From: Dmitriy Vyukov <dvyukov@google.com>
Date: Tue, 12 Jul 2011 05:21:06 +0000 (-0400)
Subject: runtime: fix data race on runtime·maxstring
X-Git-Tag: weekly.2011-07-19~118
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=f9f21aa1fb45aaa4eece55f192783bfa46df4909;p=gostls13.git

runtime: fix data race on runtime·maxstring
The data race can lead to erroneous output of
"[invalid string]" instead of a string.

R=golang-dev
CC=golang-dev
https://golang.org/cl/4678049
---

diff --git a/src/pkg/runtime/print.c b/src/pkg/runtime/print.c
index b8069aa393..3ce7794957 100644
--- a/src/pkg/runtime/print.c
+++ b/src/pkg/runtime/print.c
@@ -320,7 +320,7 @@ runtime·printpointer(void *p)
 void
 runtime·printstring(String v)
 {
-	extern int32 runtime·maxstring;
+	extern uint32 runtime·maxstring;
 
 	if(v.len > runtime·maxstring) {
 		runtime·write(2, "[invalid string]", 16);
diff --git a/src/pkg/runtime/string.goc b/src/pkg/runtime/string.goc
index b72aa937c3..15b3459ada 100644
--- a/src/pkg/runtime/string.goc
+++ b/src/pkg/runtime/string.goc
@@ -32,19 +32,23 @@ runtime·findnullw(uint16 *s)
 	return l;
 }
 
-int32 runtime·maxstring = 256;
+uint32 runtime·maxstring = 256;
 
 String
 runtime·gostringsize(int32 l)
 {
 	String s;
+	uint32 ms;
 
 	if(l == 0)
 		return runtime·emptystring;
 	s.str = runtime·mal(l+1);	// leave room for NUL for C runtime (e.g., callers of getenv)
 	s.len = l;
-	if(l > runtime·maxstring)
-		runtime·maxstring = l;
+	for(;;) {
+		ms = runtime·maxstring;
+		if((uint32)l <= ms || runtime·cas(&runtime·maxstring, ms, (uint32)l))
+			break;
+	}
 	return s;
 }