From 0b5d55984fc939fdc35128342aa7cb34b0798de6 Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Sat, 6 Apr 2013 22:27:54 -0700
Subject: [PATCH] runtime: fix deadlock in network poller The invariant is that
 there must be at least one running P or a thread polling network. It was
 broken. Fixes #5216.

R=golang-dev, bradfitz, r
CC=golang-dev
https://golang.org/cl/8459043
---
 src/pkg/runtime/proc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 0a131871f3..018a453d62 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -875,6 +875,13 @@ handoffp(P *p)
 		startm(p, false);
 		return;
 	}
+	// If this is the last running P and nobody is polling network,
+	// need to wakeup another M to poll network.
+	if(runtime·sched.npidle == runtime·gomaxprocs-1 && runtime·atomicload64(&runtime·sched.lastpoll) != 0) {
+		runtime·unlock(&runtime·sched);
+		startm(p, false);
+		return;
+	}
 	pidleput(p);
 	runtime·unlock(&runtime·sched);
 }