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

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Message-ID: <DB9PR05MB9078FE84F8244C627FDCFA2888B8A@DB9PR05MB9078.eurprd05.prod.outlook.com>
Date:   Fri, 24 Nov 2023 08:28:56 +0000
From:   Tung Quang Nguyen <tung.q.nguyen@...tech.com.au>
To:     xu <xu.xin.sc@...il.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "jmaloy@...hat.com" <jmaloy@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        "xu.xin16@....com.cn" <xu.xin16@....com.cn>,
        "yang.yang29@....com.cn" <yang.yang29@....com.cn>,
        "ying.xue@...driver.com" <ying.xue@...driver.com>,
        "zhang.yunkai@....com.cn" <zhang.yunkai@....com.cn>
Subject: RE: [RFC PATCH] net/tipc: reduce tipc_node lock holding time in
 tipc_rcv

>Could we please solve the problem mentioned above by adding spinlock(&le->lock)?
>

No, you cannot do that. As I said before, the link status (including l->state) needs to be protected by node lock.
What I showed you were just 2 use cases (link reset/delete). There are more use cases (netlink, transmit path etc) that need proper locks.

>For example:
>
>(BTW, I have tested it, with this change, enabling RPS based on tipc port can improve 25% of general throughput)
>
>diff --git a/net/tipc/node.c b/net/tipc/node.c index 3105abe97bb9..470c272d798e 100644
>--- a/net/tipc/node.c
>+++ b/net/tipc/node.c
>@@ -1079,12 +1079,16 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id, bool delete)
>                __tipc_node_link_down(n, &bearer_id, &xmitq, &maddr);
>        } else {
>                /* Defuse pending tipc_node_link_up() */
>+               spin_lock_bh(&le->lock);
>                tipc_link_reset(l);
>+               spin_unlock_bh(&le->lock);
>                tipc_link_fsm_evt(l, LINK_RESET_EVT);
>        }
>        if (delete) {
>+               spin_lock_bh(&le->lock);
>                kfree(l);
>                le->link = NULL;
>+               spin_unlock_bh(&le->lock);
>                n->link_cnt--;
>        }
>        trace_tipc_node_link_down(n, true, "node link down or deleted!"); @@ -2154,14 +2158,15 @@ 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 +2174,13 @@ 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))