From: cuiweixie <cuiweixie@gmail.com>
Date: Thu, 25 Aug 2022 03:10:52 +0000 (+0800)
Subject: runtime: convert mcache.flushGen to atomic type
X-Git-Tag: go1.20rc1~1329
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=a25a34abe986bd78ab9a543d2a96cbce427a4f3c;p=gostls13.git

runtime: convert mcache.flushGen to atomic type

For #53821

Change-Id: I90ab52a45b7fb6b9e3ff1d6ea97251549306c7aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/425435
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: xie cui <523516579@qq.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
---

diff --git a/src/runtime/mcache.go b/src/runtime/mcache.go
index e01a99bd6e..ba45034943 100644
--- a/src/runtime/mcache.go
+++ b/src/runtime/mcache.go
@@ -50,7 +50,7 @@ type mcache struct {
 	// was last flushed. If flushGen != mheap_.sweepgen, the spans
 	// in this mcache are stale and need to the flushed so they
 	// can be swept. This is done in acquirep.
-	flushGen uint32
+	flushGen atomic.Uint32
 }
 
 // A gclink is a node in a linked list of blocks, like mlink,
@@ -87,7 +87,7 @@ func allocmcache() *mcache {
 	systemstack(func() {
 		lock(&mheap_.lock)
 		c = (*mcache)(mheap_.cachealloc.alloc())
-		c.flushGen = mheap_.sweepgen
+		c.flushGen.Store(mheap_.sweepgen)
 		unlock(&mheap_.lock)
 	})
 	for i := range c.alloc {
@@ -318,13 +318,14 @@ func (c *mcache) prepareForSweep() {
 	// allocate-black. However, with this approach it's difficult
 	// to avoid spilling mark bits into the *next* GC cycle.
 	sg := mheap_.sweepgen
-	if c.flushGen == sg {
+	flushGen := c.flushGen.Load()
+	if flushGen == sg {
 		return
-	} else if c.flushGen != sg-2 {
-		println("bad flushGen", c.flushGen, "in prepareForSweep; sweepgen", sg)
+	} else if flushGen != sg-2 {
+		println("bad flushGen", flushGen, "in prepareForSweep; sweepgen", sg)
 		throw("bad flushGen")
 	}
 	c.releaseAll()
 	stackcache_clear(c)
-	atomic.Store(&c.flushGen, mheap_.sweepgen) // Synchronizes with gcStart
+	c.flushGen.Store(mheap_.sweepgen) // Synchronizes with gcStart
 }
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 8021a56b9a..3243a15b4d 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -636,7 +636,7 @@ func gcStart(trigger gcTrigger) {
 
 	// Check that all Ps have finished deferred mcache flushes.
 	for _, p := range allp {
-		if fg := atomic.Load(&p.mcache.flushGen); fg != mheap_.sweepgen {
+		if fg := p.mcache.flushGen.Load(); fg != mheap_.sweepgen {
 			println("runtime: p", p.id, "flushGen", fg, "!= sweepgen", mheap_.sweepgen)
 			throw("p mcache not flushed")
 		}