2 files changed, 55 insertions, 34 deletions

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 58d4c38534f6..62b1f73749dc 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -68,8 +68,7 @@ static void inet_frag_secret_rebuild(struct inet_frags *f)
 {
 	int i;
 
-	/* Per bucket lock NOT needed here, due to write lock protection */
-	write_lock_bh(&f->lock);
+	write_seqlock_bh(&f->rnd_seqlock);
 
 	if (!inet_frag_may_rebuild(f))
 		goto out;
@@ -82,6 +81,8 @@ static void inet_frag_secret_rebuild(struct inet_frags *f)
 		struct hlist_node *n;
 
 		hb = &f->hash[i];
+		spin_lock(&hb->chain_lock);
+
 		hlist_for_each_entry_safe(q, n, &hb->chain, list) {
 			unsigned int hval = inet_frag_hashfn(f, q);
 
@@ -92,15 +93,28 @@ static void inet_frag_secret_rebuild(struct inet_frags *f)
 
 				/* Relink to new hash chain. */
 				hb_dest = &f->hash[hval];
+
+				/* This is the only place where we take
+				 * another chain_lock while already holding
+				 * one.  As this will not run concurrently,
+				 * we cannot deadlock on hb_dest lock below, if its
+				 * already locked it will be released soon since
+				 * other caller cannot be waiting for hb lock
+				 * that we've taken above.
+				 */
+				spin_lock_nested(&hb_dest->chain_lock,
+						 SINGLE_DEPTH_NESTING);
 				hlist_add_head(&q->list, &hb_dest->chain);
+				spin_unlock(&hb_dest->chain_lock);
 			}
 		}
+		spin_unlock(&hb->chain_lock);
 	}
 
 	f->rebuild = false;
 	f->last_rebuild_jiffies = jiffies;
 out:
-	write_unlock_bh(&f->lock);
+	write_sequnlock_bh(&f->rnd_seqlock);
 }
 
 static bool inet_fragq_should_evict(const struct inet_frag_queue *q)
@@ -163,7 +177,7 @@ static void inet_frag_worker(struct work_struct *work)
 
 	BUILD_BUG_ON(INETFRAGS_EVICT_BUCKETS >= INETFRAGS_HASHSZ);
 
-	read_lock_bh(&f->lock);
+	local_bh_disable();
 
 	for (i = ACCESS_ONCE(f->next_bucket); budget; --budget) {
 		evicted += inet_evict_bucket(f, &f->hash[i]);
@@ -174,7 +188,8 @@ static void inet_frag_worker(struct work_struct *work)
 
 	f->next_bucket = i;
 
-	read_unlock_bh(&f->lock);
+	local_bh_enable();
+
 	if (f->rebuild && inet_frag_may_rebuild(f))
 		inet_frag_secret_rebuild(f);
 }
@@ -197,7 +212,8 @@ void inet_frags_init(struct inet_frags *f)
 		spin_lock_init(&hb->chain_lock);
 		INIT_HLIST_HEAD(&hb->chain);
 	}
-	rwlock_init(&f->lock);
+
+	seqlock_init(&f->rnd_seqlock);
 	f->last_rebuild_jiffies = 0;
 }
 EXPORT_SYMBOL(inet_frags_init);
@@ -216,35 +232,56 @@ EXPORT_SYMBOL(inet_frags_fini);
 
 void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f)
 {
+	unsigned int seq;
 	int i;
 
 	nf->low_thresh = 0;
+	local_bh_disable();
 
-	read_lock_bh(&f->lock);
+evict_again:
+	seq = read_seqbegin(&f->rnd_seqlock);
 
 	for (i = 0; i < INETFRAGS_HASHSZ ; i++)
 		inet_evict_bucket(f, &f->hash[i]);
 
-	read_unlock_bh(&f->lock);
+	if (read_seqretry(&f->rnd_seqlock, seq))
+		goto evict_again;
+
+	local_bh_enable();
 
 	percpu_counter_destroy(&nf->mem);
 }
 EXPORT_SYMBOL(inet_frags_exit_net);
 
