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Merge pull request #1859 from fjl/fix-discover-refresh-race 

p2p/discover: fix race involving the seed node iterator
This commit is contained in:
Jeffrey Wilcke 2015-09-30 08:21:40 -07:00
parent 46ad5a5f5b 32dda97602
commit e3ac56d502
6 changed files with 205 additions and 189 deletions
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92
p2p/discover/database.go
View File

@ -21,6 +21,7 @@ package discover
import (
"bytes"
"crypto/rand"
"encoding/binary"
"os"
"sync"
@ -47,10 +48,7 @@ var (
// nodeDB stores all nodes we know about.
type nodeDB struct {
lvl *leveldb.DB // Interface to the database itself
seeder iterator.Iterator // Iterator for fetching possible seed nodes
self NodeID // Own node id to prevent adding it into the database
runner sync.Once // Ensures we can start at most one expirer
quit chan struct{} // Channel to signal the expiring thread to stop
}
@ -302,52 +300,70 @@ func (db *nodeDB) updateFindFails(id NodeID, fails int) error {
return db.storeInt64(makeKey(id, nodeDBDiscoverFindFails), int64(fails))
}
// querySeeds retrieves a batch of nodes to be used as potential seed servers
// during bootstrapping the node into the network.
//
// Ideal seeds are the most recently seen nodes (highest probability to be still
// alive), but yet untried. However, since leveldb only supports dumb iteration
// we will instead start pulling in potential seeds that haven't been yet pinged
// since the start of the boot procedure.
//
// If the database runs out of potential seeds, we restart the startup counter
// and start iterating over the peers again.
func (db *nodeDB) querySeeds(n int) []*Node {
// Create a new seed iterator if none exists
if db.seeder == nil {
db.seeder = db.lvl.NewIterator(nil, nil)
// querySeeds retrieves random nodes to be used as potential seed nodes
// for bootstrapping.
func (db *nodeDB) querySeeds(n int, maxAge time.Duration) []*Node {
var (
now = time.Now()
nodes = make([]*Node, 0, n)
it = db.lvl.NewIterator(nil, nil)
id NodeID
)
defer it.Release()
seek:
for seeks := 0; len(nodes) < n && seeks < n*5; seeks++ {
// Seek to a random entry. The first byte is incremented by a
// random amount each time in order to increase the likelihood
// of hitting all existing nodes in very small databases.
ctr := id[0]
rand.Read(id[:])
id[0] = ctr + id[0]%16
it.Seek(makeKey(id, nodeDBDiscoverRoot))
n := nextNode(it)
if n == nil {
id[0] = 0
continue seek // iterator exhausted
}
// Iterate over the nodes and find suitable seeds
nodes := make([]*Node, 0, n)
for len(nodes) < n && db.seeder.Next() {
// Iterate until a discovery node is found
id, field := splitKey(db.seeder.Key())
if field != nodeDBDiscoverRoot {
continue
if n.ID == db.self {
continue seek
}
// Dump it if its a self reference
if bytes.Compare(id[:], db.self[:]) == 0 {
db.deleteNode(id)
continue
if now.Sub(db.lastPong(n.ID)) > maxAge {
continue seek
}
// Load it as a potential seed
if node := db.node(id); node != nil {
nodes = append(nodes, node)
for i := range nodes {
if nodes[i].ID == n.ID {
continue seek // duplicate
}
}
// Release the iterator if we reached the end
if len(nodes) == 0 {
db.seeder.Release()
db.seeder = nil
nodes = append(nodes, n)
}
return nodes
}
// reads the next node record from the iterator, skipping over other
// database entries.
func nextNode(it iterator.Iterator) *Node {
for end := false; !end; end = !it.Next() {
id, field := splitKey(it.Key())
if field != nodeDBDiscoverRoot {
continue
}
var n Node
if err := rlp.DecodeBytes(it.Value(), &n); err != nil {
if glog.V(logger.Warn) {
glog.Errorf("invalid node %x: %v", id, err)
}
continue
}
return &n
}
return nil
}
// close flushes and closes the database files.
func (db *nodeDB) close() {
if db.seeder != nil {
db.seeder.Release()
}
close(db.quit)
db.lvl.Close()
}

