net neigh: RCU conversion of neigh hash table

David

This is the first step for RCU conversion of neigh code.

Next patches will convert hash_buckets[] and "struct neighbour" to RCU
protected objects.

Thanks

[PATCH net-next] net neigh: RCU conversion of neigh hash table

Instead of storing hash_buckets, hash_mask and hash_rnd in "struct
neigh_table", a new structure is defined :

struct neigh_hash_table {
       struct neighbour        **hash_buckets;
       unsigned int            hash_mask;
       __u32                   hash_rnd;
       struct rcu_head         rcu;
};

And "struct neigh_table" has an RCU protected pointer to such a
neigh_hash_table.

This means the signature of (*hash)() function changed: We need to add a
third parameter with the actual hash_rnd value, since this is not
anymore a neigh_table field.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 137 insertions, 82 deletions

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index d6996e072a41..dd8920e4f508 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -131,14 +131,17 @@ static int neigh_forced_gc(struct neigh_table *tbl)
 {
         int shrunk = 0;
         int i;
+        struct neigh_hash_table *nht;
 
         NEIGH_CACHE_STAT_INC(tbl, forced_gc_runs);
 
         write_lock_bh(&tbl->lock);
-        for (i = 0; i <= tbl->hash_mask; i++) {
+        nht = rcu_dereference_protected(tbl->nht,
+                                        lockdep_is_held(&tbl->lock));
+        for (i = 0; i <= nht->hash_mask; i++) {
                 struct neighbour *n, **np;
 
-                np = &tbl->hash_buckets[i];
+                np = &nht->hash_buckets[i];
                 while ((n = *np) != NULL) {
                         /* Neighbour record may be discarded if:
                          * - nobody refers to it.
@@ -199,9 +202,13 @@ static void pneigh_queue_purge(struct sk_buff_head *list)
 static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev)
 {
         int i;
+        struct neigh_hash_table *nht;
 
-        for (i = 0; i <= tbl->hash_mask; i++) {
-                struct neighbour *n, **np = &tbl->hash_buckets[i];
+        nht = rcu_dereference_protected(tbl->nht,
+                                        lockdep_is_held(&tbl->lock));
+
+        for (i = 0; i <= nht->hash_mask; i++) {
+                struct neighbour *n, **np = &nht->hash_buckets[i];
 
                 while ((n = *np) != NULL) {
                         if (dev && n->dev != dev) {
@@ -297,64 +304,81 @@ out_entries:
         goto out;
 }
 
-static struct neighbour **neigh_hash_alloc(unsigned int entries)
+static struct neigh_hash_table *neigh_hash_alloc(unsigned int entries)
 {
-        unsigned long size = entries * sizeof(struct neighbour *);
-        struct neighbour **ret;
+        size_t size = entries * sizeof(struct neighbour *);
+        struct neigh_hash_table *ret;
+        struct neighbour **buckets;
 
-        if (size <= PAGE_SIZE) {
-                ret = kzalloc(size, GFP_ATOMIC);
-        } else {
-                ret = (struct neighbour **)
-                      __get_free_pages(GFP_ATOMIC|__GFP_ZERO, get_order(size));
+        ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
+        if (!ret)
+                return NULL;
+        if (size <= PAGE_SIZE)
+                buckets = kzalloc(size, GFP_ATOMIC);
+        else
+                buckets = (struct neighbour **)
+                          __get_free_pages(GFP_ATOMIC | __GFP_ZERO,
+                                           get_order(size));
+        if (!buckets) {
+                kfree(ret);
+                return NULL;
         }
+        ret->hash_buckets = buckets;
+        ret->hash_mask = entries - 1;
+        get_random_bytes(&ret->hash_rnd, sizeof(ret->hash_rnd));
         return ret;
 }
 
-static void neigh_hash_free(struct neighbour **hash, unsigned int entries)
+static void neigh_hash_free_rcu(struct rcu_head *head)
 {
-        unsigned long size = entries * sizeof(struct neighbour *);
+        struct neigh_hash_table *nht = container_of(head,
+                                                    struct neigh_hash_table,
+                                                    rcu);
+        size_t size = (nht->hash_mask + 1) * sizeof(struct neighbour *);
+        struct neighbour **buckets = nht->hash_buckets;
 
         if (size <= PAGE_SIZE)
-                kfree(hash);
+                kfree(buckets);
         else
-                free_pages((unsigned long)hash, get_order(size));
+                free_pages((unsigned long)buckets, get_order(size));
+        kfree(nht);
 }
 
