[PATCH 6.6 041/322] rxrpc_find_service_conn_rcu: fix the usage of read_seqbegin_or_lock()

Greg Kroah-Hartman
2024-02-03T04:12:04Z

From: Oleg Nesterov <oleg@redhat.com>

[ Upstream commit bad1a11c0f061aa073bab785389fe04f19ba02e1 ]

rxrpc_find_service_conn_rcu() should make the "seq" counter odd on the
second pass, otherwise read_seqbegin_or_lock() never takes the lock.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/20231117164846.GA10410@redhat.com/
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/rxrpc/conn_service.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/conn_service.c b/net/rxrpc/conn_service.c
index 89ac05a711a4..39c908a3ca6e 100644
--- a/net/rxrpc/conn_service.c
+++ b/net/rxrpc/conn_service.c
@@ -25,7 +25,7 @@ struct rxrpc_connection *rxrpc_find_service_conn_rcu(struct rxrpc_peer *peer,
struct rxrpc_conn_proto k;
struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
struct rb_node *p;
- unsigned int seq = 0;
+ unsigned int seq = 1;

k.epoch = sp->hdr.epoch;
k.cid = sp->hdr.cid & RXRPC_CIDMASK;
@@ -35,6 +35,7 @@ struct rxrpc_connection *rxrpc_find_service_conn_rcu(struct rxrpc_peer *peer,
* under just the RCU read lock, so we have to check for
* changes.
*/
+ seq++; /* 2 on the 1st/lockless path, otherwise odd */
read_seqbegin_or_lock(&peer->service_conn_lock, &seq);

p = rcu_dereference_raw(peer->service_conns.rb_node);
--
2.43.0