-static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
+static struct inet_frag_bucket *
+get_frag_bucket_locked(struct inet_frag_queue *fq, struct inet_frags *f)
+__acquires(hb->chain_lock)
 {
 	struct inet_frag_bucket *hb;
-	unsigned int hash;
+	unsigned int seq, hash;
+
+ restart:
+	seq = read_seqbegin(&f->rnd_seqlock);
 
-	read_lock(&f->lock);
 	hash = inet_frag_hashfn(f, fq);
 	hb = &f->hash[hash];
 
 	spin_lock(&hb->chain_lock);
+	if (read_seqretry(&f->rnd_seqlock, seq)) {
+		spin_unlock(&hb->chain_lock);
+		goto restart;
+	}
+
+	return hb;
+}
+
+static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
+{
+	struct inet_frag_bucket *hb;
+
+	hb = get_frag_bucket_locked(fq, f);
 	hlist_del(&fq->list);
 	spin_unlock(&hb->chain_lock);
-
-	read_unlock(&f->lock);
 }
 
 void inet_frag_kill(struct inet_frag_queue *fq, struct inet_frags *f)
@@ -300,30 +337,18 @@ static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
 		struct inet_frag_queue *qp_in, struct inet_frags *f,
 		void *arg)
 {
-	struct inet_frag_bucket *hb;
+	struct inet_frag_bucket *hb = get_frag_bucket_locked(qp_in, f);
 	struct inet_frag_queue *qp;
-	unsigned int hash;
-
-	read_lock(&f->lock); /* Protects against hash rebuild */
-	/*
-	 * While we stayed w/o the lock other CPU could update
-	 * the rnd seed, so we need to re-calculate the hash
-	 * chain. Fortunatelly the qp_in can be used to get one.
-	 */
-	hash = inet_frag_hashfn(f, qp_in);
-	hb = &f->hash[hash];
-	spin_lock(&hb->chain_lock);
 
 #ifdef CONFIG_SMP
 	/* With SMP race we have to recheck hash table, because
-	 * such entry could be created on other cpu, while we
-	 * released the hash bucket lock.
+	 * such entry could have been created on other cpu before
+	 * we acquired hash bucket lock.
 	 */
 	hlist_for_each_entry(qp, &hb->chain, list) {
 		if (qp->net == nf && f->match(qp, arg)) {
 			atomic_inc(&qp->refcnt);
 			spin_unlock(&hb->chain_lock);
-			read_unlock(&f->lock);
 			qp_in->last_in |= INET_FRAG_COMPLETE;
 			inet_frag_put(qp_in, f);
 			return qp;
@@ -338,7 +363,6 @@ static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
 	hlist_add_head(&qp->list, &hb->chain);
 
 	spin_unlock(&hb->chain_lock);
-	read_unlock(&f->lock);
 
 	return qp;
 }
@@ -382,7 +406,6 @@ static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
 
 struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
 		struct inet_frags *f, void *key, unsigned int hash)
-	__releases(&f->lock)
 {
 	struct inet_frag_bucket *hb;
 	struct inet_frag_queue *q;
@@ -399,19 +422,18 @@ struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
 		if (q->net == nf && f->match(q, key)) {
 			atomic_inc(&q->refcnt);
 			spin_unlock(&hb->chain_lock);
-			read_unlock(&f->lock);
 			return q;
 		}
 		depth++;
 	}
 	spin_unlock(&hb->chain_lock);
-	read_unlock(&f->lock);
 
 	if (depth <= INETFRAGS_MAXDEPTH)
 		return inet_frag_create(nf, f, key);
 
 	if (inet_frag_may_rebuild(f)) {
-		f->rebuild = true;
+		if (!f->rebuild)
+			f->rebuild = true;
 		inet_frag_schedule_worker(f);
 	}
 
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 44e591a7e03f..ccee68dffd6e 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -244,7 +244,6 @@ static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
 	arg.iph = iph;
 	arg.user = user;
 
-	read_lock(&ip4_frags.lock);
 	hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
 
 	q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);