Merge branch 'inet-frags-followup'

Eric Dumazet says:

====================
inet: frags: followup to 'inet-frags-avoid-possible-races-at-netns-dismantle'

Latest patch series ('inet-frags-avoid-possible-races-at-netns-dismantle')
brought another syzbot report shown in the third patch changelog.

While fixing the issue, I had to call inet_frags_fini() later
in IPv6 and ilowpan.

Also I believe a completion is needed to ensure proper dismantle
at module removal.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_frag.h

@@ -3,6 +3,7 @@
 #define __NET_FRAG_H__
 
 #include <linux/rhashtable-types.h>
+#include <linux/completion.h>
 
 /* Per netns frag queues directory */
 struct fqdir {
@@ -104,30 +105,14 @@ struct inet_frags {
 	struct kmem_cache	*frags_cachep;
 	const char		*frags_cache_name;
 	struct rhashtable_params rhash_params;
+	refcount_t		refcnt;
+	struct completion	completion;
 };
 
 int inet_frags_init(struct inet_frags *);
 void inet_frags_fini(struct inet_frags *);
 
-static inline int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f,
-			     struct net *net)
-{
-	struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
-	int res;
-
-	if (!fqdir)
-		return -ENOMEM;
-	fqdir->f = f;
-	fqdir->net = net;
-	res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
-	if (res < 0) {
-		kfree(fqdir);
-		return res;
-	}
-	*fqdirp = fqdir;
-	return 0;
-}
-
+int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net);
 void fqdir_exit(struct fqdir *fqdir);
 
 void inet_frag_kill(struct inet_frag_queue *q);

net/ieee802154/6lowpan/reassembly.c

@@ -540,7 +540,7 @@ err_sysctl:
 
 void lowpan_net_frag_exit(void)
 {
-	inet_frags_fini(&lowpan_frags);
 	lowpan_frags_sysctl_unregister();
 	unregister_pernet_subsys(&lowpan_frags_ops);
+	inet_frags_fini(&lowpan_frags);
 }

net/ipv4/inet_fragment.c

@@ -110,14 +110,18 @@ int inet_frags_init(struct inet_frags *f)
 	if (!f->frags_cachep)
 		return -ENOMEM;
 
+	refcount_set(&f->refcnt, 1);
+	init_completion(&f->completion);
 	return 0;
 }
 EXPORT_SYMBOL(inet_frags_init);
 
 void inet_frags_fini(struct inet_frags *f)
 {
-	/* We must wait that all inet_frag_destroy_rcu() have completed. */
-	rcu_barrier();
+	if (refcount_dec_and_test(&f->refcnt))
+		complete(&f->completion);
+
+	wait_for_completion(&f->completion);
 
 	kmem_cache_destroy(f->frags_cachep);
 	f->frags_cachep = NULL;
@@ -149,11 +153,42 @@ static void fqdir_rwork_fn(struct work_struct *work)
 {
 	struct fqdir *fqdir = container_of(to_rcu_work(work),
 					   struct fqdir, destroy_rwork);
+	struct inet_frags *f = fqdir->f;
 
 	rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL);
+
+	/* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
+	 * have completed, since they need to dereference fqdir.
+	 * Would it not be nice to have kfree_rcu_barrier() ? :)
+	 */
+	rcu_barrier();
+
+	if (refcount_dec_and_test(&f->refcnt))
+		complete(&f->completion);
+
 	kfree(fqdir);
 }
 
+int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
+{
+	struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
+	int res;
+
+	if (!fqdir)
+		return -ENOMEM;
+	fqdir->f = f;
+	fqdir->net = net;
+	res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
+	if (res < 0) {
+		kfree(fqdir);
+		return res;
+	}
+	refcount_inc(&f->refcnt);
+	*fqdirp = fqdir;
+	return 0;
+}
+EXPORT_SYMBOL(fqdir_init);
+
 void fqdir_exit(struct fqdir *fqdir)
 {
 	fqdir->high_thresh = 0; /* prevent creation of new frags */

net/ipv6/reassembly.c

@@ -583,8 +583,8 @@ err_protocol:
 
 void ipv6_frag_exit(void)
 {
-	inet_frags_fini(&ip6_frags);
 	ip6_frags_sysctl_unregister();
 	unregister_pernet_subsys(&ip6_frags_ops);
 	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
+	inet_frags_fini(&ip6_frags);
 }