From: Keith Randall <khr@golang.org>
Date: Thu, 24 Jul 2014 21:37:34 +0000 (-0700)
Subject: runtime: set sweepgen atomically before updating span state
X-Git-Tag: go1.4beta1~1019
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=3590d9ce695baa7535537e3d1404de52bf94fae5;p=gostls13.git

runtime: set sweepgen atomically before updating span state

Sweepone may be running while a new span is allocating.  It
must not see the state updated while the sweepgen is unset.

Fixes #8399

LGTM=dvyukov
R=golang-codereviews, dvyukov
CC=golang-codereviews
https://golang.org/cl/118050043
---

diff --git a/src/pkg/runtime/mheap.c b/src/pkg/runtime/mheap.c
index 7ae5a399b3..3a5981d3c7 100644
--- a/src/pkg/runtime/mheap.c
+++ b/src/pkg/runtime/mheap.c
@@ -189,13 +189,13 @@ mheap_alloc(MHeap *h, uintptr npage, int32 sizeclass, bool large)
 	if(s != nil) {
 		// Record span info, because gc needs to be
 		// able to map interior pointer to containing span.
+		runtime·atomicstore(&s->sweepgen, h->sweepgen);
 		s->state = MSpanInUse;
 		s->freelist = nil;
 		s->ref = 0;
 		s->sizeclass = sizeclass;
 		s->elemsize = (sizeclass==0 ? s->npages<<PageShift : runtime·class_to_size[sizeclass]);
 		s->types.compression = MTypes_Empty;
-		s->sweepgen = h->sweepgen;
 
 		// update stats, sweep lists
 		if(large) {