From d04adebaab86ac30aca463b06528fc22430598ac Mon Sep 17 00:00:00 2001 From: Bhasker Hariharan Date: Wed, 25 Mar 2020 10:54:19 -0700 Subject: Fix data-race in endpoint.Readiness PiperOrigin-RevId: 302924789 --- pkg/tcpip/transport/tcp/accept.go | 46 ++++++++++++-------- pkg/tcpip/transport/tcp/endpoint.go | 70 ++++++++++++++++++++----------- pkg/tcpip/transport/tcp/endpoint_state.go | 3 ++ 3 files changed, 77 insertions(+), 42 deletions(-) (limited to 'pkg/tcpip') diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go index b4c4c8ab1..375ca21f6 100644 --- a/pkg/tcpip/transport/tcp/accept.go +++ b/pkg/tcpip/transport/tcp/accept.go @@ -365,21 +365,29 @@ func (l *listenContext) closeAllPendingEndpoints() { } // deliverAccepted delivers the newly-accepted endpoint to the listener. If the -// endpoint has transitioned out of the listen state, the new endpoint is closed -// instead. +// endpoint has transitioned out of the listen state (acceptedChan is nil), +// the new endpoint is closed instead. func (e *endpoint) deliverAccepted(n *endpoint) { e.mu.Lock() - state := e.EndpointState() e.pendingAccepted.Add(1) - defer e.pendingAccepted.Done() - acceptedChan := e.acceptedChan e.mu.Unlock() + defer e.pendingAccepted.Done() - if state == StateListen { - acceptedChan <- n - e.waiterQueue.Notify(waiter.EventIn) - } else { - n.Close() + e.acceptMu.Lock() + for { + if e.acceptedChan == nil { + e.acceptMu.Unlock() + n.Close() + return + } + select { + case e.acceptedChan <- n: + e.acceptMu.Unlock() + e.waiterQueue.Notify(waiter.EventIn) + return + default: + e.acceptCond.Wait() + } } } @@ -420,11 +428,13 @@ func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts *header } func (e *endpoint) incSynRcvdCount() bool { - if e.synRcvdCount >= cap(e.acceptedChan) { - return false + e.acceptMu.Lock() + canInc := e.synRcvdCount < cap(e.acceptedChan) + e.acceptMu.Unlock() + if canInc { + e.synRcvdCount++ } - e.synRcvdCount++ - return true + return canInc } func (e *endpoint) decSynRcvdCount() { @@ -432,10 +442,10 @@ func (e *endpoint) decSynRcvdCount() { } func (e *endpoint) acceptQueueIsFull() bool { - if l, c := len(e.acceptedChan)+e.synRcvdCount, cap(e.acceptedChan); l >= c { - return true - } - return false + e.acceptMu.Lock() + full := len(e.acceptedChan)+e.synRcvdCount >= cap(e.acceptedChan) + e.acceptMu.Unlock() + return full } // handleListenSegment is called when a listening endpoint receives a segment diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go index b6e571361..1ebee0cfe 100644 --- a/pkg/tcpip/transport/tcp/endpoint.go +++ b/pkg/tcpip/transport/tcp/endpoint.go @@ -291,6 +291,7 @@ func (*EndpointInfo) IsEndpointInfo() {} // The following three mutexes can be acquired independent of e.mu but if // acquired with e.mu then e.mu must be acquired first. // +// e.acceptMu -> protects acceptedChan. // e.rcvListMu -> Protects the rcvList and associated fields. // e.sndBufMu -> Protects the sndQueue and associated fields. // e.lastErrorMu -> Protects the lastError field. @@ -533,6 +534,23 @@ type endpoint struct { // to the acceptedChan below terminate before we close acceptedChan. pendingAccepted sync.WaitGroup `state:"nosave"` + // acceptMu protects acceptedChan. + acceptMu sync.Mutex `state:"nosave"` + + // acceptCond is a condition variable that can be used to block on when + // acceptedChan is full and an endpoint is ready to be delivered. + // + // This condition variable is required because just blocking on sending + // to acceptedChan does not work in cases where endpoint.Listen is + // called twice with different backlog values. In such cases the channel + // is closed and a new one created. Any pending goroutines blocking on + // the write to the channel will panic. + // + // We use this condition variable to block/unblock goroutines which + // tried to deliver an endpoint but couldn't because accept backlog was + // full ( See: endpoint.deliverAccepted ). + acceptCond *sync.Cond `state:"nosave"` + // acceptedChan is used by a listening endpoint protocol goroutine to // send newly accepted connections to the endpoint so that they can be // read by Accept() calls. @@ -814,6 +832,7 @@ func newEndpoint(s *stack.Stack, netProto tcpip.NetworkProtocolNumber, waiterQue