[PATCH 4.20 44/76] tipc: fix race condition causing hung sendto

Greg Kroah-Hartman
2019-03-08T13:06:33Z

From: Tung Nguyen <tung.q.nguyen@dektech.com.au>

[ Upstream commit bfd07f3dd4f111b884d7922b37eb239280f83d8c ]

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.maloy@ericsson.com>
Signed-off-by: Tung Nguyen <tung.q.nguyen@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/tipc/socket.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -376,11 +376,13 @@ static int tipc_sk_sock_err(struct socke

#define tipc_wait_for_cond(sock_, timeo_, condition_) \
({ \
+ DEFINE_WAIT_FUNC(wait_, woken_wake_function); \
struct sock *sk_; \
int rc_; \
\
while ((rc_ = !(condition_))) { \
- DEFINE_WAIT_FUNC(wait_, woken_wake_function); \
+ /* coupled with smp_wmb() in tipc_sk_proto_rcv() */ \
+ smp_rmb(); \
sk_ = (sock_)->sk; \
rc_ = tipc_sk_sock_err((sock_), timeo_); \
if (rc_) \
@@ -1968,6 +1970,8 @@ static void tipc_sk_proto_rcv(struct soc
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;