-static void neigh_hash_grow(struct neigh_table *tbl, unsigned long new_entries)
+static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl,
+                                                unsigned long new_entries)
 {
-        struct neighbour **new_hash, **old_hash;
-        unsigned int i, new_hash_mask, old_entries;
+        unsigned int i, hash;
+        struct neigh_hash_table *new_nht, *old_nht;
 
         NEIGH_CACHE_STAT_INC(tbl, hash_grows);
 
         BUG_ON(!is_power_of_2(new_entries));
-        new_hash = neigh_hash_alloc(new_entries);
-        if (!new_hash)
-                return;
+        old_nht = rcu_dereference_protected(tbl->nht,
+                                            lockdep_is_held(&tbl->lock));
+        new_nht = neigh_hash_alloc(new_entries);
+        if (!new_nht)
+                return old_nht;
 
-        old_entries = tbl->hash_mask + 1;
-        new_hash_mask = new_entries - 1;
-        old_hash = tbl->hash_buckets;
-
-        get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
-        for (i = 0; i < old_entries; i++) {
+        for (i = 0; i <= old_nht->hash_mask; i++) {
                 struct neighbour *n, *next;
 
-                for (n = old_hash[i]; n; n = next) {
-                        unsigned int hash_val = tbl->hash(n->primary_key, n->dev);
+                for (n = old_nht->hash_buckets[i];
+                     n != NULL;
+                     n = next) {
+                        hash = tbl->hash(n->primary_key, n->dev,
+                                         new_nht->hash_rnd);
 
-                        hash_val &= new_hash_mask;
+                        hash &= new_nht->hash_mask;
                         next = n->next;
 
-                        n->next = new_hash[hash_val];
-                        new_hash[hash_val] = n;
+                        n->next = new_nht->hash_buckets[hash];
+                        new_nht->hash_buckets[hash] = n;
                 }
         }
-        tbl->hash_buckets = new_hash;
-        tbl->hash_mask = new_hash_mask;
 
-        neigh_hash_free(old_hash, old_entries);
+        rcu_assign_pointer(tbl->nht, new_nht);
+        call_rcu(&old_nht->rcu, neigh_hash_free_rcu);
+        return new_nht;
 }
 
 struct neighbour *neigh_lookup(struct neigh_table *tbl, const void *pkey,
@@ -363,19 +387,23 @@ struct neighbour *neigh_lookup(struct neigh_table *tbl, const void *pkey,
         struct neighbour *n;
         int key_len = tbl->key_len;
         u32 hash_val;
+        struct neigh_hash_table *nht;
 
         NEIGH_CACHE_STAT_INC(tbl, lookups);
 
-        read_lock_bh(&tbl->lock);
-        hash_val = tbl->hash(pkey, dev);
-        for (n = tbl->hash_buckets[hash_val & tbl->hash_mask]; n; n = n->next) {
+        rcu_read_lock_bh();
+        nht = rcu_dereference_bh(tbl->nht);
+        hash_val = tbl->hash(pkey, dev, nht->hash_rnd) & nht->hash_mask;
+        read_lock(&tbl->lock);
+        for (n = nht->hash_buckets[hash_val]; n; n = n->next) {
                 if (dev == n->dev && !memcmp(n->primary_key, pkey, key_len)) {
                         neigh_hold(n);
                         NEIGH_CACHE_STAT_INC(tbl, hits);
                         break;
                 }
         }
-        read_unlock_bh(&tbl->lock);
+        read_unlock(&tbl->lock);
+        rcu_read_unlock_bh();
         return n;
 }
 EXPORT_SYMBOL(neigh_lookup);
@@ -386,12 +414,15 @@ struct neighbour *neigh_lookup_nodev(struct neigh_table *tbl, struct net *net,
         struct neighbour *n;
         int key_len = tbl->key_len;
         u32 hash_val;
+        struct neigh_hash_table *nht;
 
         NEIGH_CACHE_STAT_INC(tbl, lookups);
 