103
p2p/discover/database_test.go
View File

@ -162,9 +162,33 @@ var nodeDBSeedQueryNodes = []struct {
node *Node
pong time.Time
}{
// This one should not be in the result set because its last
// pong time is too far in the past.
{
node: newNode(
MustHexID("0x01d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
MustHexID("0x84d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
net.IP{127, 0, 0, 3},
30303,
30303,
),
pong: time.Now().Add(-3 * time.Hour),
},
// This one shouldn't be in in the result set because its
// nodeID is the local node's ID.
{
node: newNode(
MustHexID("0x57d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
net.IP{127, 0, 0, 3},
30303,
30303,
),
pong: time.Now().Add(-4 * time.Second),
},
// These should be in the result set.
{
node: newNode(
MustHexID("0x22d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
net.IP{127, 0, 0, 1},
30303,
30303,
@ -173,7 +197,7 @@ var nodeDBSeedQueryNodes = []struct {
},
{
node: newNode(
MustHexID("0x02d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
MustHexID("0x44d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
net.IP{127, 0, 0, 2},
30303,
30303,
@ -182,7 +206,7 @@ var nodeDBSeedQueryNodes = []struct {
},
{
node: newNode(
MustHexID("0x03d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
MustHexID("0xe2d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
net.IP{127, 0, 0, 3},
30303,
30303,
@ -192,7 +216,7 @@ var nodeDBSeedQueryNodes = []struct {
}
func TestNodeDBSeedQuery(t *testing.T) {
db, _ := newNodeDB("", Version, NodeID{})
db, _ := newNodeDB("", Version, nodeDBSeedQueryNodes[1].node.ID)
defer db.close()
// Insert a batch of nodes for querying
@ -200,20 +224,24 @@ func TestNodeDBSeedQuery(t *testing.T) {
if err := db.updateNode(seed.node); err != nil {
t.Fatalf("node %d: failed to insert: %v", i, err)
}
if err := db.updateLastPong(seed.node.ID, seed.pong); err != nil {
t.Fatalf("node %d: failed to insert lastPong: %v", i, err)
}
}
// Retrieve the entire batch and check for duplicates
seeds := db.querySeeds(2 * len(nodeDBSeedQueryNodes))
if len(seeds) != len(nodeDBSeedQueryNodes) {
t.Errorf("seed count mismatch: have %v, want %v", len(seeds), len(nodeDBSeedQueryNodes))
}
seeds := db.querySeeds(len(nodeDBSeedQueryNodes)*2, time.Hour)
have := make(map[NodeID]struct{})
for _, seed := range seeds {
have[seed.ID] = struct{}{}
}
want := make(map[NodeID]struct{})
for _, seed := range nodeDBSeedQueryNodes {
for _, seed := range nodeDBSeedQueryNodes[2:] {
want[seed.node.ID] = struct{}{}
}
if len(seeds) != len(want) {
t.Errorf("seed count mismatch: have %v, want %v", len(seeds), len(want))
}
for id, _ := range have {
if _, ok := want[id]; !ok {
t.Errorf("extra seed: %v", id)
@ -224,63 +252,6 @@ func TestNodeDBSeedQuery(t *testing.T) {
t.Errorf("missing seed: %v", id)
}
}
// Make sure the next batch is empty (seed EOF)
seeds = db.querySeeds(2 * len(nodeDBSeedQueryNodes))
if len(seeds) != 0 {
t.Errorf("seed count mismatch: have %v, want %v", len(seeds), 0)
}
}
func TestNodeDBSeedQueryContinuation(t *testing.T) {
db, _ := newNodeDB("", Version, NodeID{})
defer db.close()
// Insert a batch of nodes for querying
for i, seed := range nodeDBSeedQueryNodes {
if err := db.updateNode(seed.node); err != nil {
t.Fatalf("node %d: failed to insert: %v", i, err)
}
}
// Iteratively retrieve the batch, checking for an empty batch on reset
for i := 0; i < len(nodeDBSeedQueryNodes); i++ {
if seeds := db.querySeeds(1); len(seeds) != 1 {
t.Errorf("1st iteration %d: seed count mismatch: have %v, want %v", i, len(seeds), 1)
}
}
if seeds := db.querySeeds(1); len(seeds) != 0 {
t.Errorf("reset: seed count mismatch: have %v, want %v", len(seeds), 0)
}
for i := 0; i < len(nodeDBSeedQueryNodes); i++ {
if seeds := db.querySeeds(1); len(seeds) != 1 {
t.Errorf("2nd iteration %d: seed count mismatch: have %v, want %v", i, len(seeds), 1)
}
}
}
func TestNodeDBSelfSeedQuery(t *testing.T) {
// Assign a node as self to verify evacuation
self := nodeDBSeedQueryNodes[0].node.ID
db, _ := newNodeDB("", Version, self)
defer db.close()
// Insert a batch of nodes for querying
for i, seed := range nodeDBSeedQueryNodes {
if err := db.updateNode(seed.node); err != nil {
t.Fatalf("node %d: failed to insert: %v", i, err)
}
}
// Retrieve the entire batch and check that self was evacuated
seeds := db.querySeeds(2 * len(nodeDBSeedQueryNodes))
if len(seeds) != len(nodeDBSeedQueryNodes)-1 {
t.Errorf("seed count mismatch: have %v, want %v", len(seeds), len(nodeDBSeedQueryNodes)-1)
}
have := make(map[NodeID]struct{})
for _, seed := range seeds {
have[seed.ID] = struct{}{}
}
if _, ok := have[self]; ok {
t.Errorf("self not evacuated")
}
}
func TestNodeDBPersistency(t *testing.T) {

