net: napi_hash_del() returns a boolean status

napi_hash_del() will soon be used from both drivers (if they want)
or core networking stack.

Callers are responsibles to ensure an RCU grace period is respected
before freeing napi structure : napi_hash_del() can signal if
this RCU grace period is needed or not.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -474,9 +474,10 @@ void napi_hash_add(struct napi_struct *napi);
  *	@napi: napi context
  *
  * Warning: caller must observe rcu grace period
- * before freeing memory containing @napi
+ * before freeing memory containing @napi, if
+ * this function returns true.
  */
-void napi_hash_del(struct napi_struct *napi);
+bool napi_hash_del(struct napi_struct *napi);
 
 /**
  *	napi_disable - prevent NAPI from scheduling

net/core/dev.c

@@ -4760,14 +4760,18 @@ EXPORT_SYMBOL_GPL(napi_hash_add);
 /* Warning : caller is responsible to make sure rcu grace period
  * is respected before freeing memory containing @napi
  */
-void napi_hash_del(struct napi_struct *napi)
+bool napi_hash_del(struct napi_struct *napi)
 {
+	bool rcu_sync_needed = false;
+
 	spin_lock(&napi_hash_lock);
 
-	if (test_and_clear_bit(NAPI_STATE_HASHED, &napi->state))
+	if (test_and_clear_bit(NAPI_STATE_HASHED, &napi->state)) {
+		rcu_sync_needed = true;
 		hlist_del_rcu(&napi->napi_hash_node);
-
+	}
 	spin_unlock(&napi_hash_lock);
+	return rcu_sync_needed;
 }
 EXPORT_SYMBOL_GPL(napi_hash_del);