net: tipc: remove one synchronize_net() from tipc_nametbl_stop()

tipc_exit_net() is very slow and is abused by syzbot.

tipc_nametbl_stop() is called for each netns being dismantled.

Calling synchronize_net() right before freeing tn->nametbl
is a big hammer.

Replace this with kfree_rcu().

Note that RCU is not properly used here, otherwise
tn->nametbl should be cleared before the synchronize_net()
or kfree_rcu(), or even before the cleanup loop.

We might need to fix this at some point.

Also note tipc uses other synchronize_rcu() calls,
more work is needed to make tipc_exit_net() much faster.

List of remaining calls to synchronize_rcu()

  tipc_detach_loopback() (dev_remove_pack())
  tipc_bcast_stop()
  tipc_sk_rht_destroy()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241204210234.319484-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/tipc/name_table.h b/net/tipc/name_table.h
index 3bcd9ef8cee3..7ff6eeebaae6 100644
--- a/net/tipc/name_table.h
+++ b/net/tipc/name_table.h
@@ -90,6 +90,7 @@ struct publication {
 
 /**
  * struct name_table - table containing all existing port name publications
+ * @rcu: RCU callback head used for deferred freeing
  * @services: name sequence hash lists
  * @node_scope: all local publications with node scope
  *               - used by name_distr during re-init of name table
@@ -102,6 +103,7 @@ struct publication {
  * @snd_nxt: next sequence number to be used
  */
 struct name_table {
+	struct rcu_head rcu;
 	struct hlist_head services[TIPC_NAMETBL_SIZE];
 	struct list_head node_scope;
 	struct list_head cluster_scope;