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lnd: eliminate deadlock bug between htlcSwitch and htlcManager

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This commit fixes a concurrency bug between the server’s htlc switch,
and an instance of a peer’s active htlc manager goroutine.

The deadlock condition was triggered when the htlc manager’s downstream
`htlcPacket` channel was full, causing the htlcSwitch’s main loop to
block on a send while the htlcManager was attempting to send a packet
to the switch for forwarding. This scenario created a circular
dependency resting in a deadlock.

The fix for this bug is relatively straight forward, if the destination
interface is found when handling an outgoing payment, then a new
goroutine is spawned to complete the request.
This commit is contained in:
Olaoluwa Osuntokun 2016-07-24 17:03:40 -07:00
parent 06f32cd5bc
commit 82ea6ebf78
No known key found for this signature in database
GPG Key ID: 9CC5B105D03521A2
1 changed files with 36 additions and 18 deletions
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54
htlcswitch.go
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@ -131,7 +131,10 @@ func (h *htlcSwitch) SendHTLC(htlcPkt *htlcPacket) error {
// htlcForwarder is responsible for optimally forwarding (and possibly
// fragmenting) incoming/outgoing HTLC's amongst all active interfaces and
// their links.
// their links. The duties of the forwarder are similar to that of a network
// switch, in that it facilitates multi-hop payments by acting as a central
// messaging bus. Each active channel is modeled as networked device with
// meta-data such as the available payment bandwidth, and total link capacity.
func (h *htlcSwitch) htlcForwarder() {
// TODO(roasbeef): track pending payments here instead of within each peer?
// Examine settles/timeouts from htl cplex. Add src to htlcPacket, key by
@ -145,9 +148,10 @@ out:
for {
select {
case htlcPkt := <-h.outgoingPayments:
chanInterface, ok := h.interfaces[htlcPkt.dest]
dest := htlcPkt.dest
chanInterface, ok := h.interfaces[dest]
if !ok {
err := fmt.Errorf("unable to locate link %x", htlcPkt.dest[:])
err := fmt.Errorf("Unable to locate link %x", dest)
hswcLog.Errorf(err.Error())
htlcPkt.err <- err
continue
@ -156,28 +160,39 @@ out:
wireMsg := htlcPkt.msg.(*lnwire.HTLCAddRequest)
amt := btcutil.Amount(wireMsg.Amount)
// Handle this send request in a distinct goroutine in
// order to avoid a possible deadlock between the htlc
// switch and channel's htlc manager.
var sent bool
for _, link := range chanInterface {
// TODO(roasbeef): implement HTLC fragmentation
if link.availableBandwidth >= amt {
hswcLog.Tracef("Sending %v to %x", amt,
htlcPkt.dest[:])
// TODO(roasbeef): peer downstream should set chanPoint
wireMsg.ChannelPoint = link.chanPoint
link.linkChan <- htlcPkt
// TODO(roasbeef): update link info on
// timeout/settle
link.availableBandwidth -= amt
break
// * avoid full channel depletion at higher
// level (here) instead of within state
// machine?
if link.availableBandwidth < amt {
continue
}
hswcLog.Tracef("Sending %v to %x", amt, dest)
// TODO(roasbeef): peer downstream should set chanPoint
wireMsg.ChannelPoint = link.chanPoint
go func() {
link.linkChan <- htlcPkt
}()
// TODO(roasbeef): update link info on
// timeout/settle
link.availableBandwidth -= amt
sent = true
}
if wireMsg.ChannelPoint == nil {
hswcLog.Errorf("unable to send payment, " +
"insufficient capacity")
htlcPkt.err <- fmt.Errorf("insufficient capacity")
if sent {
continue
}
hswcLog.Errorf("Unable to send payment, insufficient capacity")
htlcPkt.err <- fmt.Errorf("Insufficient capacity")
case pkt := <-h.htlcPlex:
numUpdates += 1
// TODO(roasbeef): properly account with cleared vs settled
@ -187,6 +202,9 @@ out:
case *lnwire.HTLCSettleRequest:
satSent += pkt.amt
}
// TODO(roasbeef): parse dest/src, forward on outgoing
// link to complete multi-hop payments.
case <-logTicker.C:
if numUpdates == 0 {
continue