neigh: RCU conversion of struct neighbour

This is the second step for neighbour RCU conversion.

(first was commit d6bf7817 : RCU conversion of neigh hash table)

neigh_lookup() becomes lockless, but still take a reference on found
neighbour. (no more read_lock()/read_unlock() on tbl->lock)

struct neighbour gets an additional rcu_head field and is freed after an
RCU grace period.

Future work would need to eventually not take a reference on neighbour
for temporary dst (DST_NOCACHE), but this would need dst->_neighbour to
use a noref bit like we did for skb->_dst.

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

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 37845da..a4538d5 100644 (file)
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -91,7 +91,7 @@ struct neigh_statistics {
 #define NEIGH_CACHE_STAT_INC(tbl, field) this_cpu_inc((tbl)->stats->field)
 
 struct neighbour {
-       struct neighbour        *next;
+       struct neighbour __rcu  *next;
        struct neigh_table      *tbl;
        struct neigh_parms      *parms;
        struct net_device       *dev;
@@ -111,6 +111,7 @@ struct neighbour {
        struct sk_buff_head     arp_queue;
        struct timer_list       timer;
        const struct neigh_ops  *ops;
+       struct rcu_head         rcu;
        u8                      primary_key[0];
 };
 
@@ -139,7 +140,7 @@ struct pneigh_entry {
  */
 
 struct neigh_hash_table {
-       struct neighbour        **hash_buckets;
+       struct neighbour __rcu  **hash_buckets;
        unsigned int            hash_mask;
        __u32                   hash_rnd;
        struct rcu_head         rcu;

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index dd8920e..3ffafaa 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -139,10 +139,12 @@ static int neigh_forced_gc(struct neigh_table *tbl)
        nht = rcu_dereference_protected(tbl->nht,
                                        lockdep_is_held(&tbl->lock));
        for (i = 0; i <= nht->hash_mask; i++) {
-               struct neighbour *n, **np;
+               struct neighbour *n;
+               struct neighbour __rcu **np;
 
                np = &nht->hash_buckets[i];
-               while ((n = *np) != NULL) {
+               while ((n = rcu_dereference_protected(*np,
+                                       lockdep_is_held(&tbl->lock))) != NULL) {
                        /* Neighbour record may be discarded if:
                         * - nobody refers to it.
                         * - it is not permanent
@@ -150,7 +152,9 @@ static int neigh_forced_gc(struct neigh_table *tbl)
                        write_lock(&n->lock);
                        if (atomic_read(&n->refcnt) == 1 &&
                            !(n->nud_state & NUD_PERMANENT)) {
-                               *np     = n->next;
+                               rcu_assign_pointer(*np,
+                                       rcu_dereference_protected(n->next,
+                                                 lockdep_is_held(&tbl->lock)));
                                n->dead = 1;
                                shrunk  = 1;
                                write_unlock(&n->lock);
@@ -208,14 +212,18 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev)
                                        lockdep_is_held(&tbl->lock));
 
        for (i = 0; i <= nht->hash_mask; i++) {
-               struct neighbour *n, **np = &nht->hash_buckets[i];
+               struct neighbour *n;
+               struct neighbour __rcu **np = &nht->hash_buckets[i];
 
-               while ((n = *np) != NULL) {
+               while ((n = rcu_dereference_protected(*np,
+                                       lockdep_is_held(&tbl->lock))) != NULL) {
                        if (dev && n->dev != dev) {
                                np = &n->next;
                                continue;
                        }
-                       *np = n->next;
+                       rcu_assign_pointer(*np,
+                                  rcu_dereference_protected(n->next,
+                                               lockdep_is_held(&tbl->lock)));
                        write_lock(&n->lock);
                        neigh_del_timer(n);
                        n->dead = 1;
@@ -323,7 +331,7 @@ static struct neigh_hash_table *neigh_hash_alloc(unsigned int entries)
                kfree(ret);
                return NULL;
        }
-       ret->hash_buckets = buckets;
+       rcu_assign_pointer(ret->hash_buckets, buckets);
        ret->hash_mask = entries - 1;
        get_random_bytes(&ret->hash_rnd, sizeof(ret->hash_rnd));
        return ret;
@@ -362,17 +370,22 @@ static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl,
        for (i = 0; i <= old_nht->hash_mask; i++) {
                struct neighbour *n, *next;
 
-               for (n = old_nht->hash_buckets[i];
+               for (n = rcu_dereference_protected(old_nht->hash_buckets[i],
+                                                  lockdep_is_held(&tbl->lock));
                     n != NULL;
                     n = next) {
                        hash = tbl->hash(n->primary_key, n->dev,
                                         new_nht->hash_rnd);
 
                        hash &= new_nht->hash_mask;
-                       next = n->next;
-
-                       n->next = new_nht->hash_buckets[hash];
-                       new_nht->hash_buckets[hash] = n;
+                       next = rcu_dereference_protected(n->next,
+                                               lockdep_is_held(&tbl->lock));
+
+                       rcu_assign_pointer(n->next,
+                                          rcu_dereference_protected(
+                                               new_nht->hash_buckets[hash],
+                                               lockdep_is_held(&tbl->lock)));
+                       rcu_assign_pointer(new_nht->hash_buckets[hash], n);
                }
        }
 
