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

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Message-ID: <20240719094119.35c62455087d.I68eb9c0f02545b364b79a59f2110f2cf5682a8e2@changeid>
Date: Fri, 19 Jul 2024 09:41:18 -0700
From: Johannes Berg <johannes@...solutions.net>
To: netdev@...r.kernel.org
Cc: Jay Vosburgh <j.vosburgh@...il.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Johannes Berg <johannes.berg@...el.com>,
	Jiri Pirko <jiri@...dia.com>
Subject: [PATCH net-next] net: bonding: correctly annotate RCU in bond_should_notify_peers()

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>
---
 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