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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>
bfd07f3dd4