6 files changed, 62 insertions, 44 deletions

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index d9cc5bb64854..6f4930a0b660 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -53,11 +53,6 @@ struct inet_frag_bucket {
 
 struct inet_frags {
         struct inet_frag_bucket hash[INETFRAGS_HASHSZ];
-        /* This rwlock is a global lock (seperate per IPv4, IPv6 and
-         * netfilter). Important to keep this on a seperate cacheline.
-         * Its primarily a rebuild protection rwlock.
-         */
-        rwlock_t                lock ____cacheline_aligned_in_smp;
 
         struct work_struct      frags_work;
         unsigned int next_bucket;
@@ -66,8 +61,12 @@ struct inet_frags {
 
         /* The first call to hashfn is responsible to initialize
          * rnd. This is best done with net_get_random_once.
+         *
+         * rnd_seqlock is used to let hash insertion detect
+         * when it needs to re-lookup the hash chain to use.
          */
         u32                     rnd;
+        seqlock_t               rnd_seqlock;
         int                     qsize;
 
         unsigned int            (*hashfn)(const struct inet_frag_queue *);
@@ -89,8 +88,8 @@ void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f);
 void inet_frag_kill(struct inet_frag_queue *q, struct inet_frags *f);
 void inet_frag_destroy(struct inet_frag_queue *q, struct inet_frags *f);
 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_frags *f, void *key, unsigned int hash);
+
 void inet_frag_maybe_warn_overflow(struct inet_frag_queue *q,
                                    const char *prefix);
 
diff --git a/net/ieee802154/reassembly.c b/net/ieee802154/reassembly.c
index 20d219682d84..8da635d92a58 100644
--- a/net/ieee802154/reassembly.c
+++ b/net/ieee802154/reassembly.c
@@ -124,7 +124,6 @@ fq_find(struct net *net, const struct lowpan_frag_info *frag_info,
         arg.src = src;
         arg.dst = dst;
 
-        read_lock(&lowpan_frags.lock);
         hash = lowpan_hash_frag(frag_info->d_tag, frag_info->d_size, src, dst);
 
         q = inet_frag_find(&ieee802154_lowpan->frags,
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);
diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 3b3ef9774cc2..4d9da1e35f8c 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -193,7 +193,7 @@ static inline struct frag_queue *fq_find(struct net *net, __be32 id,
         arg.dst = dst;
         arg.ecn = ecn;
 
-        read_lock_bh(&nf_frags.lock);
+        local_bh_disable();
         hash = nf_hash_frag(id, src, dst);
 
         q = inet_frag_find(&net->nf_frag.frags, &nf_frags, &arg, hash);
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 987fea46b915..57a9707b2032 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -190,7 +190,6 @@ fq_find(struct net *net, __be32 id, const struct in6_addr *src,
         arg.dst = dst;
         arg.ecn = ecn;
 
-        read_lock(&ip6_frags.lock);
         hash = inet6_hash_frag(id, src, dst);
 
         q = inet_frag_find(&net->ipv6.frags, &ip6_frags, &arg, hash);