-        read_lock_bh(&tbl->lock);
-        hash_val = tbl->hash(pkey, NULL);
-        for (n = tbl->hash_buckets[hash_val & tbl->hash_mask]; n; n = n->next) {
+        rcu_read_lock_bh();
+        nht = rcu_dereference_bh(tbl->nht);
+        hash_val = tbl->hash(pkey, NULL, nht->hash_rnd) & nht->hash_mask;
+        read_lock(&tbl->lock);
+        for (n = nht->hash_buckets[hash_val]; n; n = n->next) {
                 if (!memcmp(n->primary_key, pkey, key_len) &&
                     net_eq(dev_net(n->dev), net)) {
                         neigh_hold(n);
@@ -399,7 +430,8 @@ struct neighbour *neigh_lookup_nodev(struct neigh_table *tbl, struct net *net,
                         break;
                 }
         }
-        read_unlock_bh(&tbl->lock);
+        read_unlock(&tbl->lock);
+        rcu_read_unlock_bh();
         return n;
 }
 EXPORT_SYMBOL(neigh_lookup_nodev);
@@ -411,6 +443,7 @@ struct neighbour *neigh_create(struct neigh_table *tbl, const void *pkey,
         int key_len = tbl->key_len;
         int error;
         struct neighbour *n1, *rc, *n = neigh_alloc(tbl);
+        struct neigh_hash_table *nht;
 
         if (!n) {
                 rc = ERR_PTR(-ENOBUFS);
@@ -437,18 +470,20 @@ struct neighbour *neigh_create(struct neigh_table *tbl, const void *pkey,
         n->confirmed = jiffies - (n->parms->base_reachable_time << 1);
 
         write_lock_bh(&tbl->lock);
+        nht = rcu_dereference_protected(tbl->nht,
+                                        lockdep_is_held(&tbl->lock));
 
-        if (atomic_read(&tbl->entries) > (tbl->hash_mask + 1))
-                neigh_hash_grow(tbl, (tbl->hash_mask + 1) << 1);
+        if (atomic_read(&tbl->entries) > (nht->hash_mask + 1))
+                nht = neigh_hash_grow(tbl, (nht->hash_mask + 1) << 1);
 
-        hash_val = tbl->hash(pkey, dev) & tbl->hash_mask;
+        hash_val = tbl->hash(pkey, dev, nht->hash_rnd) & nht->hash_mask;
 
         if (n->parms->dead) {
                 rc = ERR_PTR(-EINVAL);
                 goto out_tbl_unlock;
         }
 
-        for (n1 = tbl->hash_buckets[hash_val]; n1; n1 = n1->next) {
+        for (n1 = nht->hash_buckets[hash_val]; n1; n1 = n1->next) {
                 if (dev == n1->dev && !memcmp(n1->primary_key, pkey, key_len)) {
                         neigh_hold(n1);
                         rc = n1;
@@ -456,8 +491,8 @@ struct neighbour *neigh_create(struct neigh_table *tbl, const void *pkey,
                 }
         }
 
-        n->next = tbl->hash_buckets[hash_val];
-        tbl->hash_buckets[hash_val] = n;
+        n->next = nht->hash_buckets[hash_val];
+        nht->hash_buckets[hash_val] = n;
         n->dead = 0;
         neigh_hold(n);
         write_unlock_bh(&tbl->lock);
@@ -698,10 +733,13 @@ static void neigh_periodic_work(struct work_struct *work)
         struct neigh_table *tbl = container_of(work, struct neigh_table, gc_work.work);
         struct neighbour *n, **np;
         unsigned int i;
+        struct neigh_hash_table *nht;
 
         NEIGH_CACHE_STAT_INC(tbl, periodic_gc_runs);
 
         write_lock_bh(&tbl->lock);
+        nht = rcu_dereference_protected(tbl->nht,
+                                        lockdep_is_held(&tbl->lock));
 
         /*
          *      periodically recompute ReachableTime from random function
@@ -715,8 +753,8 @@ static void neigh_periodic_work(struct work_struct *work)
                                 neigh_rand_reach_time(p->base_reachable_time);
         }
 
-        for (i = 0 ; i <= tbl->hash_mask; i++) {
-                np = &tbl->hash_buckets[i];
+        for (i = 0 ; i <= nht->hash_mask; i++) {
+                np = &nht->hash_buckets[i];
 
                 while ((n = *np) != NULL) {
                         unsigned int state;
@@ -1438,17 +1476,14 @@ void neigh_table_init_no_netlink(struct neigh_table *tbl)
                 panic("cannot create neighbour proc dir entry");
 #endif
 
-        tbl->hash_mask = 1;
-        tbl->hash_buckets = neigh_hash_alloc(tbl->hash_mask + 1);
+        tbl->nht = neigh_hash_alloc(8);
 
         phsize = (PNEIGH_HASHMASK + 1) * sizeof(struct pneigh_entry *);
         tbl->phash_buckets = kzalloc(phsize, GFP_KERNEL);
 