@@ -394,15 +407,18 @@ struct neighbour *neigh_lookup(struct neigh_table *tbl, const void *pkey,
        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) {
+
+       for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
+            n != NULL;
+            n = rcu_dereference_bh(n->next)) {
                if (dev == n->dev && !memcmp(n->primary_key, pkey, key_len)) {
-                       neigh_hold(n);
+                       if (!atomic_inc_not_zero(&n->refcnt))
+                               n = NULL;
                        NEIGH_CACHE_STAT_INC(tbl, hits);
                        break;
                }
        }
-       read_unlock(&tbl->lock);
+
        rcu_read_unlock_bh();
        return n;
 }
@@ -421,16 +437,19 @@ struct neighbour *neigh_lookup_nodev(struct neigh_table *tbl, struct net *net,
        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) {
+
+       for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
+            n != NULL;
+            n = rcu_dereference_bh(n->next)) {
                if (!memcmp(n->primary_key, pkey, key_len) &&
                    net_eq(dev_net(n->dev), net)) {
-                       neigh_hold(n);
+                       if (!atomic_inc_not_zero(&n->refcnt))
+                               n = NULL;
                        NEIGH_CACHE_STAT_INC(tbl, hits);
                        break;
                }
        }
-       read_unlock(&tbl->lock);
+
        rcu_read_unlock_bh();
        return n;
 }
@@ -483,7 +502,11 @@ struct neighbour *neigh_create(struct neigh_table *tbl, const void *pkey,
                goto out_tbl_unlock;
        }
 
-       for (n1 = nht->hash_buckets[hash_val]; n1; n1 = n1->next) {
+       for (n1 = rcu_dereference_protected(nht->hash_buckets[hash_val],
+                                           lockdep_is_held(&tbl->lock));
+            n1 != NULL;
+            n1 = rcu_dereference_protected(n1->next,
+                       lockdep_is_held(&tbl->lock))) {
                if (dev == n1->dev && !memcmp(n1->primary_key, pkey, key_len)) {
                        neigh_hold(n1);
                        rc = n1;
@@ -491,10 +514,12 @@ struct neighbour *neigh_create(struct neigh_table *tbl, const void *pkey,
                }
        }
 
-       n->next = nht->hash_buckets[hash_val];
-       nht->hash_buckets[hash_val] = n;
        n->dead = 0;
        neigh_hold(n);
+       rcu_assign_pointer(n->next,
+                          rcu_dereference_protected(nht->hash_buckets[hash_val],
+                                                    lockdep_is_held(&tbl->lock)));
+       rcu_assign_pointer(nht->hash_buckets[hash_val], n);
        write_unlock_bh(&tbl->lock);
        NEIGH_PRINTK2("neigh %p is created.\n", n);
        rc = n;
@@ -651,6 +676,12 @@ static inline void neigh_parms_put(struct neigh_parms *parms)
                neigh_parms_destroy(parms);
 }
 
+static void neigh_destroy_rcu(struct rcu_head *head)
+{
+       struct neighbour *neigh = container_of(head, struct neighbour, rcu);
+
+       kmem_cache_free(neigh->tbl->kmem_cachep, neigh);
+}
 /*
  *     neighbour must already be out of the table;
  *
@@ -690,7 +721,7 @@ void neigh_destroy(struct neighbour *neigh)
        NEIGH_PRINTK2("neigh %p is destroyed.\n", neigh);
 
        atomic_dec(&neigh->tbl->entries);
-       kmem_cache_free(neigh->tbl->kmem_cachep, neigh);
+       call_rcu(&neigh->rcu, neigh_destroy_rcu);
 }
 EXPORT_SYMBOL(neigh_destroy);
 
@@ -731,7 +762,8 @@ static void neigh_connect(struct neighbour *neigh)
 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;
+       struct neighbour *n;
+       struct neighbour __rcu **np;
        unsigned int i;
        struct neigh_hash_table *nht;
 
@@ -756,7 +788,8 @@ static void neigh_periodic_work(struct work_struct *work)
        for (i = 0 ; i <= nht->hash_mask; i++) {
                np = &nht->hash_buckets[i];
 
-               while ((n = *np) != NULL) {
+               while ((n = rcu_dereference_protected(*np,
+                               lockdep_is_held(&tbl->lock))) != NULL) {
                        unsigned int state;
 
                        write_lock(&n->lock);
@@ -1213,8 +1246,8 @@ static void neigh_hh_init(struct neighbour *n, struct dst_entry *dst,
 }
 
