netdev - Re: [PATCH rcu/dev 3/3] net: Use call_rcu_flush() for dst_destroy

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Date:   Thu, 17 Nov 2022 09:49:04 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
        David Ahern <dsahern@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
        Paolo Abeni <pabeni@...hat.com>, rcu@...r.kernel.org,
        rostedt@...dmis.org, paulmck@...nel.org, fweisbec@...il.com,
        jiejiang@...gle.com, Thomas Glexiner <tglx@...utronix.de>
Subject: Re: [PATCH rcu/dev 3/3] net: Use call_rcu_flush() for dst_destroy_rcu

On Thu, Nov 17, 2022 at 9:42 AM Joel Fernandes <joel@...lfernandes.org> wrote:
>

>
> Yes, I agree. Your comments here have not been useful (or respectful)
> so I am Ok with that.
>
>  - Joel

Well, I have discovered that some changes went in networking tree
without network maintainers being involved nor CCed.

What can I say ?

It seems I have no say, right ?


commit f32846476afbe1f296c41d036219178b3dfb6a9d
Author: Joel Fernandes (Google) <joel@...lfernandes.org>
Date:   Sun Oct 16 16:23:04 2022 +0000

    rxrpc: Use call_rcu_flush() instead of call_rcu()

    call_rcu() changes to save power may cause slowness. Use the
    call_rcu_flush() API instead which reverts to the old behavior.

    We find this via inspection that the RCU callback does a wakeup of a
    thread. This usually indicates that something is waiting on it. To be
    safe, let us use call_rcu_flush() here instead.

    Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

diff --git a/net/rxrpc/conn_object.c b/net/rxrpc/conn_object.c
index 22089e37e97f0628f780855f9e219e5c33d4afa1..fdcfb509cc4434b0781b76623532aff9c854ce60
100644
--- a/net/rxrpc/conn_object.c
+++ b/net/rxrpc/conn_object.c
@@ -253,7 +253,7 @@ void rxrpc_kill_connection(struct rxrpc_connection *conn)
         * must carry a ref on the connection to prevent us getting here whilst
         * it is queued or running.
         */
-       call_rcu(&conn->rcu, rxrpc_destroy_connection);
+       call_rcu_flush(&conn->rcu, rxrpc_destroy_connection);
 }

 /*