When sending multicast messages via blocking socket,
if sending link is congested (tsk->cong_link_cnt is set to 1),
the sending thread will be put into sleeping state. However,
tipc_sk_filter_rcv() is called under socket spin lock but
tipc_wait_for_cond() is not. So, there is no guarantee that
the setting of tsk->cong_link_cnt to 0 in tipc_sk_proto_rcv() in
CPU-1 will be perceived by CPU-0. If that is the case, the sending
thread in CPU-0 after being waken up, will continue to see
tsk->cong_link_cnt as 1 and put the sending thread into sleeping
state again. The sending thread will sleep forever.
CPU-0 | CPU-1
tipc_wait_for_cond() |
{ |
// condition_ = !tsk->cong_link_cnt |
while ((rc_ = !(condition_))) { |
... |
release_sock(sk_); |
wait_woken(); |
| if (!sock_owned_by_user(sk))
| tipc_sk_filter_rcv()
| {
| ...
| tipc_sk_proto_rcv()
| {
| ...
| tsk->cong_link_cnt--;
| ...
| sk->sk_write_space(sk);
| ...
| }
| ...
| }
sched_annotate_sleep(); |
lock_sock(sk_); |
remove_wait_queue(); |
} |
} |
This commit fixes it by adding memory barrier to tipc_sk_proto_rcv()
and tipc_wait_for_cond().
Acked-by: Jon Maloy <jon.ma...@ericsson.com>
Signed-off-by: Tung Nguyen <tung.q.ngu...@dektech.com.au>
---
net/tipc/socket.c | 4 ++++
1 file changed, 4 insertions(+)
mode change 100644 => 100755 net/tipc/socket.c
diff --git a/net/tipc/socket.c b/net/tipc/socket.c
old mode 100644
new mode 100755
index 1217c90a363b..d8f054d45941
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -383,6 +383,8 @@ static int tipc_sk_sock_err(struct socket *sock, long
*timeout)
int rc_; \
\
while ((rc_ = !(condition_))) { \
+ /* coupled with smp_wmb() in tipc_sk_proto_rcv() */ \
+ smp_rmb(); \
DEFINE_WAIT_FUNC(wait_, woken_wake_function); \
sk_ = (sock_)->sk; \
rc_ = tipc_sk_sock_err((sock_), timeo_); \
@@ -1982,6 +1984,8 @@ static void tipc_sk_proto_rcv(struct sock *sk,
return;
case SOCK_WAKEUP:
tipc_dest_del(&tsk->cong_links, msg_orignode(hdr), 0);
+ /* coupled with smp_rmb() in tipc_wait_for_cond() */
+ smp_wmb();
tsk->cong_link_cnt--;
wakeup = true;
break;
--
2.17.1
