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Subject[PATCH 4.9 37/41] ipv6: frags: fix a lockdep false positive
Date
From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 415787d7799f4fccbe8d49cb0b8e5811be6b0389 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/reassembly.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)

--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -169,7 +169,8 @@ fq_find(struct net *net, __be32 id, cons
}

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;
@@ -185,11 +186,7 @@ static int ip6_frag_queue(struct frag_qu
((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));

if ((unsigned int)end > IPV6_MAXPLEN) {
- __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
- 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;
}

@@ -220,10 +217,7 @@ static int ip6_frag_queue(struct frag_qu
/* RFC2460 says always send parameter problem in
* this case. -DaveM
*/
- __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
- 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) {
@@ -524,15 +518,22 @@ static int ipv6_frag_rcv(struct sk_buff
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, ip6_dst_idev(skb_dst(skb)),
+ IPSTATS_MIB_INHDRERRORS);
+ icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, prob_offset);
+ }
return ret;
}


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