linux-kernel - RE: [RFC PATCH] net/tipc: reduce tipc_node lock holding time in tipc

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Message-Id: <20231123062205.2038335-1-xu.xin16@zte.com.cn>
Date:   Thu, 23 Nov 2023 06:22:05 +0000
From:   xu <xu.xin.sc@...il.com>
To:     tung.q.nguyen@...tech.com.au
Cc:     davem@...emloft.net, jmaloy@...hat.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        tipc-discussion@...ts.sourceforge.net, xu.xin.sc@...il.com,
        xu.xin16@....com.cn, ying.xue@...driver.com, yang.yang29@....com.cn
Subject: RE: [RFC PATCH] net/tipc: reduce tipc_node lock holding time in tipc_rcv

>>diff --git a/net/tipc/node.c b/net/tipc/node.c index 3105abe97bb9..2a036b8a7da3 100644
>>--- a/net/tipc/node.c
>>+++ b/net/tipc/node.c
>>@@ -2154,14 +2154,15 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
>> 	/* Receive packet directly if conditions permit */
>> 	tipc_node_read_lock(n);
>> 	if (likely((n->state == SELF_UP_PEER_UP) && (usr != TUNNEL_PROTOCOL))) {
>>+		tipc_node_read_unlock(n);
>> 		spin_lock_bh(&le->lock);
>> 		if (le->link) {
>> 			rc = tipc_link_rcv(le->link, skb, &xmitq);
>> 			skb = NULL;
>> 		}
>> 		spin_unlock_bh(&le->lock);
>>-	}
>>-	tipc_node_read_unlock(n);
>>+	} else
>>+		tipc_node_read_unlock(n);
>>
>> 	/* Check/update node state before receiving */
>> 	if (unlikely(skb)) {
>>@@ -2169,12 +2170,13 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
>> 			goto out_node_put;
>> 		tipc_node_write_lock(n);
>> 		if (tipc_node_check_state(n, skb, bearer_id, &xmitq)) {
>>+			tipc_node_write_unlock(n);
>> 			if (le->link) {
>> 				rc = tipc_link_rcv(le->link, skb, &xmitq);
>> 				skb = NULL;
>> 			}
>>-		}
>>-		tipc_node_write_unlock(n);
>>+		} else
>>+			tipc_node_write_unlock(n);
>> 	}
>>
>> 	if (unlikely(rc & TIPC_LINK_UP_EVT))
>>--
>>2.15.2
>>
>>
>This patch is wrong. le->link and link status must be protected by node lock. See what happens if tipc_node_timeout() is called, and the link goes down:
>tipc_node_timeout()
>   tipc_node_link_down()
>   {
>      struct tipc_link *l = le->link;
>      ...
>      if (delete) {
>         kfree(l);
>         le->link = NULL;
>      }
>      ...
>   }

Happy to see your reply. But Why? 'delete' is false from tipc_node_timeout(). Refer to:
https://elixir.bootlin.com/linux/v6.7-rc2/source/net/tipc/node.c#L844