netdev - Re: ICMP packets - ll_temac with Microblaze

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Message-ID: <1324474811.2728.61.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Wed, 21 Dec 2011 14:40:11 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	monstr@...str.eu
Cc:	David Miller <davem@...emloft.net>,
	John Williams <john.williams@...alogix.com>,
	netdev@...r.kernel.org
Subject: Re: ICMP packets - ll_temac with Microblaze

Le mercredi 21 décembre 2011 à 14:28 +0100, Michal Simek a écrit :

> ok. Can you provide me any background why size should be setup by
> size = SKB_WITH_OVERHEAD(ksize(data));
> and not to use size which is passed to kmalloc in __alloc_skb.

Its all about memory accounting (based on skb->truesize)

Prior to the patch, we could fool memory accounting because skbs claimed
to use less memory than what they really used.

And crash machines eventually.

Now memory accouting is fixed, we probably need to change some points in
the kernel, where we previously accepted a small skb, but not a very
large one.

Since "ping" probably uses SOCK_RAW sockets, I'll try this one :

(We dont care of _this_ skb truesize, only on the count of previously
queued packets)


diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0da505c..a809a48 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1631,8 +1631,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (snaplen > res)
 		snaplen = res;
 
-	if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
-	    (unsigned)sk->sk_rcvbuf)
+	if (atomic_read(&sk->sk_rmem_alloc) >= (unsigned)sk->sk_rcvbuf)
 		goto drop_n_acct;
 
 	if (skb_shared(skb)) {
@@ -1763,7 +1762,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (po->tp_version <= TPACKET_V2) {
 		if (macoff + snaplen > po->rx_ring.frame_size) {
 			if (po->copy_thresh &&
-				atomic_read(&sk->sk_rmem_alloc) + skb->truesize
+				atomic_read(&sk->sk_rmem_alloc)
 				< (unsigned)sk->sk_rcvbuf) {
 				if (skb_shared(skb)) {
 					copy_skb = skb_clone(skb, GFP_ATOMIC);




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