netdev - Re: [net v3 1/1] tipc: fix race condition causing hung sendto

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Date:   Tue, 26 Feb 2019 14:52:15 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     tung.q.nguyen@...tech.com.au
Cc:     netdev@...r.kernel.org, tipc-discussion@...ts.sourceforge.net
Subject: Re: [net v3 1/1] tipc: fix race condition causing hung sendto

From: Tung Nguyen <tung.q.nguyen@...tech.com.au>
Date: Mon, 25 Feb 2019 10:57:20 +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@...csson.com>
> Signed-off-by: Tung Nguyen <tung.q.nguyen@...tech.com.au>

Applied and queued up for -stable.