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From: Eric Dumazet <eric.dumazet@gmail•com>
To: Yinghai Lu <yinghai@kernel•org>
Cc: David Miller <davem@davemloft•net>,
	mingo@elte•hu, sri@us•ibm.com, herbert@gondor•apana.org.au,
	torvalds@linux-foundation•org, sjayaraman@suse•de,
	linux-kernel@vger•kernel.org, netdev@vger•kernel.org
Subject: Re: nfs broken in net-next? -- now in mainline -- bisected: d9f5950f90292f7cc42834338dfd5f44dc4cc4ca
Date: Sun, 13 Dec 2009 17:57:08 +0100	[thread overview]
Message-ID: <4B251CE4.9080401@gmail.com> (raw)
In-Reply-To: <86802c440912121841j34cde8ecv892d7d74a32313ac@mail.gmail.com>

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@kernel•org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail•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);

  reply	other threads:[~2009-12-13 16:58 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-12-12  5:25 nfs broken in net-next? -- now in mainline -- bisected: d9f5950f90292f7cc42834338dfd5f44dc4cc4ca Yinghai Lu
2009-12-12  5:41 ` David Miller
2009-12-13  1:05   ` Yinghai Lu
2009-12-13  1:57     ` Yinghai Lu
2009-12-13  2:25       ` Yinghai Lu
2009-12-13  2:41         ` Yinghai Lu
2009-12-13 16:57           ` Eric Dumazet [this message]
2009-12-13 22:28             ` Yinghai Lu
2009-12-14  3:33               ` David Miller

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