ipv6: frags: fix a lockdep false positive

lockdep does not know that the locks used by IPv4 defrag
and IPv6 reassembly units are of different classes.

It complains because of following chains :

1) sch_direct_xmit()        (lock txq->_xmit_lock)
    dev_hard_start_xmit()
     xmit_one()
      dev_queue_xmit_nit()
       packet_rcv_fanout()
        ip_check_defrag()
         ip_defrag()
          spin_lock()     (lock frag queue spinlock)

2) ip6_input_finish()
    ipv6_frag_rcv()       (lock frag queue spinlock)
     ip6_frag_queue()
      icmpv6_param_prob() (lock txq->_xmit_lock at some point)

We could add lockdep annotations, but we also can make sure IPv6
calls icmpv6_param_prob() only after the release of the frag queue spinlock,
since this naturally makes frag queue spinlock a leaf in lock hierarchy.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 2cdf3dc..b939b94 100644 (file)
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -163,7 +163,8 @@ fq_find(struct net *net, __be32 id, const struct ipv6hdr *hdr, int iif)
 }
 
 static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
-                          struct frag_hdr *fhdr, int nhoff)
+                         struct frag_hdr *fhdr, int nhoff,
+                         u32 *prob_offset)
 {
        struct sk_buff *prev, *next;
        struct net_device *dev;
@@ -179,11 +180,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
                        ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
 
        if ((unsigned int)end > IPV6_MAXPLEN) {
-               __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
-                               IPSTATS_MIB_INHDRERRORS);
-               icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
-                                 ((u8 *)&fhdr->frag_off -
-                                  skb_network_header(skb)));
+               *prob_offset = (u8 *)&fhdr->frag_off - skb_network_header(skb);
                return -1;
        }
 
@@ -214,10 +211,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
                        /* RFC2460 says always send parameter problem in
                         * this case. -DaveM
                         */
-                       __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
-                                       IPSTATS_MIB_INHDRERRORS);
-                       icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
-                                         offsetof(struct ipv6hdr, payload_len));
+                       *prob_offset = offsetof(struct ipv6hdr, payload_len);
                        return -1;
                }
                if (end > fq->q.len) {
@@ -519,15 +513,22 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
        iif = skb->dev ? skb->dev->ifindex : 0;
        fq = fq_find(net, fhdr->identification, hdr, iif);
        if (fq) {
+               u32 prob_offset = 0;
                int ret;
 
                spin_lock(&fq->q.lock);
 
                fq->iif = iif;
-               ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff);
+               ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff,
+                                    &prob_offset);
 
                spin_unlock(&fq->q.lock);
                inet_frag_put(&fq->q);
+               if (prob_offset) {
+                       __IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
+                                       IPSTATS_MIB_INHDRERRORS);
+                       icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, prob_offset);
+               }
                return ret;
        }