144
p2p/discover/table.go
View File

@ -44,6 +44,10 @@ const (
maxBondingPingPongs = 16
maxFindnodeFailures = 5
autoRefreshInterval = 1 * time.Hour
seedCount = 30
seedMaxAge = 5 * 24 * time.Hour
)
type Table struct {
@ -52,6 +56,10 @@ type Table struct {
nursery []*Node // bootstrap nodes
db *nodeDB // database of known nodes
refreshReq chan struct{}
closeReq chan struct{}
closed chan struct{}
bondmu sync.Mutex
bonding map[NodeID]*bondproc
bondslots chan struct{} // limits total number of active bonding processes
@ -80,10 +88,7 @@ type transport interface {
// bucket contains nodes, ordered by their last activity. the entry
// that was most recently active is the first element in entries.
type bucket struct {
lastLookup time.Time
entries []*Node
}
type bucket struct{ entries []*Node }
func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string) *Table {
// If no node database was given, use an in-memory one
@ -98,6 +103,9 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
self: newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
bonding: make(map[NodeID]*bondproc),
bondslots: make(chan struct{}, maxBondingPingPongs),
refreshReq: make(chan struct{}),
closeReq: make(chan struct{}),
closed: make(chan struct{}),
}
for i := 0; i < cap(tab.bondslots); i++ {
tab.bondslots <- struct{}{}
@ -105,6 +113,7 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
for i := range tab.buckets {
tab.buckets[i] = new(bucket)
}
go tab.refreshLoop()
return tab
}
@ -163,10 +172,12 @@ func randUint(max uint32) uint32 {
// Close terminates the network listener and flushes the node database.
func (tab *Table) Close() {
if tab.net != nil {
tab.net.close()
select {
case <-tab.closed:
// already closed.
case tab.closeReq <- struct{}{}:
<-tab.closed // wait for refreshLoop to end.
}
tab.db.close()
}
// Bootstrap sets the bootstrap nodes. These nodes are used to connect
@ -183,7 +194,7 @@ func (tab *Table) Bootstrap(nodes []*Node) {
tab.nursery = append(tab.nursery, &cpy)
}
tab.mutex.Unlock()
tab.refresh()
tab.requestRefresh()
}
// Lookup performs a network search for nodes close
@ -204,15 +215,13 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
asked[tab.self.ID] = true
tab.mutex.Lock()
// update last lookup stamp (for refresh logic)
tab.buckets[logdist(tab.self.sha, target)].lastLookup = time.Now()
// generate initial result set
result := tab.closest(target, bucketSize)
tab.mutex.Unlock()
// If the result set is empty, all nodes were dropped, refresh
// If the result set is empty, all nodes were dropped, refresh.
if len(result.entries) == 0 {
tab.refresh()
tab.requestRefresh()
return nil
}
@ -257,57 +266,87 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
return result.entries
}
// refresh performs a lookup for a random target to keep buckets full, or seeds
// the table if it is empty (initial bootstrap or discarded faulty peers).
func (tab *Table) refresh() {
seed := true
// If the discovery table is empty, seed with previously known nodes
tab.mutex.Lock()
for _, bucket := range tab.buckets {
if len(bucket.entries) > 0 {
seed = false
break
func (tab *Table) requestRefresh() {
select {
case tab.refreshReq <- struct{}{}:
case <-tab.closed:
}
}
tab.mutex.Unlock()
// If the table is not empty, try to refresh using the live entries
if !seed {
func (tab *Table) refreshLoop() {
defer func() {
tab.db.close()
if tab.net != nil {
tab.net.close()
}
close(tab.closed)
}()
timer := time.NewTicker(autoRefreshInterval)
var done chan struct{}
for {
select {
case <-timer.C:
if done == nil {
done = make(chan struct{})
go tab.doRefresh(done)
