netfilter: conntrack: avoid useless indirection during conntrack destruction

nf_ct_put() results in a usesless indirection:

nf_ct_put -> nf_conntrack_put -> nf_conntrack_destroy -> rcu readlock +
indirect call of ct_hooks->destroy().

There are two _put helpers:
nf_ct_put and nf_conntrack_put.  The latter is what should be used in
code that MUST NOT cause a linker dependency on the conntrack module
(e.g. calls from core network stack).

Everyone else should call nf_ct_put() instead.

A followup patch will convert a few nf_conntrack_put() calls to
nf_ct_put(), in particular from modules that already have a conntrack
dependency such as act_ct or even nf_conntrack itself.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/linux/netfilter/nf_conntrack_common.h b/include/linux/netfilter/nf_conntrack_common.h
index a03f7a8..2770db2 100644 (file)
--- a/include/linux/netfilter/nf_conntrack_common.h
+++ b/include/linux/netfilter/nf_conntrack_common.h
@@ -29,6 +29,8 @@ struct nf_conntrack {
 };
 
 void nf_conntrack_destroy(struct nf_conntrack *nfct);
+
+/* like nf_ct_put, but without module dependency on nf_conntrack */
 static inline void nf_conntrack_put(struct nf_conntrack *nfct)
 {
        if (nfct && refcount_dec_and_test(&nfct->use))

diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index a4a14f3..8731d5b 100644 (file)
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -76,6 +76,8 @@ struct nf_conn {
         * Hint, SKB address this struct and refcnt via skb->_nfct and
         * helpers nf_conntrack_get() and nf_conntrack_put().
         * Helper nf_ct_put() equals nf_conntrack_put() by dec refcnt,
+        * except that the latter uses internal indirection and does not
+        * result in a conntrack module dependency.
         * beware nf_ct_get() is different and don't inc refcnt.
         */
        struct nf_conntrack ct_general;
@@ -170,11 +172,13 @@ nf_ct_get(const struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
        return (struct nf_conn *)(nfct & NFCT_PTRMASK);
 }
 
+void nf_ct_destroy(struct nf_conntrack *nfct);
+
 /* decrement reference count on a conntrack */
 static inline void nf_ct_put(struct nf_conn *ct)
 {
-       WARN_ON(!ct);
-       nf_conntrack_put(&ct->ct_general);
+       if (ct && refcount_dec_and_test(&ct->ct_general.use))
+               nf_ct_destroy(&ct->ct_general);
 }
 
 /* Protocol module loading */

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index cd3d07e..7a2063a 100644 (file)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -558,7 +558,7 @@ static void nf_ct_del_from_dying_or_unconfirmed_list(struct nf_conn *ct)
 
 #define NFCT_ALIGN(len)        (((len) + NFCT_INFOMASK) & ~NFCT_INFOMASK)
 
-/* Released via destroy_conntrack() */
+/* Released via nf_ct_destroy() */
 struct nf_conn *nf_ct_tmpl_alloc(struct net *net,
                                 const struct nf_conntrack_zone *zone,
                                 gfp_t flags)
@@ -612,12 +612,11 @@ static void destroy_gre_conntrack(struct nf_conn *ct)
 #endif
 }
 
-static void
-destroy_conntrack(struct nf_conntrack *nfct)
+void nf_ct_destroy(struct nf_conntrack *nfct)
 {
        struct nf_conn *ct = (struct nf_conn *)nfct;
 
-       pr_debug("destroy_conntrack(%p)\n", ct);
+       pr_debug("%s(%p)\n", __func__, ct);
        WARN_ON(refcount_read(&nfct->use) != 0);
 
        if (unlikely(nf_ct_is_template(ct))) {
@@ -643,9 +642,10 @@ destroy_conntrack(struct nf_conntrack *nfct)
        if (ct->master)
                nf_ct_put(ct->master);
 
-       pr_debug("destroy_conntrack: returning ct=%p to slab\n", ct);
+       pr_debug("%s: returning ct=%p to slab\n", __func__, ct);
        nf_conntrack_free(ct);
 }
+EXPORT_SYMBOL(nf_ct_destroy);
 
 static void nf_ct_delete_from_lists(struct nf_conn *ct)
 {
@@ -2771,7 +2771,7 @@ err_cachep:
 
 static const struct nf_ct_hook nf_conntrack_hook = {
        .update         = nf_conntrack_update,
-       .destroy        = destroy_conntrack,
+       .destroy        = nf_ct_destroy,
        .get_tuple_skb  = nf_conntrack_get_tuple_skb,
        .attach         = nf_conntrack_attach,
 };