[PATCH net-next 07/14] mptcp: annotate data-races around pernet sysctls

[Jiayuan Chen <jiayuan.chen@linux.dev>]

enabled, add_addr_timeout, checksum_enabled, allow_join_initial_addr_port,
stale_loss_cnt, close_timeout, pm_type and syn_retrans_before_tcp_fallback
are read by their ctrl.c helpers without any lock while the sysctl
handlers update them with WRITE_ONCE(), and the path_manager handler
stores pm_type with a plain write. Add READ_ONCE() to the readers and
WRITE_ONCE() to that handler.

KCSAN reports it when net.mptcp.enabled is changed while MPTCP sockets
are being created:

  BUG: KCSAN: data-race in mptcp_is_enabled / proc_dou8vec_minmax

  write (marked) to 0xffff8d724248abc9 of 1 bytes by task 733 on cpu 3:
   proc_dou8vec_minmax+0x1ab/0x1f0
   proc_sys_call_handler+0x282/0x3a0
   proc_sys_write+0x13/0x20
   ...

  read to 0xffff8d724248abc9 of 1 bytes by task 735 on cpu 1:
   mptcp_is_enabled+0x33/0x50
   mptcp_init_sock+0x35/0x300
   inet_create+0x4a6/0x8e0
   ...

  value changed: 0x00 -> 0x01

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 net/mptcp/ctrl.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 63c5747f0f63c..164f79b9deb0e 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -50,39 +50,39 @@ static struct mptcp_pernet *mptcp_get_pernet(const struct net *net)
 
 int mptcp_is_enabled(const struct net *net)
 {
-	return mptcp_get_pernet(net)->mptcp_enabled;
+	return READ_ONCE(mptcp_get_pernet(net)->mptcp_enabled);
 }
 
 unsigned int mptcp_get_add_addr_timeout(const struct net *net)
 {
-	return mptcp_get_pernet(net)->add_addr_timeout;
+	return READ_ONCE(mptcp_get_pernet(net)->add_addr_timeout);
 }
 
 int mptcp_is_checksum_enabled(const struct net *net)
 {
-	return mptcp_get_pernet(net)->checksum_enabled;
+	return READ_ONCE(mptcp_get_pernet(net)->checksum_enabled);
 }
 
 int mptcp_allow_join_id0(const struct net *net)
 {
-	return mptcp_get_pernet(net)->allow_join_initial_addr_port;
+	return READ_ONCE(mptcp_get_pernet(net)->allow_join_initial_addr_port);
 }
 
 unsigned int mptcp_stale_loss_cnt(const struct net *net)
 {
-	return mptcp_get_pernet(net)->stale_loss_cnt;
+	return READ_ONCE(mptcp_get_pernet(net)->stale_loss_cnt);
 }
 
 unsigned int mptcp_close_timeout(const struct sock *sk)
 {
 	if (sock_flag(sk, SOCK_DEAD))
 		return TCP_TIMEWAIT_LEN;
-	return mptcp_get_pernet(sock_net(sk))->close_timeout;
+	return READ_ONCE(mptcp_get_pernet(sock_net(sk))->close_timeout);
 }
 
 int mptcp_get_pm_type(const struct net *net)
 {
-	return mptcp_get_pernet(net)->pm_type;
+	return READ_ONCE(mptcp_get_pernet(net)->pm_type);
 }
 
 const char *mptcp_get_path_manager(const struct net *net)
@@ -230,7 +230,7 @@ static int proc_path_manager(const struct ctl_table *ctl, int write,
 				pm_type = MPTCP_PM_TYPE_KERNEL;
 			else if (strncmp(pm_name, "userspace", MPTCP_PM_NAME_MAX) == 0)
 				pm_type = MPTCP_PM_TYPE_USERSPACE;
-			pernet->pm_type = pm_type;
+			WRITE_ONCE(pernet->pm_type, pm_type);
 		}
 	}
 
@@ -551,7 +551,7 @@ void mptcp_active_detect_blackhole(struct sock *ssk, bool expired)
 
 	net = sock_net(ssk);
 	timeouts = inet_csk(ssk)->icsk_retransmits;
-	to_max = mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback;
+	to_max = READ_ONCE(mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback);
 
 	if (timeouts == to_max || (timeouts < to_max && expired)) {
 		subflow->mpc_drop = 1;
-- 
2.43.0