}
case <-tab.refreshReq:
if done == nil {
done = make(chan struct{})
go tab.doRefresh(done)
}
case <-done:
done = nil
case <-tab.closeReq:
if done != nil {
<-done
}
return
}
}
}
// doRefresh performs a lookup for a random target to keep buckets
// full. seed nodes are inserted if the table is empty (initial
// bootstrap or discarded faulty peers).
func (tab *Table) doRefresh(done chan struct{}) {
defer close(done)
// The Kademlia paper specifies that the bucket refresh should
// perform a refresh in the least recently used bucket. We cannot
// perform a lookup in the least recently used bucket. We cannot
// adhere to this because the findnode target is a 512bit value
// (not hash-sized) and it is not easily possible to generate a
// sha3 preimage that falls into a chosen bucket.
//
// We perform a lookup with a random target instead.
var target NodeID
rand.Read(target[:])
result := tab.Lookup(target)
if len(result) == 0 {
// Lookup failed, seed after all
seed = true
}
if len(result) > 0 {
return
}
if seed {
// Pick a batch of previously know seeds to lookup with
seeds := tab.db.querySeeds(10)
for _, seed := range seeds {
glog.V(logger.Debug).Infoln("Seeding network with", seed)
// The table is empty. Load nodes from the database and insert
// them. This should yield a few previously seen nodes that are
// (hopefully) still alive.
seeds := tab.db.querySeeds(seedCount, seedMaxAge)
seeds = tab.bondall(append(seeds, tab.nursery...))
if glog.V(logger.Debug) {
if len(seeds) == 0 {
glog.Infof("no seed nodes found")
}
nodes := append(tab.nursery, seeds...)
for _, n := range seeds {
age := time.Since(tab.db.lastPong(n.ID))
glog.Infof("seed node (age %v): %v", age, n)
}
}
tab.mutex.Lock()
tab.stuff(seeds)
tab.mutex.Unlock()
// Bond with all the seed nodes (will pingpong only if failed recently)
bonded := tab.bondall(nodes)
if len(bonded) > 0 {
// Finally, do a self lookup to fill up the buckets.
tab.Lookup(tab.self.ID)
}
// TODO: the Kademlia paper says that we're supposed to perform
// random lookups in all buckets further away than our closest neighbor.
}
}
// closest returns the n nodes in the table that are closest to the
// given id. The caller must hold tab.mutex.
@ -373,8 +412,9 @@ func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16
}
// If the node is unknown (non-bonded) or failed (remotely unknown), bond from scratch
var result error
if node == nil || fails > 0 {
glog.V(logger.Detail).Infof("Bonding %x: known=%v, fails=%v", id[:8], node != nil, fails)
age := time.Since(tab.db.lastPong(id))
if node == nil || fails > 0 || age > nodeDBNodeExpiration {
glog.V(logger.Detail).Infof("Bonding %x: known=%t, fails=%d age=%v", id[:8], node != nil, fails, age)
tab.bondmu.Lock()
w := tab.bonding[id]
@ -435,13 +475,17 @@ func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAdd
// ping a remote endpoint and wait for a reply, also updating the node
// database accordingly.
func (tab *Table) ping(id NodeID, addr *net.UDPAddr) error {
// Update the last ping and send the message
tab.db.updateLastPing(id, time.Now())
if err := tab.net.ping(id, addr); err != nil {
return err
}
// Pong received, update the database and return
tab.db.updateLastPong(id, time.Now())
// Start the background expiration goroutine after the first
// successful communication. Subsequent calls have no effect if it
// is already running. We do this here instead of somewhere else
// so that the search for seed nodes also considers older nodes
// that would otherwise be removed by the expiration.
tab.db.ensureExpirer()
return nil
}