e.segmentQueue.setLimit(MaxUnprocessedSegments) e.tsOffset = timeStampOffset() + e.acceptCond = sync.NewCond(&e.acceptMu) return e } @@ -834,9 +853,11 @@ func (e *endpoint) Readiness(mask waiter.EventMask) waiter.EventMask { case StateListen: // Check if there's anything in the accepted channel. if (mask & waiter.EventIn) != 0 { + e.acceptMu.Lock() if len(e.acceptedChan) > 0 { result |= waiter.EventIn } + e.acceptMu.Unlock() } } if e.EndpointState().connected() { @@ -981,29 +1002,19 @@ func (e *endpoint) closeNoShutdownLocked() { // closePendingAcceptableConnections closes all connections that have completed // handshake but not yet been delivered to the application. func (e *endpoint) closePendingAcceptableConnectionsLocked() { - done := make(chan struct{}) - // Spin a goroutine up as ranging on e.acceptedChan will just block when - // there are no more connections in the channel. Using a non-blocking - // select does not work as it can potentially select the default case - // even when there are pending writes but that are not yet written to - // the channel. - go func() { - defer close(done) - for n := range e.acceptedChan { - n.notifyProtocolGoroutine(notifyReset) - // close all connections that have completed but - // not accepted by the application. - n.Close() - } - }() - // pendingAccepted(see endpoint.deliverAccepted) tracks the number of - // endpoints which have completed handshake but are not yet written to - // the e.acceptedChan. We wait here till the goroutine above can drain - // all such connections from e.acceptedChan. - e.pendingAccepted.Wait() + e.acceptMu.Lock() + if e.acceptedChan == nil { + e.acceptMu.Unlock() + return + } + close(e.acceptedChan) - <-done e.acceptedChan = nil + e.acceptCond.Broadcast() + e.acceptMu.Unlock() + + // Wait for all pending endpoints to close. + e.pendingAccepted.Wait() } // cleanupLocked frees all resources associated with the endpoint. It is called @@ -1012,9 +1023,7 @@ func (e *endpoint) closePendingAcceptableConnectionsLocked() { func (e *endpoint) cleanupLocked() { // Close all endpoints that might have been accepted by TCP but not by // the client. - if e.acceptedChan != nil { - e.closePendingAcceptableConnectionsLocked() - } + e.closePendingAcceptableConnectionsLocked() e.workerCleanup = false @@ -2204,6 +2213,8 @@ func (e *endpoint) listen(backlog int) *tcpip.Error { if e.EndpointState() == StateListen && !e.workerCleanup { // Adjust the size of the channel iff we can fix existing // pending connections into the new one. + e.acceptMu.Lock() + defer e.acceptMu.Unlock() if len(e.acceptedChan) > backlog { return tcpip.ErrInvalidEndpointState } @@ -2216,6 +2227,11 @@ func (e *endpoint) listen(backlog int) *tcpip.Error { for ep := range origChan { e.acceptedChan <- ep } + + // Notify any blocked goroutines that they can attempt to + // deliver endpoints again. + e.acceptCond.Broadcast() + return nil } @@ -2245,9 +2261,12 @@ func (e *endpoint) listen(backlog int) *tcpip.Error { // The channel may be non-nil when we're restoring the endpoint, and it // may be pre-populated with some previously accepted (but not Accepted) // endpoints. + e.acceptMu.Lock() if e.acceptedChan == nil { e.acceptedChan = make(chan *endpoint, backlog) } + e.acceptMu.Unlock() + e.workerRunning = true go e.protocolListenLoop( // S/R-SAFE: drained on save. seqnum.Size(e.receiveBufferAvailable())) @@ -2276,9 +2295,12 @@ func (e *endpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) { } // Get the new accepted endpoint. + e.acceptMu.Lock() + defer e.acceptMu.Unlock() var n *endpoint select { case n = <-e.acceptedChan: + e.acceptCond.Signal() default: return nil, nil, tcpip.ErrWouldBlock } diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go index 9175de441..c3c692555 100644 --- a/pkg/tcpip/transport/tcp/endpoint_state.go +++ b/pkg/tcpip/transport/tcp/endpoint_state.go @@ -173,6 +173,9 @@ func (e *endpoint) afterLoad() { // Restore the endpoint to InitialState as it will be moved to // its origEndpointState during Resume. e.state = StateInitial + // Condition variables and mutexs are not S/R'ed so reinitialize + // acceptCond with e.acceptMu. + e.acceptCond = sync.NewCond(&e.acceptMu) stack.StackFromEnv.RegisterRestoredEndpoint(e) } -- cgit v1.2.3