Re: [tipc-discussion][net 1/1] tipc: fix race condition causing hung sendto

[David Miller <davem@davemloft.net>]

From: Tung Nguyen <tung.q.nguyen@dektech.com.au>
Date: Tue, 19 Feb 2019 14:03:10 +0700

> 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.
 ...
> 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>

You really need to build test this stuff properly:

net/tipc/socket.c: In function ‘__tipc_shutdown’:
./include/linux/wait.h:1119:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
  struct wait_queue_entry name = {     \
  ^~~~~~

You can't put the smp_rmb(); before the DEFINE_WAIT_FUNC() in that
basic block.