-        if (!tbl->hash_buckets || !tbl->phash_buckets)
+        if (!tbl->nht || !tbl->phash_buckets)
                 panic("cannot allocate neighbour cache hashes");
 
-        get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
-
         rwlock_init(&tbl->lock);
         INIT_DELAYED_WORK_DEFERRABLE(&tbl->gc_work, neigh_periodic_work);
         schedule_delayed_work(&tbl->gc_work, tbl->parms.reachable_time);
@@ -1504,8 +1539,8 @@ int neigh_table_clear(struct neigh_table *tbl)
         }
         write_unlock(&neigh_tbl_lock);
 
-        neigh_hash_free(tbl->hash_buckets, tbl->hash_mask + 1);
-        tbl->hash_buckets = NULL;
+        call_rcu(&tbl->nht->rcu, neigh_hash_free_rcu);
+        tbl->nht = NULL;
 
         kfree(tbl->phash_buckets);
         tbl->phash_buckets = NULL;
@@ -1745,18 +1780,22 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl,
                 unsigned long now = jiffies;
                 unsigned int flush_delta = now - tbl->last_flush;
                 unsigned int rand_delta = now - tbl->last_rand;
-
+                struct neigh_hash_table *nht;
                 struct ndt_config ndc = {
                         .ndtc_key_len           = tbl->key_len,
                         .ndtc_entry_size        = tbl->entry_size,
                         .ndtc_entries           = atomic_read(&tbl->entries),
                         .ndtc_last_flush        = jiffies_to_msecs(flush_delta),
                         .ndtc_last_rand         = jiffies_to_msecs(rand_delta),
-                        .ndtc_hash_rnd          = tbl->hash_rnd,
-                        .ndtc_hash_mask         = tbl->hash_mask,
                         .ndtc_proxy_qlen        = tbl->proxy_queue.qlen,
                 };
 
+                rcu_read_lock_bh();
+                nht = rcu_dereference_bh(tbl->nht);
+                ndc.ndtc_hash_rnd = nht->hash_rnd;
+                ndc.ndtc_hash_mask = nht->hash_mask;
+                rcu_read_unlock_bh();
+
                 NLA_PUT(skb, NDTA_CONFIG, sizeof(ndc), &ndc);
         }
 
@@ -2088,14 +2127,18 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
         struct neighbour *n;
         int rc, h, s_h = cb->args[1];
         int idx, s_idx = idx = cb->args[2];
+        struct neigh_hash_table *nht;
 
-        read_lock_bh(&tbl->lock);
-        for (h = 0; h <= tbl->hash_mask; h++) {
+        rcu_read_lock_bh();
+        nht = rcu_dereference_bh(tbl->nht);
+
+        read_lock(&tbl->lock);
+        for (h = 0; h <= nht->hash_mask; h++) {
                 if (h < s_h)
                         continue;
                 if (h > s_h)
                         s_idx = 0;
-                for (n = tbl->hash_buckets[h], idx = 0; n; n = n->next) {
+                for (n = nht->hash_buckets[h], idx = 0; n; n = n->next) {
                         if (!net_eq(dev_net(n->dev), net))
                                 continue;
                         if (idx < s_idx)
@@ -2104,7 +2147,6 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
                                             cb->nlh->nlmsg_seq,
                                             RTM_NEWNEIGH,
                                             NLM_F_MULTI) <= 0) {
-                                read_unlock_bh(&tbl->lock);
                                 rc = -1;
                                 goto out;
                         }
@@ -2112,9 +2154,10 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
                         idx++;
                 }
         }
-        read_unlock_bh(&tbl->lock);
         rc = skb->len;
 out:
+        read_unlock(&tbl->lock);
+        rcu_read_unlock_bh();
         cb->args[1] = h;
         cb->args[2] = idx;
         return rc;
@@ -2147,15 +2190,20 @@ static int neigh_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 void neigh_for_each(struct neigh_table *tbl, void (*cb)(struct neighbour *, void *), void *cookie)
 {
         int chain;
+        struct neigh_hash_table *nht;
 
-        read_lock_bh(&tbl->lock);
-        for (chain = 0; chain <= tbl->hash_mask; chain++) {
+        rcu_read_lock_bh();
+        nht = rcu_dereference_bh(tbl->nht);
+
+        read_lock(&tbl->lock);
+        for (chain = 0; chain <= nht->hash_mask; chain++) {
                 struct neighbour *n;
 