3
p2p/discover/table_test.go
View File

@ -514,9 +514,6 @@ func (tn *preminedTestnet) findnode(toid NodeID, toaddr *net.UDPAddr, target Nod
if toaddr.Port == 0 {
panic("query to node at distance 0")
}
if target != tn.target {
panic("findnode with wrong target")
}
next := uint16(toaddr.Port) - 1
var result []*Node
for i, id := range tn.dists[toaddr.Port] {

11
p2p/discover/udp.go
View File

@ -39,7 +39,6 @@ var (
errPacketTooSmall = errors.New("too small")
errBadHash = errors.New("bad hash")
errExpired = errors.New("expired")
errBadVersion = errors.New("version mismatch")
errUnsolicitedReply = errors.New("unsolicited reply")
errUnknownNode = errors.New("unknown node")
errTimeout = errors.New("RPC timeout")
@ -52,8 +51,6 @@ const (
respTimeout = 500 * time.Millisecond
sendTimeout = 500 * time.Millisecond
expiration = 20 * time.Second
refreshInterval = 1 * time.Hour
)
// RPC packet types
@ -312,10 +309,8 @@ func (t *udp) loop() {
plist = list.New()
timeout = time.NewTimer(0)
nextTimeout *pending // head of plist when timeout was last reset
refresh = time.NewTicker(refreshInterval)
)
<-timeout.C // ignore first timeout
defer refresh.Stop()
defer timeout.Stop()
resetTimeout := func() {
@ -344,9 +339,6 @@ func (t *udp) loop() {
resetTimeout()
select {
case <-refresh.C:
go t.refresh()
case <-t.closing:
for el := plist.Front(); el != nil; el = el.Next() {
el.Value.(*pending).errc <- errClosed
@ -529,9 +521,6 @@ func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) er
if expired(req.Expiration) {
return errExpired
}
if req.Version != Version {
return errBadVersion
}
t.send(from, pongPacket, pong{
To: makeEndpoint(from, req.From.TCP),
ReplyTok: mac,

1
p2p/discover/udp_test.go
View File

@ -122,7 +122,6 @@ func TestUDP_packetErrors(t *testing.T) {
defer test.table.Close()
test.packetIn(errExpired, pingPacket, &ping{From: testRemote, To: testLocalAnnounced, Version: Version})
test.packetIn(errBadVersion, pingPacket, &ping{From: testRemote, To: testLocalAnnounced, Version: 99, Expiration: futureExp})
test.packetIn(errUnsolicitedReply, pongPacket, &pong{ReplyTok: []byte{}, Expiration: futureExp})
test.packetIn(errUnknownNode, findnodePacket, &findnode{Expiration: futureExp})
test.packetIn(errUnsolicitedReply, neighborsPacket, &neighbors{Expiration: futureExp})