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

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Message-ID: <DB9PR05MB9078636E4D78B9F4442898B088B9A@DB9PR05MB9078.eurprd05.prod.outlook.com>
Date:   Thu, 23 Nov 2023 04:12:54 +0000
From:   Tung Quang Nguyen <tung.q.nguyen@...tech.com.au>
To:     "xu.xin.sc@...il.com" <xu.xin.sc@...il.com>,
        "jmaloy@...hat.com" <jmaloy@...hat.com>,
        "ying.xue@...driver.com" <ying.xue@...driver.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xu.xin16@....com.cn" <xu.xin16@....com.cn>
Subject: RE: [RFC PATCH] net/tipc: reduce tipc_node lock holding time in
 tipc_rcv

> net/tipc/node.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
>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;
      }
      ...
   }