-                for (n = tbl->hash_buckets[chain]; n; n = n->next)
+                for (n = nht->hash_buckets[chain]; n; n = n->next)
                         cb(n, cookie);
         }
-        read_unlock_bh(&tbl->lock);
+        read_unlock(&tbl->lock);
+        rcu_read_unlock_bh();
 }
 EXPORT_SYMBOL(neigh_for_each);
 
@@ -2164,11 +2212,14 @@ void __neigh_for_each_release(struct neigh_table *tbl,
                               int (*cb)(struct neighbour *))
 {
         int chain;
+        struct neigh_hash_table *nht;
 
-        for (chain = 0; chain <= tbl->hash_mask; chain++) {
+        nht = rcu_dereference_protected(tbl->nht,
+                                        lockdep_is_held(&tbl->lock));
+        for (chain = 0; chain <= nht->hash_mask; chain++) {
                 struct neighbour *n, **np;
 
-                np = &tbl->hash_buckets[chain];
+                np = &nht->hash_buckets[chain];
                 while ((n = *np) != NULL) {
                         int release;
 
@@ -2193,13 +2244,13 @@ static struct neighbour *neigh_get_first(struct seq_file *seq)
 {
         struct neigh_seq_state *state = seq->private;
         struct net *net = seq_file_net(seq);
-        struct neigh_table *tbl = state->tbl;
+        struct neigh_hash_table *nht = state->nht;
         struct neighbour *n = NULL;
         int bucket = state->bucket;
 
         state->flags &= ~NEIGH_SEQ_IS_PNEIGH;
-        for (bucket = 0; bucket <= tbl->hash_mask; bucket++) {
-                n = tbl->hash_buckets[bucket];
+        for (bucket = 0; bucket <= nht->hash_mask; bucket++) {
+                n = nht->hash_buckets[bucket];
 
                 while (n) {
                         if (!net_eq(dev_net(n->dev), net))
@@ -2234,7 +2285,7 @@ static struct neighbour *neigh_get_next(struct seq_file *seq,
 {
         struct neigh_seq_state *state = seq->private;
         struct net *net = seq_file_net(seq);
-        struct neigh_table *tbl = state->tbl;
+        struct neigh_hash_table *nht = state->nht;
 
         if (state->neigh_sub_iter) {
                 void *v = state->neigh_sub_iter(state, n, pos);
@@ -2265,10 +2316,10 @@ static struct neighbour *neigh_get_next(struct seq_file *seq,
                 if (n)
                         break;
 
-                if (++state->bucket > tbl->hash_mask)
+                if (++state->bucket > nht->hash_mask)
                         break;
 
-                n = tbl->hash_buckets[state->bucket];
+                n = nht->hash_buckets[state->bucket];
         }
 
         if (n && pos)
@@ -2367,6 +2418,7 @@ static void *neigh_get_idx_any(struct seq_file *seq, loff_t *pos)
 
 void *neigh_seq_start(struct seq_file *seq, loff_t *pos, struct neigh_table *tbl, unsigned int neigh_seq_flags)
         __acquires(tbl->lock)
+        __acquires(rcu_bh)
 {
         struct neigh_seq_state *state = seq->private;
 
@@ -2374,8 +2426,9 @@ void *neigh_seq_start(struct seq_file *seq, loff_t *pos, struct neigh_table *tbl
         state->bucket = 0;
         state->flags = (neigh_seq_flags & ~NEIGH_SEQ_IS_PNEIGH);
 
-        read_lock_bh(&tbl->lock);
-
+        rcu_read_lock_bh();
+        state->nht = rcu_dereference_bh(tbl->nht);
+        read_lock(&tbl->lock);
         return *pos ? neigh_get_idx_any(seq, pos) : SEQ_START_TOKEN;
 }
 EXPORT_SYMBOL(neigh_seq_start);
@@ -2409,11 +2462,13 @@ EXPORT_SYMBOL(neigh_seq_next);
 
 void neigh_seq_stop(struct seq_file *seq, void *v)
         __releases(tbl->lock)
+        __releases(rcu_bh)
 {
         struct neigh_seq_state *state = seq->private;
         struct neigh_table *tbl = state->tbl;
 
-        read_unlock_bh(&tbl->lock);
+        read_unlock(&tbl->lock);
+        rcu_read_unlock_bh();
 }
 EXPORT_SYMBOL(neigh_seq_stop);