 /* This function can be used in contexts, where only old dev_queue_xmit
-   worked, f.e. if you want to override normal output path (eql, shaper),
-   but resolution is not made yet.
+ * worked, f.e. if you want to override normal output path (eql, shaper),
+ * but resolution is not made yet.
  */
 
 int neigh_compat_output(struct sk_buff *skb)
@@ -2123,7 +2156,7 @@ static void neigh_update_notify(struct neighbour *neigh)
 static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
                            struct netlink_callback *cb)
 {
-       struct net * net = sock_net(skb->sk);
+       struct net *net = sock_net(skb->sk);
        struct neighbour *n;
        int rc, h, s_h = cb->args[1];
        int idx, s_idx = idx = cb->args[2];
@@ -2132,13 +2165,14 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
        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 = nht->hash_buckets[h], idx = 0; n; n = n->next) {
+               for (n = rcu_dereference_bh(nht->hash_buckets[h]), idx = 0;
+                    n != NULL;
+                    n = rcu_dereference_bh(n->next)) {
                        if (!net_eq(dev_net(n->dev), net))
                                continue;
                        if (idx < s_idx)
@@ -2150,13 +2184,12 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
                                rc = -1;
                                goto out;
                        }
-               next:
+next:
                        idx++;
                }
        }
        rc = skb->len;
 out:
-       read_unlock(&tbl->lock);
        rcu_read_unlock_bh();
        cb->args[1] = h;
        cb->args[2] = idx;
@@ -2195,11 +2228,13 @@ void neigh_for_each(struct neigh_table *tbl, void (*cb)(struct neighbour *, void
        rcu_read_lock_bh();
        nht = rcu_dereference_bh(tbl->nht);
 
-       read_lock(&tbl->lock);
+       read_lock(&tbl->lock); /* avoid resizes */
        for (chain = 0; chain <= nht->hash_mask; chain++) {
                struct neighbour *n;
 
-               for (n = nht->hash_buckets[chain]; n; n = n->next)
+               for (n = rcu_dereference_bh(nht->hash_buckets[chain]);
+                    n != NULL;
+                    n = rcu_dereference_bh(n->next))
                        cb(n, cookie);
        }
        read_unlock(&tbl->lock);
@@ -2217,16 +2252,20 @@ void __neigh_for_each_release(struct neigh_table *tbl,
        nht = rcu_dereference_protected(tbl->nht,
                                        lockdep_is_held(&tbl->lock));
        for (chain = 0; chain <= nht->hash_mask; chain++) {
-               struct neighbour *n, **np;
+               struct neighbour *n;
+               struct neighbour __rcu **np;
 
                np = &nht->hash_buckets[chain];
-               while ((n = *np) != NULL) {
+               while ((n = rcu_dereference_protected(*np,
+                                       lockdep_is_held(&tbl->lock))) != NULL) {
                        int release;
 
                        write_lock(&n->lock);
                        release = cb(n);
                        if (release) {
-                               *np = n->next;
+                               rcu_assign_pointer(*np,
+                                       rcu_dereference_protected(n->next,
+                                               lockdep_is_held(&tbl->lock)));
                                n->dead = 1;
                        } else
                                np = &n->next;
@@ -2250,7 +2289,7 @@ static struct neighbour *neigh_get_first(struct seq_file *seq)
 
        state->flags &= ~NEIGH_SEQ_IS_PNEIGH;
        for (bucket = 0; bucket <= nht->hash_mask; bucket++) {
-               n = nht->hash_buckets[bucket];
+               n = rcu_dereference_bh(nht->hash_buckets[bucket]);
 
                while (n) {
                        if (!net_eq(dev_net(n->dev), net))
@@ -2267,8 +2306,8 @@ static struct neighbour *neigh_get_first(struct seq_file *seq)
                                break;
                        if (n->nud_state & ~NUD_NOARP)
                                break;
-               next:
-                       n = n->next;
+next:
+                       n = rcu_dereference_bh(n->next);
                }
 
                if (n)
@@ -2292,7 +2331,7 @@ static struct neighbour *neigh_get_next(struct seq_file *seq,
                if (v)
                        return n;
        }
-       n = n->next;
+       n = rcu_dereference_bh(n->next);
 
        while (1) {
                while (n) {
@@ -2309,8 +2348,8 @@ static struct neighbour *neigh_get_next(struct seq_file *seq,
 
                        if (n->nud_state & ~NUD_NOARP)
                                break;
-               next:
-                       n = n->next;
+next:
+                       n = rcu_dereference_bh(n->next);
                }
 
                if (n)
@@ -2319,7 +2358,7 @@ static struct neighbour *neigh_get_next(struct seq_file *seq,
                if (++state->bucket > nht->hash_mask)
                        break;
 
-               n = nht->hash_buckets[state->bucket];
+               n = rcu_dereference_bh(nht->hash_buckets[state->bucket]);
        }
 
        if (n && pos)
@@ -2417,7 +2456,6 @@ 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;
@@ -2428,7 +2466,7 @@ void *neigh_seq_start(struct seq_file *seq, loff_t *pos, struct neigh_table *tbl
 
        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);
@@ -2461,13 +2499,8 @@ out:
 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(&tbl->lock);
        rcu_read_unlock_bh();
 }
 EXPORT_SYMBOL(neigh_seq_stop);