From: Russ Cox <rsc@golang.org>
Date: Mon, 8 Sep 2014 03:16:12 +0000 (-0400)
Subject: runtime: fix semacquire->acquireSudog->malloc->gogc->semacquire loop
X-Git-Tag: go1.4beta1~494
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=71de7e7539a9d139daee6f4467ce73995b37b5a0;p=gostls13.git

runtime: fix semacquire->acquireSudog->malloc->gogc->semacquire loop

This is what broke the build at
http://build.golang.org/log/d9c6d334be16cbab85e99fddc6b4ba034319bd4e

LGTM=iant
R=golang-codereviews, iant
CC=dvyukov, golang-codereviews, khr, r
https://golang.org/cl/135580043
---

diff --git a/src/pkg/runtime/proc.go b/src/pkg/runtime/proc.go
index a9cac266ba..48b8cbe394 100644
--- a/src/pkg/runtime/proc.go
+++ b/src/pkg/runtime/proc.go
@@ -75,7 +75,19 @@ func acquireSudog() *sudog {
 		c.sudogcache = s.next
 		return s
 	}
-	return new(sudog)
+
+	// Delicate dance: the semaphore implementation calls
+	// acquireSudog, acquireSudog calls new(sudog),
+	// new calls malloc, malloc can call the garbage collector,
+	// and the garbage collector calls the semaphore implementation
+	// in stoptheworld.
+	// Break the cycle by doing acquirem/releasem around new(sudog).
+	// The acquirem/releasem increments m.locks during new(sudog),
+	// which keeps the garbage collector from being invoked.
+	mp := acquirem()
+	p := new(sudog)
+	releasem(mp)
+	return p
 }
 
 //go:nosplit