netdev - [RFC PATCH 01/11] net: add support for noref skb->sk

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Date:   Fri, 22 Sep 2017 23:06:25 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: [RFC PATCH 01/11] net: add support for noref skb->sk

Noref sk do not carry a socket refcount, are valid
only inside the current RCU section and must be
explicitly cleared before exiting such section.

They will be used in a later patch to allow early demux
without sock refcounting.

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 include/linux/skbuff.h | 31 +++++++++++++++++++++++++++++++
 net/core/sock.c        |  7 +++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 492828801acb..c3fc32636690 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -922,6 +922,37 @@ static inline struct rtable *skb_rtable(const struct sk_buff *skb)
 	return (struct rtable *)skb_dst(skb);
 }
 
+void sock_dummyfree(struct sk_buff *skb);
+
+/* only early demux can set noref socks
+ * noref socks do not carry any refcount and must be
+ * cleared before exiting the current RCU section
+ */
+static inline void skb_set_noref_sk(struct sk_buff *skb, struct sock *sk)
+{
+	skb->sk = sk;
+	skb->destructor = sock_dummyfree;
+}
+
+static inline bool skb_has_noref_sk(struct sk_buff *skb)
+{
+	return skb->destructor == sock_dummyfree;
+}
+
+static inline struct sock *skb_clear_noref_sk(struct sk_buff *skb)
+{
+	struct sock *ret;
+
+	if (!skb_has_noref_sk(skb))
+		return NULL;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+	ret = skb->sk;
+	skb->sk = NULL;
+	skb->destructor = NULL;
+	return ret;
+}
+
 /* For mangling skb->pkt_type from user space side from applications
  * such as nft, tc, etc, we only allow a conservative subset of
  * possible pkt_types to be set.
diff --git a/net/core/sock.c b/net/core/sock.c
index 9b7b6bbb2a23..33da8e7e58a0 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1893,6 +1893,13 @@ void sock_efree(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(sock_efree);
 
+/* dummy destructor used by noref sockets */
+void sock_dummyfree(struct sk_buff *skb)
+{
+	WARN_ON_ONCE(!rcu_read_lock_held());
+}
+EXPORT_SYMBOL(sock_dummyfree);
+
 kuid_t sock_i_uid(struct sock *sk)
 {
 	kuid_t uid;
-- 
2.13.5