From 5d909dd49c0b67f7f4d07fe832dc9aebbde731fb Mon Sep 17 00:00:00 2001 From: Bhasker Hariharan Date: Fri, 23 Oct 2020 09:41:05 -0700 Subject: Decrement e.synRcvdCount once handshake is complete. Earlier the count was dropped only after calling e.deliverAccepted. This lead to an issue where there were no connections in SYN-RCVD state for the listening endpoint but e.synRcvdCount would not be zero because it was being reduced only when handleSynSegment returned after deliverAccepted returned. This issue is seen when the Nth SYN for a listen backlog of size N which would cause the listen backlog to be full gets dropped occasionally. This happens when the new SYN comes at when the previous completed endpoint has been delivered to the accept queue but the synRcvdCount hasn't yet been decremented because the goroutine running handleSynSegment has not yet completed. PiperOrigin-RevId: 338690646 --- pkg/tcpip/transport/tcp/accept.go | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) (limited to 'pkg/tcpip/transport/tcp/accept.go') diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go index b706438bd..6b3238d6b 100644 --- a/pkg/tcpip/transport/tcp/accept.go +++ b/pkg/tcpip/transport/tcp/accept.go @@ -425,20 +425,17 @@ func (e *endpoint) notifyAborted() { // cookies to accept connections. func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts *header.TCPSynOptions) { defer ctx.synRcvdCount.dec() - defer func() { - e.mu.Lock() - e.decSynRcvdCount() - e.mu.Unlock() - }() defer s.decRef() n, err := ctx.createEndpointAndPerformHandshake(s, opts, &waiter.Queue{}, e.owner) if err != nil { e.stack.Stats().TCP.FailedConnectionAttempts.Increment() e.stats.FailedConnectionAttempts.Increment() + e.decSynRcvdCount() return } ctx.removePendingEndpoint(n) + e.decSynRcvdCount() n.startAcceptedLoop() e.stack.Stats().TCP.PassiveConnectionOpenings.Increment() @@ -456,7 +453,9 @@ func (e *endpoint) incSynRcvdCount() bool { } func (e *endpoint) decSynRcvdCount() { + e.mu.Lock() e.synRcvdCount-- + e.mu.Unlock() } func (e *endpoint) acceptQueueIsFull() bool { -- cgit v1.2.3