> -----Original Message----- > From: Xue, Ying [mailto:[email protected]] > Sent: Tuesday, 14 June, 2016 05:46 > To: Jon Maloy; [email protected]; Parthasarathy > Bhuvaragan; > Richard Alpe > Cc: [email protected]; [email protected] > Subject: RE: [PATCH net v3 1/1] tipc: fix socket timer deadlock > > I concern whether it's really safe for us by testing socket owner instead of > sk_lock.slock. > We have identified the deadlock reason is because tipc_sk_respond() is called > under socket lock. > > Just for the case of responding to CONN_MANAGER messages, testing socket > owner is safe. But the solution seems unsafe when TIPC_ERR_OVERLOAD > message is sent. > > While TIPC_ERR_OVERLOAD is sent out under BH context, socket's owner is set.
Where? There are two locations where tipc_sk_respond() may be sent under BH, in tipc_sk_enqueue() and filter_rcv(), but it is either-or: either we are under BH, and socket is not owned, or it is owned, and we are not under BH. I don't see at all what you are referring to. Regards ///jon > So the message will be sent out under BH through tipc_node_xmit_skb() instead > of insert it into sk->sk_write_queue. > > Regards, > Ying > > -----Original Message----- > From: Jon Maloy [mailto:[email protected]] > Sent: Tuesday, June 14, 2016 1:51 AM > To: [email protected]; > [email protected]; Xue, Ying; [email protected]; > [email protected] > Cc: [email protected]; [email protected] > Subject: [PATCH net v3 1/1] tipc: fix socket timer deadlock > > We sometimes observe a 'deadly embrace' type deadlock occurring between > mutually connected sockets on the same node. This happens when the one-hour > peer supervision timers happen to expire simultaneously in both sockets. > > The scenario is as follows: > > CPU 1: CPU 2: > -------- -------- > tipc_sk_timeout(sk1) tipc_sk_timeout(sk2) > lock(sk1.slock) lock(sk2.slock) > msg_create(probe) msg_create(probe) > unlock(sk1.slock) unlock(sk2.slock) > tipc_node_xmit_skb() tipc_node_xmit_skb() > tipc_node_xmit() tipc_node_xmit() > tipc_sk_rcv(sk2) tipc_sk_rcv(sk1) > lock(sk2.slock) lock((sk1.slock) > filter_rcv() filter_rcv() > tipc_sk_proto_rcv() tipc_sk_proto_rcv() > msg_create(probe_rsp) msg_create(probe_rsp) > tipc_sk_respond() tipc_sk_respond() > tipc_node_xmit_skb() tipc_node_xmit_skb() > tipc_node_xmit() tipc_node_xmit() > tipc_sk_rcv(sk1) tipc_sk_rcv(sk2) > lock((sk1.slock) lock((sk2.slock) > ===> DEADLOCK ===> DEADLOCK > > Further analysis reveals that there are at least three different locations in > the > socket code where tipc_sk_respond() is called within the context of the socket > lock, with ensuing risk of similar deadlocks. > > We solve this by ensuring that messages created by tipc_sk_respond() only are > sent directly if sk_lock.owned mutex is held. Otherwise they are queued up in > the socket write queue and sent after the socket lock has been released. > > v2: - Testing on mutex sk_lock.owned instead of sk_lock.slock in > tipc_sk_respond(). This is safer, since sk_lock.slock may > occasionally and briefly be held (by concurrent user contexts) > even if we are in user context. > v3: - By lowering the socket timeout to 36 ms instead of 3,600,000 and > setting up 1000 connections I could easily reproduce the deadlock > and verify that my solution works. > - When killing one of the processes I sometimes got a kernel crash > in the loop emptying the socket write queue. Realizing that there > may be concurrent processes emptying the write queue, I had to add > a test that the dequeuing actually returned a buffer. This solved > the problem. > - I tried Ying's suggestion with unconditionally adding all > CONN_MANAGER messages to the backlog queue, and it didn't work. > This is because we will often add the message to the backlog when > the socket is *not* owned, so there will be nothing triggering > execution of backlog_rcv() within acceptable time. Apart from > that, my solution solves the problem at all three locations where > this deadlock may happen, as already stated above. > > Reported-by: GUNA <[email protected]> > Signed-off-by: Jon Maloy <[email protected]> > --- > net/tipc/socket.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/net/tipc/socket.c b/net/tipc/socket.c index 88bfcd7..e8ed3a8 > 100644 > --- a/net/tipc/socket.c > +++ b/net/tipc/socket.c > @@ -278,7 +278,11 @@ static void tipc_sk_respond(struct sock *sk, struct > sk_buff *skb, int err) > > dnode = msg_destnode(buf_msg(skb)); > selector = msg_origport(buf_msg(skb)); > - tipc_node_xmit_skb(sock_net(sk), skb, dnode, selector); > + > + if (sock_owned_by_user(sk)) > + tipc_node_xmit_skb(sock_net(sk), skb, dnode, selector); > + else > + skb_queue_tail(&sk->sk_write_queue, skb); > } > > /** > @@ -1830,6 +1834,14 @@ void tipc_sk_rcv(struct net *net, struct sk_buff_head > *inputq) > tipc_sk_enqueue(inputq, sk, dport); > spin_unlock_bh(&sk->sk_lock.slock); > } > + /* Send pending response/rejected messages, if any */ > + while (!skb_queue_empty(&sk->sk_write_queue)) { > + skb = skb_dequeue(&sk->sk_write_queue); > + if (!skb) > + break; > + dnode = msg_destnode(buf_msg(skb)); > + tipc_node_xmit_skb(net, skb, dnode, dport); > + } > sock_put(sk); > continue; > } > -- > 1.9.1 ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? 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