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, mingo@...e.hu, sri@...ibm.com,
	herbert@...dor.apana.org.au, torvalds@...ux-foundation.org,
	sjayaraman@...e.de, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: nfs broken in net-next? -- now in mainline -- bisected: d9f5950f90292f7cc42834338dfd5f44dc4cc4ca

Eric Dumazet wrote:
> Le 13/12/2009 03:41, Yinghai Lu a écrit :
>>>> cause the problem: nfs mount fail.
>>>>
>>>> the setup is:
>>>> 64bit kernel, have all needed drivers in kernel, and boot with
>>>> ip=dhcp, root disk is 256M ramdisk.
>>>> then try to mount nfs....
>>>>
>>> change entries default value from 65536 to 256,
>>> nfs mount will work.
>>>
>> interesting:
>>
>> m:~/dump # grep UDP dmesg.txt
>> [   28.996034] UDP hash table entries: 65536 (order: 11, 10485760 bytes)
>> [   29.032364] UDP-Lite hash table entries: 65536 (order: 11, 10485760 bytes)
>>
>> will not work
>>
>> but 32768 will work.
> 
> Thanks a lot for this work Yinghai !
> This last bit helped me a lot ...
> 
> Hmm, udp_lib_get_port() assumes it can loop at least one time in :
> 
> for (last = first + udptable->mask + 1;
> 	first != last;
> 	first++) {
> // unit_work
> }
> 
> but if udptable->mask == 65535, loop is not entered at all (since last == first)
> 
> We should convert it to a do { } while(...); construct, or use 32bit variables
> and (u16) casts.
> 
> Thanks
> 
> [PATCH] udp: udp_lib_get_port() fix
> 
> Now we can have a large udp hash table, udp_lib_get_port() loop
> should be converted to a do {} while (cond) form,
> or we dont enter it at all if hash table size is exactly 65536.
> 
> Reported-by: Yinghai Lu <yinghai@...nel.org>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 1f95348..f0126fd 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -216,9 +216,8 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
>  		 * force rand to be an odd multiple of UDP_HTABLE_SIZE
>  		 */
>  		rand = (rand | 1) * (udptable->mask + 1);
> -		for (last = first + udptable->mask + 1;
> -		     first != last;
> -		     first++) {
> +		last = first + udptable->mask + 1;
> +		do {
>  			hslot = udp_hashslot(udptable, net, first);
>  			bitmap_zero(bitmap, PORTS_PER_CHAIN);
>  			spin_lock_bh(&hslot->lock);
> @@ -238,7 +237,7 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
>  				snum += rand;
>  			} while (snum != first);
>  			spin_unlock_bh(&hslot->lock);
> -		}
> +		} while (++first != last);
>  		goto fail;
>  	} else {
>  		hslot = udp_hashslot(udptable, net, snum);

thanks. that fix the problem.

YH
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