From: Eric Dumazet <eduma...@google.com>
In my first attempt to fix the lockdep splat, I forgot we could
enter inet_csk_route_req() with a freshly allocated request socket,
for which refcount has not yet been elevated, due to complex
SLAB_TYPESAFE_BY_RCU rules.
We either are in rcu_read_lock() section _or_ we own a refcount on the
request.
Correct RCU verb to use here is rcu_dereference_check(), although it is
not possible to prove we actually own a reference on a shared
refcount :/
[ 49.844590] lockdep_rcu_suspicious+0xea/0xf3
[ 49.846487] inet_csk_route_req+0x53/0x14d
[ 49.848334] tcp_v4_route_req+0xe/0x10
[ 49.850174] tcp_conn_request+0x31c/0x6a0
[ 49.851992] ? __lock_acquire+0x614/0x822
[ 49.854015] tcp_v4_conn_request+0x5a/0x79
[ 49.855957] ? tcp_v4_conn_request+0x5a/0x79
[ 49.858052] tcp_rcv_state_process+0x98/0xdcc
[ 49.859990] ? sk_filter_trim_cap+0x2f6/0x307
[ 49.862085] tcp_v4_do_rcv+0xfc/0x145
[ 49.864055] ? tcp_v4_do_rcv+0xfc/0x145
[ 49.866173] tcp_v4_rcv+0x5ab/0xaf9
[ 49.868029] ip_local_deliver_finish+0x1af/0x2e7
[ 49.870064] ip_local_deliver+0x1b2/0x1c5
[ 49.871775] ? inet_del_offload+0x45/0x45
[ 49.873916] ip_rcv_finish+0x3f7/0x471
[ 49.875476] ip_rcv+0x3f1/0x42f
[ 49.876991] ? ip_local_deliver_finish+0x2e7/0x2e7
[ 49.878791] __netif_receive_skb_core+0x6d3/0x950
[ 49.880701] ? process_backlog+0x7e/0x216
[ 49.882589] __netif_receive_skb+0x1d/0x5e
[ 49.884122] process_backlog+0x10c/0x216
[ 49.885812] net_rx_action+0x147/0x3df
Fixes: a6ca7abe53633 ("tcp/dccp: fix lockdep splat in inet_csk_route_req()")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: kernel test robot <fengguang...@intel.com>
Reported-by: Maciej Żenczykowski <m...@google.com>
---
net/ipv4/inet_connection_sock.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index
18cd2eae758ff1a9d8a736e143417c7007b99067..08381782830b50cac621c531a4e7e1cf8dc6577f
100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -543,8 +543,8 @@ struct dst_entry *inet_csk_route_req(const struct sock *sk,
struct ip_options_rcu *opt;
struct rtable *rt;
- opt = rcu_dereference_protected(ireq->ireq_opt,
- refcount_read(&req->rsk_refcnt) > 0);
+ opt = rcu_dereference_check(ireq->ireq_opt,
+ refcount_read(&req->rsk_refcnt) > 0);
flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
sk->sk_protocol, inet_sk_flowi_flags(sk),
