netdev - Re: [PATCH net-next] net: bonding: correctly annotate RCU in bond_should_notify

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Message-ID: <2730155.1721581793@famine>
Date: Sun, 21 Jul 2024 10:09:53 -0700
From: Jay Vosburgh <jv@...sburgh.net>
To: Johannes Berg <johannes@...solutions.net>
cc: netdev@...r.kernel.org, Andy Gospodarek <andy@...yhouse.net>,
    Johannes Berg <johannes.berg@...el.com>,
    Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next] net: bonding: correctly annotate RCU in
 bond_should_notify_peers()

Johannes Berg <johannes@...solutions.net> wrote:

>From: Johannes Berg <johannes.berg@...el.com>
>
>RCU use in bond_should_notify_peers() looks wrong, since it does
>rcu_dereference(), leaves the critical section, and uses the
>pointer after that.
>
>Luckily, it's called either inside a nested RCU critical section
>or with the RTNL held.
>
>Annotate it with rcu_dereference_rtnl() instead, and remove the
>inner RCU critical section.
>
>Fixes: 4cb4f97b7e36 ("bonding: rebuild the lock use for bond_mii_monitor()")
>Reviewed-by: Jiri Pirko <jiri@...dia.com>
>Signed-off-by: Johannes Berg <johannes.berg@...el.com>

Acked-by: Jay Vosburgh <jv@...sburgh.net>

>---
> drivers/net/bonding/bond_main.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index d19aabf5d4fb..2ed0da068490 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -1121,13 +1121,10 @@ static struct slave *bond_find_best_slave(struct bonding *bond)
> 	return bestslave;
> }
> 
>+/* must be called in RCU critical section or with RTNL held */
> static bool bond_should_notify_peers(struct bonding *bond)
> {
>-	struct slave *slave;
>-
>-	rcu_read_lock();
>-	slave = rcu_dereference(bond->curr_active_slave);
>-	rcu_read_unlock();
>+	struct slave *slave = rcu_dereference_rtnl(bond->curr_active_slave);
> 
> 	if (!slave || !bond->send_peer_notif ||
> 	    bond->send_peer_notif %
>-- 
>2.45.2
>