netfilter: nfnetlink_log: RCU conversion, part 2

- must use atomic_inc_not_zero() in instance_lookup_get()

- must use hlist_add_head_rcu() instead of hlist_add_head()

- must use hlist_del_rcu() instead of hlist_del()

- Introduce NFULNL_COPY_DISABLED to stop lockless reader from using an
instance, before we do final instance_put() on it.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 12 insertions, 6 deletions

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index 8ec23ec568e..fb86a51bb65 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -109,8 +109,8 @@ instance_lookup_get(u_int16_t group_num)
 
         rcu_read_lock_bh();
         inst = __instance_lookup(group_num);
-        if (inst)
-                instance_get(inst);
+        if (inst && !atomic_inc_not_zero(&inst->use))
+                inst = NULL;
         rcu_read_unlock_bh();
 
         return inst;
@@ -171,7 +171,7 @@ instance_create(u_int16_t group_num, int pid)
         inst->copy_mode         = NFULNL_COPY_PACKET;
         inst->copy_range        = NFULNL_COPY_RANGE_MAX;
 
-        hlist_add_head(&inst->hlist,
+        hlist_add_head_rcu(&inst->hlist,
                        &instance_table[instance_hashfn(group_num)]);
 
         spin_unlock_bh(&instances_lock);
@@ -185,18 +185,23 @@ out_unlock:
 
 static void __nfulnl_flush(struct nfulnl_instance *inst);
 
+/* called with BH disabled */
 static void
 __instance_destroy(struct nfulnl_instance *inst)
 {
         /* first pull it out of the global list */
-        hlist_del(&inst->hlist);
+        hlist_del_rcu(&inst->hlist);
 
         /* then flush all pending packets from skb */
 
-        spin_lock_bh(&inst->lock);
+        spin_lock(&inst->lock);
+
+        /* lockless readers wont be able to use us */
+        inst->copy_mode = NFULNL_COPY_DISABLED;
+
         if (inst->skb)
                 __nfulnl_flush(inst);
-        spin_unlock_bh(&inst->lock);
+        spin_unlock(&inst->lock);
 
         /* and finally put the refcount */
         instance_put(inst);
@@ -624,6 +629,7 @@ nfulnl_log_packet(u_int8_t pf,
                 size += nla_total_size(data_len);
                 break;
 
+        case NFULNL_COPY_DISABLED:
         default:
                 goto unlock_and_release;
         }