akovalenko/lnd.xprv
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

htlcswitch: fix alignment of the packetQueue's fields for 32-bit systems (#507)

Browse Source 
In this commit, we fix an existing issue that would cause lnd to panic
on 32-bit systems. Within the packetQueue we utilize atomics heavily.
However, it's the caller's job to ensure 64-bit alignment of 64-bit words
accessed atomically. This is documented within the sync/atomic package
as a set of known bugs.

The old alignment of this struct was:

⛰  structlayout github.com/lightningnetwork/lnd/htlcswitch packetQueue
packetQueue.queueLen int32: 0-4 (size 4, align 4)
padding: 4-8 (size 4, align 0)
packetQueue.totalHtlcAmt int64: 8-16 (size 8, align 8)
packetQueue.queueCond *sync.Cond: 16-24 (size 8, align 8)
packetQueue.queueMtx.state int32: 24-28 (size 4, align 4)
packetQueue.queueMtx.sema uint32: 28-32 (size 4, align 4)
packetQueue.queue []*github.com/lightningnetwork/lnd/htlcswitch.htlcPacket: 32-56 (size 24, align 8)
packetQueue.outgoingPkts chan *github.com/lightningnetwork/lnd/htlcswitch.htlcPacket: 56-64 (size 8, align 8)
packetQueue.freeSlots chan struct{}: 64-72 (size 8, align 8)
packetQueue.wg.noCopy sync.noCopy: 72-72 (size 0, align 1)
packetQueue.wg.state1 [12]byte: 72-84 (size 12, align 1)
packetQueue.wg.sema uint32: 84-88 (size 4, align 4)
packetQueue.quit chan struct{}: 88-96 (size 8, align 8)

After this commit, the new alignment of this sturct is:

⛰  structlayout  -json github.com/lightningnetwork/lnd/htlcswitch packetQueue | structlayout-optimize
packetQueue.queue []*github.com/lightningnetwork/lnd/htlcswitch.htlcPacket: 0-24 (size 24, align 8)
packetQueue.wg struct: 24-40 (size 16, align 8)
packetQueue.freeSlots chan struct{}: 40-48 (size 8, align 8)
packetQueue.queueCond *sync.Cond: 48-56 (size 8, align 8)
packetQueue.queueMtx struct: 56-64 (size 8, align 8)
packetQueue.outgoingPkts chan *github.com/lightningnetwork/lnd/htlcswitch.htlcPacket: 64-72 (size 8, align 8)
packetQueue.totalHtlcAmt int64: 72-80 (size 8, align 8)
packetQueue.quit chan struct{}: 80-88 (size 8, align 8)
packetQueue.queueLen int32: 88-92 (size 4, align 8)
padding: 92-96 (size 4, align 0)

Fixes #505, and #463.
This commit is contained in:
Olaoluwa Osuntokun 2017-12-22 16:32:11 +01:00 committed by GitHub
parent 3b986b4c14
commit 151a4325b1
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 23 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

44
htlcswitch/queue.go
View File

@ -17,6 +17,29 @@ import (
// to signal the number of slots available, and a condition variable to allow // to signal the number of slots available, and a condition variable to allow
// the packetQueue to know when new items have been added to the queue. // the packetQueue to know when new items have been added to the queue.
type packetQueue struct { type packetQueue struct {
queue []*htlcPacket
wg sync.WaitGroup
// freeSlots serves as a semaphore who's current value signals the
// number of available slots on the commitment transaction.
freeSlots chan struct{}
queueCond *sync.Cond
queueMtx sync.Mutex
// outgoingPkts is a channel that the channelLink will receive on in
// order to drain the packetQueue as new slots become available on the
// commitment transaction.
outgoingPkts chan *htlcPacket
// totalHtlcAmt is the sum of the value of all pending HTLC's currently
// residing within the overflow queue. This value should only read or
// modified *atomically*.
totalHtlcAmt int64
quit chan struct{}
// queueLen is an internal counter that reflects the size of the queue // queueLen is an internal counter that reflects the size of the queue
// at any given instance. This value is intended to be use atomically // at any given instance. This value is intended to be use atomically
// as this value is used by internal methods to obtain the length of // as this value is used by internal methods to obtain the length of
@ -24,27 +47,6 @@ type packetQueue struct {
// deadlock situation where the main goroutine is attempting a send // deadlock situation where the main goroutine is attempting a send
// with the lock held. // with the lock held.
queueLen int32 queueLen int32
// totalHtlcAmt is the sum of the value of all pending HTLC's currently
// residing within the overflow queue. This value should only read or
// modified *atomically*.
totalHtlcAmt int64
queueCond *sync.Cond
queueMtx sync.Mutex
queue []*htlcPacket
// outgoingPkts is a channel that the channelLink will receive on in
// order to drain the packetQueue as new slots become available on the
// commitment transaction.
outgoingPkts chan *htlcPacket
// freeSlots serves as a semaphore who's current value signals the
// number of available slots on the commitment transaction.
freeSlots chan struct{}
wg sync.WaitGroup
quit chan struct{}
} }
// newPacketQueue returns a new instance of the packetQueue. The maxFreeSlots // newPacketQueue returns a new instance of the packetQueue. The maxFreeSlots