netdev - [PATCH RFC bpf-next 2/4] dev: add rcu_read_lock_bh_held() as a valid check when getting a RCU dev ref

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Message-ID: <161917591778.102337.1084869564077259501.stgit@toke.dk>
Date:   Fri, 23 Apr 2021 13:05:17 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, Martin KaFai Lau <kafai@...com>,
        Hangbin Liu <liuhangbin@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH RFC bpf-next 2/4] dev: add rcu_read_lock_bh_held() as a valid
 check when getting a RCU dev ref

From: Toke Høiland-Jørgensen <toke@...hat.com>

Some of the XDP helpers (in particular, xdp_do_redirect()) will get a
struct net_device reference using dev_get_by_index_rcu(). These are called
from a NAPI poll context, which means the RCU reference liveness is ensured
by local_bh_disable(). Add rcu_read_lock_bh_held() as a condition to the
RCU list traversal in dev_get_by_index_rcu() so lockdep understands that
the dereferences are safe from *both* an rcu_read_lock() *and* with
local_bh_disable().

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 net/core/dev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index b4c67a5be606..a7b8e3289f7c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1002,7 +1002,7 @@ struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex)
 	struct net_device *dev;
 	struct hlist_head *head = dev_index_hash(net, ifindex);
 
-	hlist_for_each_entry_rcu(dev, head, index_hlist)
+	hlist_for_each_entry_rcu(dev, head, index_hlist, rcu_read_lock_bh_held())
 		if (dev->ifindex == ifindex)
 			return dev;